A year ago I have asked QGIS’s community what were their favourite QGIS new features from 2015 and published this blog post. This year I decided to ask it again. In 2016, we add the release of the second long-term release (2.14 LTR), and two other stable versions (2.16 and 2.18).
2016 was again very productive year for the QGIS community, with lots of improvements and new features landing on QGIS source code, not to speak of all the work already in place for QGIS 3. This is a great assurance of the project’s vitality.
As a balance, I have asked users to choose wich were their favorite new features during 2016 (from the visual changelogs list). As a result, I got the following Top 5 features list.
5 – Paste a style to multiple selected layers or to all layers in a legend group (2.14)
This is a productivity functionaly that I just realized that existed now, with so many people voting on it. If copy/paste styles was, in my opinion, a killer feature, being able to use it in multiple layers or even a group is just great.
4 – fTools plugin has been replaced with Processing algorithms (2.16)
While checking the Vector Menu, the tools seem the same as previous version, but it’s when you open them that you understand the difference. All vector tools, provided until now by the fTools core plugin, were replaced by equivalent processing Algoritms. For the users it means easier access to more functionality, like running the tools in batch mode, or getting outputs as temporary layers. Besides some of the tools have been improved.
3 – Virtual layers (2.14)
This is definitly one of my favourite new features, and it seems I’m not alone. With virtual layers you can run SQL queries using the layers loaded in the project, even when the layers are not stored in a relational database. We are not talking about WHERE statments to filter data, with this you can do real SQL queries, with spatial analysis, aggregations, and so on. Besides, virtual layers will act as VIEWs and any changes to any of the input layers will automatically update the layer.
2 – Speed and memory improvements (2.14)
It’s no surprise that speed and memory improvements we one of the most voted features. Lots of improvements were made for loading and managing large datasets, and this have a tremendous impact in all users. According to the changelog, zoom is faster, selecting features is faster, updating attributes on selected features is faster, and it consumes less memory. So don’t be afraid to put QGIS to the test.
1 – Trace digitising tool (2.14)
If you do lots of digitising, you better look into this new feaure that landed on QGIS 2.14. It allows you to digitize new feature by using other layers boundaries. Besides the quality improvement of layers topology, this can make digitizing almost feel pleasing and fast! Just click the first point, move your mouse around other features edged to pick up more vertex.
There were other new features that also made the delight of many users. For example, several improvements on the labeling, Georeference outputs (eg PDF) from composer (2.16), Filter legend by expression (2.14), 2.5D Renderer. Personally, the Style docker made my day/year. But you can check the full results of the survey, if you like.
Obviously, this list means nothing at all. All new features were of tremendous value, and will be useful for thousands (yes thousands) of people. It was a mere exercise as, with such a diverse QGIS crowd, it would be impossible to build a list that would fit us all. Besides, there were many great enhancements, introduced during 2016, that might have fallen under the radar for most users. Check the visual changelogs for a full list of new features.
On my behalf, to all developers, sponsors, and general QGIS contributors, once again
From time to time, I read articles comparing ArcGIS vs QGIS. Since many of those articles are created from an ArcGIS user point of view, they invariably lead to biased observations on QGIS lack of features. It’s time for a QGIS user perspective, so bare with me on this (a bit) long, totally and openly biased post.
“Hello, my name is Alexandre, and I have been using… QGIS“
This is something I would say at an anonymous QGIS user therapy group. I’m willing to attend one of those because being recently and temporally forced to use ArcGIS Desktop again (don’t ask!), I really really really miss QGIS in many ways.
There was a time when I have used ArcGIS on the regular basis. I used it until version 9.3.1 and then decided to move away (toward the light) into QGIS (1.7.4 I think). At that time, I missed some (or even many?) ArcGIS features, but I was willing to accept it in exchange for the freedom of the Open Source philosophy. Since then, a lot have happened in the QGIS world, and I have been watching it closely. I would expect the same have happened in ArcGIS side, but, as far I can see, it didn’t.
I’m using top shelf ArcGIS Desktop Advanced and I’m struggling to do very basic tasks that simply are nonexistent in ArcGIS. So here’s my short list of QGIS functionalities that I’m longing for. For those of you that use ArcGIS exclusively, some of this features may catch you by surprise.
Warning: For those of you that use ArcGIS exclusively, some of this features may catch you by surprise.
Transparency control
“ArcGIS have transparency! It’s in the Display tab, in the layer’s properties dialog!”
Yes, but… you can only set transparency at the layer level. That is, either it’s all transparent, or it’s not…
In QGIS on the other end, you can set transparency at layer level, feature/symbol level, and color level. You can say that this is being overrated, but check the differences in the following images.
Notice that in QGIS you can set transparency at color level everywhere (or almost everywhere) there is a color to select. This includes annotations (like the ones in the image above), labels and composers items. You can even set transparency in colors by using the RGBA function in an expression! How sweet can that be?
Blending modes
This is one of QGIS’s pristine jewels. The ability to combine layers the way you would do in almost any design/photo editing software. At layer or at feature level, you can control how they will “interact” with other layers or features below. Besides the normal mode, QGIS offers 12 other blending modes: Lighten, Screen, Dodge, Darken, Multiply, Burn, Overlay, Soft light, Hard light, Difference, and Subtract. Check this page to know more about the math behind each one and this image for some examples
It’s not easy to grasp how can this be of any use for cartography before you try it yourself. I had the chance to play around while trying to answer this question.
A very common application for this functionality is when you want to add shadows to simulate the relief by putting a hill shade on top of other layers. In ArcGIS, you can only control the layer transparency, and the result is always a bit pale. But in QGIS, you can keep the strength of the original colors by using the multiply mode in the hill shade layer.
Hypsometry original colorsHypsometry colors paled by transparent hill shadeHypsometry original colors with the hill shade using QGIS multiply blending
You can also use blending modes in the print composer items, allowing you to combine them with other items and textures. This gives you the opportunity to make more “artistic” things without the need to go post-processing in a design software.
Colour Picker Menu
Controlling color is a very important deal for a cartographer and QGIS allow you to control it like the professional you are. You can select your colours using many different interfaces. Interfaces that you might recognize from software like Inkscape, Photoshop, Gimp and others alike.
My favorite one is the color picker. Using color picker, you can pick colors from anywhere on your screen, either from QGIS itself or outside. This is quite handy and productive when you are trying to use a color from your map, it’s legend, a COLOURlovers palette or a company logo.
Picking a color from outside QGIS
You can also copy/paste colors between dialogs, save and import color palettes, and you can even name a color and use it in a variable. With all this available for free, it’s hard to swallow Windows color selector :(.
Vector symbols renderers “powertools”
In ArcGIS, you have a few fancy ways to symbol your vector layers. You got: Single symbol, Unique values, Unique values many fields… and so on. At the first glance, you may think that QGIS lacks some of them. Believe me, it doesn’t! In fact, QGIS offers much more flexibility when you need to symbol your layers.
For starters, it allows you to use fields or expressions on any of the symbols renderers, while ArcGIS only allows the use of fields. Powered by hundreds of functions and the ability to create your owns in python, what you can do with the expression builder has no limits. This means, for instance, that you can combine, select, recalculate, normalize an infinite number of fields to create your own “values” (not to mention that you can tweak your values labels, making it ideal to create the legend).
QGIS Graduated renderer using an expression to calculate population density
And then, in QGIS, you have the special (and kinda very specific) renderers, that make you say “wooooh”. Like the Inverted polygons that allow you to fill the the outside of polygons (nice to mask other features), the Point displacement to show points that are too close to each others, and the Heatmap that will transform, ON-THE-FLY, all your points in a layer into a nice heatmap without the need to convert them to raster (and that will update as soon as you, or anyone else, edits the point features).
Inverted Polygon Renderer masking the outside of an interest area
But I have left the best to the end. The “One rendered to Rule them all”, the Rule-based symbols. With the rule-based renderer, you can add several rules, group them in a tree structure, and set each one with a desired symbol. This gives QGIS users full control of their layer’s symbols, and, paired with expression builder and data-defined properties, opens the door to many wonderful applications.
Rule-based renderer
Atlas
One of my favorite (and missed) features in QGIS is the Map Composer’s Atlas. I know that ArcGIS has its own “Atlas”, the Data Driven Pages, but frankly, it’s simply not the same.
I believe you know the basic functionally that both software allow. You create a map layout and choose a vector layer as coverage, and it will create an output panned or zoomed for each of the layer’s feature. You can also add some labels that will change according to the layers attributes.
But in QGIS, things go a little bit further…
Basically, you can use coverage layer’s attributes and geometry anywhere you can use an expression. And, in QGIS, expressions are everywhere. That way, most layers and map composer items properties can be controlled by a single coverage layer.
Auto-resized maps that fits the coverage features at specific scale using atlas
So, if you pair Atlas it with QGIS data-defined properties, rule-based symbols and expressions, ArcGIS Data Driven Pages are no match. You don’t think so? Try to answer this question then.
Tip: If you really want to leverage your map production, using Spatialite or Postgis databases you can create the perfect atlas coverage layers from views that fit your needs. No data redundancy and they are always updated.
Label and Style dialogs
This one is more of a User Experience thing than an actual feature, but you won’t imagine how refreshing it is to have all Style and Labels options in two single dialogs (with several tabs, of course).
Using the symbol menu in ArcGIS makes me feel like if I’m in the Inception movie, at some point in time, I no longer know where the hell am I. For example, to apply a dashed outline in a fill symbol I needed to open 5 different dialogs, and then go back clicking OK, OK, OK, OK …
ArcGIS “Inception” symbol settings
In QGIS, once in the properties menu, every setting is (almost) one click way. And you just need to press OK (or Apply ) once to see the result!
QGIS Style setting
As an extra, you can copy/paste styles from one layer to another, making styling several layers even faster. And now you say:
“Don’t be silly! In ArcGIS you can import symbols from other layers too.”
Symbols? yes. Labels? No! And if you had lots of work setting your fancy labels, having to do the exact same/similar thing in another layer, it will make you wanna cry… I did.
(I think I will leave the multiple styles per layer vs data frames comparison for another time)
In a GIS world that, more and more, is evolving towards Open Data, Open Standards and OGC Web Services, this reveals a very mercantile approach by ESRI. If I were an ESRI customer, I would feel outraged. <sarcasm>Or maybe not… maybe I would thank the opportunity to yet invest some more money in it’s really advanced features…<\sarcasm>
In QGIS, like everything else, WFS is absolutely free (as in freedom, not free beer). All you need to do is add the WFS server’s URL, and you can add all the layers you want, with the absolute sure that they are as updated as you can get.
Fortunately for ArcGIS users with a low budget, they can easily make a request for a layer using the internet browser :-P.
Or they can simply use QGIS to download it. But, in both cases, be aware that the layers won’t update themselves by magic.
Expression builder
I have already mentioned the use of expressions several times, but for those of you that do not know the expression Builder, I though I end my post with one of my all time favourite features in QGIS.
I do not know enough of ArcGIS expression builder to really criticize it. But, AFAIK, you can use it to create labels and to populate a field using the field calculator. I know that there are many functions that you can use (I have used just a few) but they are not visible to the common user (you probably need to consult the ArcGIS Desktop Help to know them all). And you can create your own functions in VBScript, Python, and JsScript.
On QGIS side, like I said before, the Expression Builder can be used almost everywhere, and this makes it very convenient for many different purposes. In terms of functions, you have hundreds of functions right there in the builder’s dialog, with the corresponding syntax help, and some examples. You also have the fields and values like in ArcGIS, and you even have a “recent expressions” group for re-using recent expressions with no the need to remember prior expression.
Besides, you can create your own functions using Python (no VBScript or JsScript). For this purpose, you have a separate tab with a function editor. The editor have code highlighting and save your functions in your user area, making it available for later use (even for other QGIS sessions).
Conclusion
These are certainly not the only QGIS features that I miss, and they are probably not the most limiting ones (for instance, not being able to fully work with Spatialite and Postgis databases will make, for sure, my life miserable in the near future), but they were the ones I noticed right away when I (re)open ArcGIS for the first time.
I also feel that, based on the QGIS current development momentum, with each QGIS Changelog, the list will grow very fast. And although I haven’t tested ArcGIS Pro, I don’t think ESRI will be able to keep the pace.
“Are there things I still miss from ArcGIS?” Sure. I miss CMYK color support while exporting maps, for instance. But not as much as I miss QGIS now. Besides, I know that those will be addressed sooner or later.
In the end, I kinda enjoyed the opportunity to go back to ArcGIS, as it reinforced the way I think about QGIS. It’s all about freedom! Not only the freedom to use the software (that I was already aware) but also the freedom to control software itself and it’s outputs. Maintaining the users friendliness for new users, a lot have been done to make power users life easier, and they feel very pleased with it (at least I am).
With the release of the first long term release (2.8 LTR), and two other stable versions (2.10 and 2.12), 2015 was a great (and busy) year for the QGIS community, with lots of improvements and new features landing on QGIS source code.
As a balance, I have asked users to choose wich were their favorite new features during 2015 (from the visual changelogs list). As a result I got the following Top 5 features list.
5 – Python console improvements (2.8)
Since QGIS 2.8, we can drag and drop python scripts into QGIS window and they will be executed automatically. There is also a new a toolbar icon in the plugins toolbar and a shortcut ( Ctrl-Alt-P) for quick access to the python console.
4 – Processing new algorithms (2.8)
Also in QGIS 2.8, there were introduced some new algorithms to the processing framework. If you are into spatial analysis this must have done your day (or year).
Regular points algorithm
Symmetrical difference algorithm
Vector split algorithm
Vector grid algorithm
Hypsometric curves calculation algorithm
Split lines with lines
Refactor fields attributes manipulation algorithm
3 – Show rule-based renderer’s legend as a tree (2.8)
There were introduced a few nice improvements to QGIS legend. Version 2.8 brought us a tree presentation for the rule-based renderer. Better still, each node in the tree can be toggled on/off individually providing for great flexibility in which sublayers get rendered in your map.
2 – Advanced digitizing tools (2.8)
If you ever wished you could digitize lines exactly parallel or at right angles, lock lines to specific angles and so on in QGIS? Since QGIS 2.8 you can! The advanced digitizing tools are a port of the CADinput plugin and adds a new panel to QGIS. The panel becomes active when capturing new geometries or geometry parts.
1 – Rule-based labeling (2.12)
This was a very awaited feature (at least by me), and it was voted by the majority of users. Since 2.12, you can style features labels using rules. This gives us even more control over placement and styling of labels. Just like the rule based cartographic rendering, label rules can be nested to allow for extremely flexible styling options. For example, you can render labels differently based on the size of the feature they will be rendered into (as illustrated in the screenshot).
There were other new features that also made the delight of many users. For example, the Improved/consistent projection selection (2.8), PostGIS provider improvements (2.12), Geometry Checker and Geometry Snapper plugins (2.12), and Multiple styles per layer (2.8).
Don’t agree with this list? You can still cast your votes. You can also check the complete results in here.
Obviously, this list means nothing at all. I was a mere exercise as with such a diverse QGIS crowd it would be impossible to build a list that would fit us all. Besides, there were many great enhancements, introduced during 2015, that might have fallen under the radar for most users. Check the visual changelogs for a full list of new features.
On my behalf, to all developers, sponsors and general QGIS contributors,
Today I needed to create a view in PostGIS that returned the vertexes of a multi-polygon layer. Besides, I needed that they were numerically ordered starting in 1, and with the respective XY coordinates.
It seemed to be a trivial task – all I would need was to use the ST_DumpPoints() function to get all vertexes – if it wasn’t for the fact that PostGIS polygons have a duplicate vertex (the last vertex must be equal to the first one) that I have no interess in showing.
After some try-and-fail, I came up with the following query:
CREATE OR REPLACE VIEW public.my_polygons_vertexes AS
WITH t AS -- Transfor polygons in sets of points
(SELECT id_polygon,
st_dumppoints(geom) AS dump
FROM public.my_polygons),
f AS -- Get the geometry and the indexes from the sets of points
(SELECT t.id_polygon,
(t.dump).path[1] AS part,
(t.dump).path[3] AS vertex,
(t.dump).geom AS geom
FROM t)
-- Get all points filtering the last point for each geometry part
SELECT row_number() OVER () AS gid, -- Creating a unique id
f.id_polygon,
f.part,
f.vertex,
ST_X(f.geom) as x, -- Get point's X coordinate
ST_Y(f.geom) as y, -- Get point's Y coordinate
f.geom::geometry('POINT',4326) as geom -- make sure of the resulting geometry type
FROM f
WHERE (f.id_polygon, f.part, f.vertex) NOT IN
(SELECT f.id_polygon,
f.part,
max(f.vertex) AS max
FROM f
GROUP BY f.id_polygon,
f.part);
The interesting part occurs in the WHERE clause, basically, from the list of all vertexes, only the ones not included in the list of vertexes with the maximum index by polygon part are showed, that is, the last vertex of each polygon part.
Here’s the result:
The advantage of this approach (using PostGIS) instead of using “Polygons to Lines” and “Lines to points” processing tools is that we just need to change the polygons layer, and save it, to see our vertexes get updated automatically. It’s because of this kind of stuff that I love PostGIS.
During my professional and personal life, I have worked with much different software, with all kinds of licenses. Most of them would be proprietary, closed and / or commercial code. So why devote my time and learning “exclusively” to Open Source?
Without going into detail about the differences between open source software and free software, there are several reasons why FOSS (Free and Open Source Software) interest me.
The first is obviously freedom. Be free to use the software in any context and for any purpose, without being limited by the costs of software acquisition and / or the rules and conditions imposed by the manufacturer (as many said free (as beer) software do). That allows me to, for example, familiarize myself with its features without having to use piracy, or, as a freelancer worker, develop my work based on my technical capacities rather than my financial ones.
Second, the community and collaborative factor. The fact that open source software is built by user and for users, where the main goal is to enhance the software functionality (and not just raise the number of sales), and wherein each enhancement introduced by an individual or company is subsequently shared for the benefit of the whole community, avoiding duplication and “reinventing the wheel”. This is done in part through a lot of volunteer work and constant sharing of knowledge, either by the programmers or users. Thus, together, we all evolve at the same time as the software itself. In addition, everyone can contribute in some way, by producing code, writing and preparing supporting documentation, translating them into other languages or just by reporting bugs.
Finally, the “costs“. The adoption of open source software in enterprises (including the public ones), allow them to focus their investments in training of the human resources and the possible (and desirable) sponsoring of new features that are essential for their workflow, usually for a small portion of the values to spend on the acquisition of commercial software (that usually “forces” the purchase of features that may never be used).
In my last post, I have tried to show how I used QGIS 2.6 to create a map series where the page’s orientation adapted to the shape of the atlas features. This method is useful when the final scale of the maps is irrelevant, or when the size of the atlas elements is similar, allowing one to use a fixed scale. On the other hand, when using a fixed scale is mandatory and the features size are too different, it is needed to change the size of the paper. In this second part ot the post, I will try to show how I came to a solution for that.
As a base, I used the map created in the previous post, from which I did a duplicate. To exemplify the method, I tried to create a map series at 1:2.000.000 scale. Since I was going to change both width and height of the paper, I did not need to set an orientation, and therefore, I deactivated the data defined properties of the orientation option:
ith some maths with the map scale, the size of the atlas feature and the already defined margins, I came up with the following expressions to use, respectively, in width and height:
Allow me to clarify. (bounds_width( $atlasgeometry ) / 2000000.0) is the atlas feature’s width in meters when represented at 1:2.000.000. This is multiplied by 1000 to convert it to millimeters (the composer’s settings units). In order to keep the atlas feature not to close to the margin, I have decided to add 10% of margin around it, hence the multiplication by 1.1. To finish I add the map margins value that were already set in the previous post (i.e.,20 mm, 5 mm, 10 mm, 5 mm)
As one can see from the previous image, after setting the expressions in the paper width and height options, it’s size already changed according to the size of the atlas features. But, as expected, all the itens stubbornly kept their positions.For that reason, it has been necessary to change the size and position expressions for each of then.
Starting by the map item size, the expressions to use in width and height were not difficult to understand since they would be the paper size without the margins size:
To position the items correctly, all was needed was to replace the “CASE WHEN … THEN … END” statement by the expressions defined before. For instance, the expressions used in the X and Y options for the legend position:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 297 ELSE 210 END) - 7
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 210 ELSE 297 END) - 12
Changing the expressions of the X and Y position options for the remaining composer’s items I have reached the final layout.
Once again, printing/exporting all (25) maps was only one click away.
Since QGIS allows exporting the composer as georeferenced images, opening all maps in QGIS I got this interesting result.
As one can see by the results, using this method, we can get some quite strange formats. That is why in the 3rd and last post of this article, I will try to show how to create a fixed scale map series using standard paper formats (A4, A3, A2, A1 e A0).
Disclaimer: I’m not an English native speaker, therefore I apologize for any errors, and I will thank any advice on how to improve the text.
Tive necessidade de, numa camada de polígonos, adicionar colunas à tabela de atributos com as coordenadas dos centroides das geometria. Cheguei às seguintes expressões para calcular as coordenadas X e Y, respectivamente:
I had the need to add columns with the coordinates of polygons centroids. I came up with the following expressions to calculate X e Y, respectively:
A expressão parece bastante banal, mas ainda demorei a perceber que, não existindo funções x(geometry) e y(geometry), podia usar as funções xmin() e ymin() para obter as coordenadas dos centroides dos polígonos. Uma vez que esta não foi a primeira vez que precisei de usar estas expressões, fica agora o registo para não me voltar a esquecer.
The expression seems quite simple, but it toke me some time before I realize that, not having a x(geometry) and y(geometry) functions, I could use the xmin() and ymin() to get the coordinates of the polygons centroids. Since this wasn’t the first time I had to use this expressions, this post will work as a reminder for the future.
De quando em vez aparecem-me zonas com demasiado símbolos no mesmo local, e pensei como seria fantástico se os pudesse arrastar para um local mais conveniente sem ter de alterar as suas geometrias, tal como é possível fazer com as etiquetas. Esse pensamento deu-me a ideia base para a dica que vou demonstrar.
Now and then I get too many map symbols (points) in the same place, and I thought how nice it would be if we could drag n’ drop them around without messing with their geometries position, just like we do with labels. That thought gave me an idea for a cool hack.
Escolha a sua camada de pontos e comece por criar dois novos campos chamados symbX e symbY (Tipo: Decimal; Tamanho: 20; precisão: 5). No separador “Estilo” das propriedades da camada, defina para cada nível do seu símbolo o seguinte: Escolher “unidade do mapa” como a unidade para as opções de afastamento; Usar a seguinte expressão na opção afastamento das propriedades definidas por dados.
Choose your point layer and start by creating two new fields called symbX and symbY (Type: Decimal number; Size: 20; Precision: 5). Now go the layer properties and in the Style tab edit your symbol. For each level of your symbol select “map units” as the offset units, and set the following expression in the offset data define properties option:
CASE WHEN symbX IS NOT NULL AND symbY IS NOT NULL THEN
tostring($x - symbX) + ',' + tostring($y - symbY)
ELSE
'0,0'
END
Tenha atenção que, se as coordenadas do seu mapa tiver valores negativos, será necessário uma pequena alteração ao código. E. g., se tiver valores negativos em X deverá usar-se antes a expressão “tostring(symbX -$x)”.
Beware that if your coordinates have negative values you need to adapt the code. E.g., If you have negative values in X you should use “tostring(symbX -$x)” instead.
De forma temporária coloque etiquetas na sua camada usando um texto pequeno (eu usei o ‘+’ (sinal de mais) centrado e com um buffer branco) e defina as coordenadas X e Y dos propriedades definidadas por dados usando os campos symbX e symbY,
Now, temporarly label your layer with a small convenient text (I used a centered ‘+’ (plus sign) with a white buffer) and set its coordinates to data defined using the symbX and symbY Fields.
A partir desse momento, quando usar a ferramenta de mover etiquetas, não só alterará a posição da etiqueta, mas também a do próprio símbolo! Fantástico, não?
From this point on, when you use the move label tool, not only the label position change but also the actual symbol! Pretty cool, isn’t it?
Note que as geometria dos elementos não são alteradas durante o processo. Para além disso, lembre-se que neste caso também poderá adicionar linhas de guia para ligar os símbolos à posição original do ponto.
Notice that the features geometries are not changed during the process. Also, remember that in this case you can also add leading lines to connect the symbols to the original position of the points.
Now and then I get too many map symbols (points) in the same place, and I thought how nice it would be if we could drag n’ drop them around without messing with their geometries position, just like we do with labels. That thought gave me an idea for a cool hack.
Choose your point layer and start by creating two new fields called symbX and symbY (Type: Decimal number; Size: 20; Precision: 5). Now go the layer properties and in the Style tab edit your symbol. For each level of your symbol select “map units” as the offset units, and set the following expression in the offset data define properties option:
CASE WHEN symbX IS NOT NULL AND symbY IS NOT NULL THEN
tostring($x - symbX) + ',' + tostring($y - symbY)
ELSE
'0,0'
END
Be aware that, if your coordinates have negative values, you need to adapt the code. E.g., If you have negative values in X you should use “tostring(symbX -$x)” instead.
Now, temporarly label your layer with a small convenient text (I used a centered ‘+’ (plus sign) with a white buffer) and set its coordinates to data defined using the symbX and symbY Fields.
From this point on, when you use the move label tool, not only the label position change but also the actual symbol! Pretty cool, isn’t it?
Notice that the features geometries are not changed during the process. Also, remember that in this case you can also add leading lines to connect the symbols to the original position of the points.
The expression seems quite simple, but it toke me some time before I realize that, not having a x(geometry) and y(geometry) functions, I could use the xmin() and ymin() to get the coordinates of the polygons centroids. Since this wasn’t the first time I had to use this expressions, this post will work as a reminder for the future.
Recently I had the need to add labels to features with very close geometries, resulting in their collision.
Using data-defined override for label’s position (I have used layer to labeled layer plugin to set this really fast) and the QGIS tool to move labels, it was quite easy to relocate them to better places. However, in same cases, it was difficult to understand to which geometry they belonged.
I needed some kind of leading lines to connect, whenever necessary, label and feature. I knew another great plugin called “Easy Custom Labeling“, by Regis Haubourg, that did what I needed, but it would create a memory duplicate of the original layer, wish meant that any edition on the original layer wouldn’t be updated in the labels.
Since the data were stored in a PostgreSQL/Postgis database, I have decided to create a query that would return a layer with leading lines. I used the following query in DB manager:
SELECT
gid,
label,
ST_Makeline(St_setSRID(ST_PointOnSurface(geom),27493), St_setSRID(St_Point(x_label::numeric, y_label::numeric),27493))
FROM
epvu.sgev
WHERE
x_label IS NOT NULL AND
y_label IS NOT NULL AND
NOT ST_Within(ST_Makeline(St_setSRID(ST_PointOnSurface(geom),27493), St_setSRID(St_Point(x_label::numeric, y_label::numeric),27493)),geom))
This query creates a line by using the feature centroid as starting point and the label coordinate as end point. The last condition on the WHERE statement assures that the lines are only created for labels outside the feature.
With the resulting layer loaded in my project, all I need is to move my labels and save the edition (and press refresh) to show a nice leading line.
As always, the new QGIS version (QGIS 2.6 Brigthon) brings a vast new set of features that will allow the user to do more, better and faster than with the earlier version. One of this features is the ability to control some of the composer’s items properties with data (for instance, size and position). Something that will allow lots of new interesting usages. In the next posts, I propose to show how to create map series with multiple formats.
In this first post, the goal is that, keeping the page size, the map is created with the most suitable orientation (landscape or portrait) to fit the atlas feature. To exemplify, I will be using the Alaska’s sample dataset to create a map for each of Alaska’s regions.
I have started by creating the layout in one of the formats, putting the items in the desired positions.
To control the page orientation with the atlas feature, in the composition tab, I used the following expression in the orientation data defined properties:
CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry ) THEN 'landscape' ELSE 'portrait' END
Using the atlas preview, I could verify that the page’s orientation changed according to the form of the atlas feature. However, the composition’s items did not follow this change and some got even outside the printing area
To control both size and position of the composition’s items I had in consideration the A4 page size (297 x 210 mm), the map margins ( 20 mm, 5 mm, 10 mm, 5 mm) and the item’s reference points.
For the map item, using the upper left corner as reference point, it was necessary to change it’s height and width. I knew that the item height was the subtraction of the top and bottom margins (30 mm) from the page height, therefore I used the following expression:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 297 ELSE 210 END) - 30
Likewise, the expression to use in the width was:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 210 ELSE 297 END) - 10
The rest of the items were always at a relative position of the page without the need to change their size and therefore only needed to control their position. For example, the title was centered at the page’s top, and therefore, using the top-center as reference point, all that was needed was the following expression for the X position:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 297 ELSE 210 END) / 2.0
On the other hand, the legend needed to change the position in both X and Y. Using the bottom-right-corner as reference point, the X position expression was:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 297 ELSE 210 END) - 7
And for the Y position:
(CASE WHEN bounds_width( $atlasgeometry ) >= bounds_height( $atlasgeometry) THEN 210 ELSE 297 END) - 12
For the remaining items (North arrow, scalebar, and bottom left text), the expression were similar to the ones already mentioned, and, after setting them for each item, I got a layout that would adapt to both page orientation.
From that point, printing/exporting all (25) maps was one click away.
In the next post of the series, I will try to explain how to create map series where it’s the size of the page that change to keep the scale’s value of the scale constant.
Some time ago in the qgis-pt mailing list, someone asked how to show the coordinates of a map corners using QGIS. Since this features wasn’t available (yet), I have tried to reach a automatic solution, but without success, After some thought about it and after reading a blog post by Nathan Woodrow, it came to me that the solution could be creating a user defined function for the expression builder to be used in labels in the map.
Closely following the blog post instructions, I have created a file called userfunctions.py in the .qgis2/python folder and, with a help from Nyall Dawson I wrote the following code.
from qgis.utils import qgsfunction, iface
from qgis.core import QGis
@qgsfunction(2,"python")
def map_x_min(values, feature, parent):
"""
Returns the minimum x coordinate of a map from
a specific composer.
"""
composer_title = values[0]
map_id = values[1]
composers = iface.activeComposers()
for composer_view in composers():
composer_window = composer_view.composerWindow()
window_title = composer_window.windowTitle()
if window_title == composer_title:
composition = composer_view.composition()
map = composition.getComposerMapById(map_id)
if map:
extent = map.currentMapExtent()
break
result = extent.xMinimum()
return result
After running the command import userfunctions in the python console (Plugins > Python Console), it was already possible to use the map_x_min() function (from the python category) in an expression to get the minimum X value of the map.
All I needed now was to create the other three functions, map_x_max(), map_y_min() and map_y_max(). Since part of the code would be repeated, I have decided to put it in a function called map_bound(), that would use the print composer title and map id as arguments, and return the map extent (in the form of a QgsRectangle).
from qgis.utils import qgsfunction, iface
from qgis.core import QGis
def map_bounds(composer_title, map_id):
"""
Returns a rectangle with the bounds of a map
from a specific composer
"""
composers = iface.activeComposers()
for composer_view in composers:
composer_window = composer_view.composerWindow()
window_title = composer_window.windowTitle()
if window_title == composer_title:
composition = composer_view.composition()
map = composition.getComposerMapById(map_id)
if map:
extent = map.currentMapExtent()
break
else:
extent = None
return extent
With this function available, I could now use it in the other functions to obtain the map X and Y minimum and maximum values, making the code more clear and easy to maintain. I also add some mechanisms to the original code to prevent errors.
@qgsfunction(2,"python")
def map_x_min(values, feature, parent):
"""
Returns the minimum x coordinate of a map from a specific composer.
Calculations are in the Spatial Reference System of the project.
<h2>Syntax</h2>
map_x_min(composer_title, map_id)
<h2>Arguments</h2>
composer_title - is string. The title of the composer where the map is.
map_id - integer. The id of the map.
<h2>Example</h2>
map_x_min('my pretty map', 0) -> -12345.679
"""
composer_title = values[0]
map_id = values[1]
map_extent = map_bounds(composer_title, map_id)
if map_extent:
result = map_extent.xMinimum()
else:
result = None
return result
@qgsfunction(2,"python")
def map_x_max(values, feature, parent):
"""
Returns the maximum x coordinate of a map from a specific composer.
Calculations are in the Spatial Reference System of the project.
<h2>Syntax</h2>
map_x_max(composer_title, map_id)
<h2>Arguments</h2>
composer_title - is string. The title of the composer where the map is.
map_id - integer. The id of the map.
<h2>Example</h2>
map_x_max('my pretty map', 0) -> 12345.679
"""
composer_title = values[0]
map_id = values[1]
map_extent = map_bounds(composer_title, map_id)
if map_extent:
result = map_extent.xMaximum()
else:
result = None
return result
@qgsfunction(2,"python")
def map_y_min(values, feature, parent):
"""
Returns the minimum y coordinate of a map from a specific composer.
Calculations are in the Spatial Reference System of the project.
<h2>Syntax</h2>
map_y_min(composer_title, map_id)
<h2>Arguments</h2>
composer_title - is string. The title of the composer where the map is.
map_id - integer. The id of the map.
<h2>Example</h2>
map_y_min('my pretty map', 0) -> -12345.679
"""
composer_title = values[0]
map_id = values[1]
map_extent = map_bounds(composer_title, map_id)
if map_extent:
result = map_extent.yMinimum()
else:
result = None
return result
@qgsfunction(2,"python")
def map_y_max(values, feature, parent):
"""
Returns the maximum y coordinate of a map from a specific composer.
Calculations are in the Spatial Reference System of the project.
<h2>Syntax</h2>
map_y_max(composer_title, map_id)
<h2>Arguments</h2>
composer_title - is string. The title of the composer where the map is.
map_id - integer. The id of the map.
<h2>Example</h2>
map_y_max('my pretty map', 0) -> 12345.679
"""
composer_title = values[0]
map_id = values[1]
map_extent = map_bounds(composer_title, map_id)
if map_extent:
result = map_extent.yMaximum()
else:
result = None
return result
The functions became available to the expression builder in the “Python” category (could have been any other name) and the functions descriptions are formatted as help texts to provide the user all the information needed to use them.
Using the created functions, it was now easy to put the corner coordinates in labels near the map corners. Any change to the map extents is reflected in the label, therefore quite useful to use with the atlas mode.
The functions result can be used with other functions. In the following image, there is an expression to show the coordinates in a more compact way.
There was a setback… For the functions to become available, it was necessary to manually import them in each QGIS session. Not very practical. Again with Nathan’s help, I found out that it’s possible to import python modules at QGIS startup by putting a startup.py file with the import statements in the .qgis2/python folder. In my case, this was enough.
import userfunctions
I was pretty satisfied with the end result. The ability to create your own functions in expressions demonstrates once more how easy it is to customize QGIS and create your own tools. I’m already thinking in more applications for this amazing functionality.
You can download the Python files with the functions HERE. Just unzip both files to the .qgis2/python folder, and restart QGIS, and the functions should become available.
Disclaimer: I’m not an English native speaker, therefore I apologize for any errors, and I will thank any advice on how to improve the text.
Trata-se de um cenário muito recorrente em análise espacial. Tendo uma camada\tabela composta por diversos polígonos, queremos “juntá-los” de acordo com valores distintos de um ou mais atributos (exemplo: de uma camada com os limites de freguesias, queremos obter os concelhos, ou, da COS ao 3º nível, obter o 2º ou o 1º)
Este artigo tem como objectivo mostrar como fazê-lo em Postgres\Postgis.
Tabela de exemplo
Como exemplo vou usar uma tabela como o seguinte formato:
CREATE TABLE tabela_1
(gid serial PRIMARY KEY,
campo1 character varying(128),
campo2 integer,
geom geometry(MultiPolygon,27493);
Dissolver todos os polígonos
Em primeiro lugar podemos simplesmente agregar todos os elementos num multi-polígono único. Para tal usamos a função ST_Union().
SELECT
ST_Union(t.geom) as geom
FROM
tabela_1 as t;
Separar polígonos que não sejam contíguos
Se por outro lado não quisermos que o resultado apresente multi-polígonos usamos a função ST_Dump() recolhendo o campo da geometria.
SELECT
(ST_Dump(ST_Union(t.geom))).geom as geom
FROM
tabela_1 as t;
Dissolver polígonos com base em valores dos campos
Se quisermos dissolver os polígonos que tenham valores iguais num ou mais campos, basta incluí-los na cláusula GROUP BY. Se quisermos que esses campos apareçam no resultado (geralmente queremos) há que referi-los no início do SELECT.
SELECT
campo1,
campo2,
(ST_Dump(ST_Union(t.geom))).geom as geom
FROM
tabela_1 as t
GROUP BY
campo1,
campo2;
Nota 1: Para quem prefere usar interfaces gráficos, preencher formulários e clicar em botões, o uso de SQL para fazer este tipo de operações pode parecer demasiado complicado e até um pouco retrógrado. Mas uma coisa garanto, com alguma prática as dificuldades iniciais são ultrapassadas e os benefícios que se retiram deste tipo de abordagem são muito recompensadores.
Nota 2: Visualizar o resultado deste tipos consultas de agregação (que usam a cláusula GROUP BY) no QGIS pode ser desafiante, este artigo explica como ultrapassar essa dificuldade.
I have finally “finished” my new plugin. I uses some quotation marks, since I believe that there is still space for a few improvement. This plugin arised with the need to calculate the travel time for the Cascais oficial pedestrian routes, and started as a simple python script. I have then decided to create a graphic interface and publish it as a plugin in the hope that someone else finds it useful.
Walking time is a QGIS python plugin that uses Tobbler’s hiking function to estimate the travel time along a line depending on the slope.
The input data required are a vector layer with lines and a raster layer with elevation values (1). One can adjust the base velocity (on flat terrain) according to the type of walking or walker. By default, the value used is 5 km h (2). The plugin update or create fields with estimated time in minutes in forward and in reverse direction (3). One can run the plugin for all elements of the vector layer, or only on selected routes (4).
The plugin can also been used to prepare a network (graph) to perform network analysis when the use of travel walking time as cost is intended.
Inspired in a post by Anita Graser, I’ve tried to use QGIS to create a Cascais‘s old looking map, as if it have been drawn by hand in a methodical way.
Defining the styles
I have started by defining the styles for each elements to represent.
Buildings
To fill the buildings, I have tried to use a color that reminds me the portuguese roofs, similar to the color commonly used in old maps of cities, with a slightly darker outline of the same color.
To give a bit of dimension, a shadow was created beneath, using a “simple fill” with dark colors and using a Offset X,Y. The values were chosen assuming the predominant direction of building’s facades, so that the effect could be seen all over the map area.
Green spaces
For the green spaces, 3 symbol layers were used. One with a green “simple fill”. A second one with a thick outline (outline: simple line) in a darker green, and using the new 2.2 functionality that allows one to show outlines only in the polygons inside.
The last symbol layer is just a tin line of a green even darker than the other two.
The Sea
For the sea, the same effect as the green spaces was used, but in blues and with the middle outline even thicker.
Roads
In the road, it was used a thick line with a orange pastel color. Some street names labels were created on top of the line using a script font (in have used Pristina Bold). To improve the label readability, a small white buffer with 50% transparency was added.
Beach
In the beaches, besides a simple fill as background, a point patern fill was used with a very small dot.
Map composing
Though the map is looking almost done, it’s in the print composer that the final touches are given. First, the map sheet is totally covered with an image of an old papel (the same used by Anita). A bit of transparency is added (20%), so that the effect is not too strong.
Alterwards, the actual map is added, and in the map item properties, the rendering mode is changed from “normal” (by default) to “multiply”. This way it looks like if the map was draw directly on the old paper.
After this, it’s all about adding a few more labels (the beach and places names), a north arrow and the graphic scale (always using “multiply” rendering mode), and… Voilá, we have a map!
Quando através de uma consulta SQL a uma base de dados postgres\postgis se procede a uma agregação (através do uso da cláusula GROUP BY) é quase certo perder a chave primária da tabela original (geralmente o gid). No entanto, para visualizar o resultado de consultas SQL em QGIS é necessário que exista um campo com valores inteiros distintos para usar como identificadores únicos. Assim, para ultrapassar este contratempo, há que criar uma coluna com essas características.
Essa coluna pode ser feita usando a função ROW_NUMBER(), da seguinte forma:
WITH r as (SELECT
campo1,
(ST_Dump(ST_Union(t.geom))).geom as geom
FROM
tabela_1 as t
GROUP BY
campo1)
SELECT
ROW_NUMBER() OVER() as id,
r.*
FROM r;
Copiando toda para a expressão na janela SQL do DB Manager (Base de dados > Gestor BD > Janela SQL), é possível usar o campo id como identificador único.
Este tipo de mapas pode ser feito em QGISs usando a uma combinação da transparência e cor dos símbolos e o blending mode dos elementos.
Note-se a diferença entre a transparência e blending mode da camada (que é aplicado a toda a camada) e a transparência do símbolo e blending dos elementos (que acumulam com outros elementos da mesma camada).
Esta opções estão disponíveis em Propriedades da camada > Estilo.
Com um valor de transparência do símbolo de 95%, a cor do elemento tornar-se à totalmente opaca quando pelo menos 20 elementos de sobrepuserem. Este número é limitado à sobreposição de 100 elementos(tranparencia 99%).
Usando diferentes modos de blending (como a multiplicação ou a adição) consegues-se obter outros efeitos.
Duplicando a camada, usando diferentes cores (no exemplo abaixo o verde para uma camada e o vermelho para a imediatamente baixo) e usando blending mode dogde,consegue-se obter efeitos ainda mais interessantes.
Em altura de testes à versão em desenvolvimento do QGIS (versão master), dá jeito ter também instalada a última versão estável do QGIS. Em windows isso não representa um problema, uma vez que se podem instalar várias versões do QGIS em paralelo (tanto via Osgeo4w como standalone). Em linux, o processo não é tão directo pelo facto da instalação se realizar por obtenção de diversos pacotes disponíveis nos repositórios, não sendo por isso possível instalar mais do que uma versão sem que se originem quebras de dependências. Assim, instalando a versão estável através dos repositórios, as alternativas para instalação da versão em desenvolvimento são:
Compilar o QGIS master do código fonte;
Instalar o QGIS master num docker;
Instalar o QGIS master numa máquina virtual;
Neste artigo vou mostrar como compilar o código fonte em Ubuntu 14.04. Afinal não é tão difícil quanto parece. Meia dúzia de comandos e um pouco de paciência e vai-se lá. Usei como base as indicações do ficheiro INSTALL.TXT disponível no código fonte com umas pequenas alterações.
Instalar todas as dependências necessárias
Num terminal correr o seguinte comando para instalar todas as dependências e ferramentas necessárias à compilação do QGIS. (adicionei o ccmake e o git ao comando original)
O código fonte pode ser colocado numa pasta à escolha de cada um. Seguindo a sugestão do ficheiro de instruções acabei por colocar tudo na minha pasta home/alexandre/dev/cpp.
mkdir -p ${HOME}/dev/cpp
cd ${HOME}/dev/cpp
Já dentro da pasta home/alexandre/dev/cpp, podemos obter o código do qgis executando o seguinte comando git:
git clone git://github.com/qgis/QGIS.git
Nota: Se pretendesse fazer alterações ao código e experimentar se funcionava, então deveria fazer o clone do fork do qgis do meu próprio repositório, ou seja:
O código fonte tem de ser compilado e instalado em locais próprios para evitar conflitos com outras versões do QGIS. Por isso, há que criar uma pasta para efectuar a instalação:
mkdir -p ${HOME}/apps
E outra onde será feita a compilação:
cd QGIS
mkdir build-master
cd build-master
Configuração
Já na pasta build-master damos início ao processo de compilação. O primeiro passo é a configuração, onde vamos dizer onde queremos instalar o QGIS master. Para isso executamos o seguinte comando (não esquecer os dois pontos):
ccmake ..
Na configuração é necessário alterar o valor do CMAKE_INSTALL_PREFIX que define onde vai ser feita a instalação, no meu caso usei a pasta já criada ‘home/alexandre/apps’ . Para editar o valor há que mover o cursor até à linha em causa e carregar em [enter], depois de editar, volta-se a carregar em [enter]. Depois há que carregar em [c] para refazer a configuração e depois em ‘g’ para gerar a configuração.
Compilação e instalação
Já com tudo configurado resta compilar o código e depois instalá-lo:
make
sudo make install
Nota: Estes dois passos podem demorar um bocadinho, principalmente na primeira vez que o código for compilado.
Depois de instalado podemos correr o QGIS master a partir da pasta de instalação:
cd ${HOME}/apps/bin/
export LD_LIBRARY_PATH=/home/alexandre/apps/lib
export QGIS_PREFIX_PATH=/home/alexandre/apps
${HOME}/apps/bin/qgis
Para se tornar mais cómodo, podemos colocar os últimos 3 comandos num ficheiro .sh e gravá-lo num local acessível (desktop ou home) para executarmos o qgis sempre que necessário.
UPDATE: Actualizar a versão master
Como já foi referido num comentário, a versão em desenvolvimento está constantemente a ser alterada, por isso para testar se determinados bugs foram entretanto corrigidos há que a actualizar. Trata-se de um processo bastante simples. O primeiro passo é actualizar o código fonte:
cd ${HOME}/dev/cpp/qgis
git pull origin master
E depois é voltar a correr a compilação (que desta feita será mais rápida):
