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Wed Jul 1 07:45:09 2015

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QGIS Planet

A interactive command bar for QGIS

Something that has been on my mind for a long time is a interactive command interface for QGIS.  Something that you can easily open, run simple commands, and is interactive to ask for arguments when they are needed.

After using the command interface in Emacs for a little bit over the weekend – you can almost hear the Boos! from heavy Vim users :) – I thought this is something I must have in QGIS as well.  I’m sure it can’t be that hard to add.

So here it is.  A interactive command interface for QGIS.

commandbar

commandbar2

The command bar plugin (find it in the plugin installer) adds a simple interactive command bar to QGIS. Commands are defined as Python code and may take arguments.

Here is an example function:

@command.command("Name")
def load_project(name):
    """
    Load a project from the set project paths
    """
    _name = name
    name += ".qgs"
    for path in project_paths:
        for root, dirs, files in os.walk(path):
            if name in files:
                path = os.path.join(root, name)
                iface.addProject(path)
                return
    iface.addProject(_name)

All functions are interactive and if not all arguments are given when called it will prompt for each one.

Here is an example of calling the point-at function with no args. It will ask for the x and then the y

pointat

Here is calling point-at with all the args

pointatfunc

Functions can be called in the command bar like so:

my-function arg1 arg2 arg2

The command bar will split the line based on space and the first argument is always the function name, the rest are arguments passed to the function. You will also note that it will convert _ to - which is easier to type and looks nicer.

The command bar also has auto complete for defined functions – and tooltips once I get that to work correctly.

You can use CTRL + ; (CTRL + Semicolon), or CTRL + ,, to open and close the command bar.

What is a command interface without auto complete

autocomplete

Use Enter to select the item in the list.

How about a function to hide all the dock panels. Sure why not.

@command.command()
def hide_docks():
    docks = iface.mainWindow().findChildren(QDockWidget)
    for dock in docks:
        dock.setVisible(False)

alias command

You can also alias a function by calling the alias function in the command bar.

The alias command format is alias {name} {function} {args}

Here is an example of predefining the x for point-at as mypoint

-> alias mypoint point-at 100

point-at is a built in function that creates a point at x y however we can alias it so that it will be pre-called with the x argument set. Now when we call mypoint we only have to pass the y each time.

-> mypoint
(point-at) What is the Y?: 200

You can even alias the alias command – because why the heck not :)

-> alias a alias
a mypoint 100

a is now the shortcut hand for alias

WHY U NO USE PYTHON CONSOLE

The Python console is fine and dandy but we are not going for a full programming language here, that isn’t the point. The point is easy to use commands.

You could have a function called point_at in Python that would be

point_at(123,1331)

Handling incomplete functions is a lot harder because of the Python parser. In the end it’s easier and better IMO to just make a simple DSL for this and get all the power of a DSL then try and fit into Python.

It should also be noted that the commands defined in the plugin can still be called like normal Python functions because there is no magic there. The command bar is just a DSL wrapper around them.

Notes

This is still a bit of an experiment for me so things might change or things might not work as full expected just yet.

Check out the projects readme for more info on things that need to be done, open to suggestions and pull requests.

Also see the docs page for more in depth information


Filed under: Open Source, python, qgis Tagged: plugin, pyqgis, qgis

Crayfish 2.0: What's New!

Crayfish 2.0

After listening to user feedback we decided to do some major work on Crayfish. The changes include code refactoring, changes to the user interface, support for an additional file format, adding a vector and contour overlay, and a shiny new logo!

Read on for a look at some of the new features in more detail...

Time control

In the new version of Crayfish a time slider allows users to quickly browse through time. A drop-down menu allows the selection of an exact time.

Vector and contour overlay

In previous versions of Crayfish it was only possible to load contours and vectors from the same dataset. For example, it was not possible to show velocity vectors on top of depth contours. With the new Crayfish you can "unlock" the legend and choose different vectors or contours to be displayed. The video below demonstrates this in action.

Special times

Some datasets contain a special time-step outside the outputted time range. For example, Maximums and Minimums are stored at time 99999 in TUFLOW modelling package. Within the layer tree, additional time-steps items will now be shown if they exist within the dataset.

Additional file formats

We have added support for the XMDF file format. In addition, Hydro_AS 2D users should be able to open their files in the latest Crayfish.

New Python Module

We’ve refactored lots of code in the Crayfish library which makes it much easier to add support for further file formats and additional functionality. The Crayfish library now comes with a new Python module that allows easy manipulation with the mesh and results data – either in your custom scripts or within the QGIS Python console. For example, printing the coordinates of the nodes of a mesh together with their elevation takes just few lines of code:

import crayfish

m = crayfish.Mesh("/data/my_mesh.2dm")
o = m.dataset(0).output(0) # bed elevation data

for index, node in enumerate(m.nodes()):
print "Node XYZ: ", node.x, node.y, o.value(index)

New Profile tool plugin

If you use Profile tool plugin in QGIS, you can create a profile from the Crayfish layer and browse through the time. The profile gets updated as you change the output time.

Problems

If you have some feedback on our changes, suggestions for new functionality, or come across a bug, feel free to file a ticket on the issues page of the Crayfish github repository.

Sponsors

We’d like to thank Maroondah City Council for sponsoring some of the great features in this release.

Introducing QGIS live layer effects!

I’m pleased to announce that the crowdfunded work on layer effects for QGIS is now complete and available in the current development snapshots! Let’s dive in and explore how these effects work, and check out some of the results possible using them.

I’ll start with a simple polygon layer, with some nice plain styling:

Nice and boring polygon layer

A nice and boring polygon layer

If I open the properties for this layer and switch to the Style tab, there’s a new checkbox for “Draw effects“. Let’s enable that, and then click the little customise effects button to its right:

Enabling effects for the layer

Enabling effects for the layer

A new “Effects Properties” dialog opens:

Effects Properties dialog

Effects Properties dialog

You can see that currently the only effect listed is a “Source” effect. Source effects aren’t particularly exciting – all they do is draw the original layer unchanged. I’m going to change this to a “Blur” effect by clicking the “Effect type” combo box and selecting “Blur“:

Changing to a blur effect

Changing to a blur effect

If I apply the settings now, you’ll see that the polygon layer is now blurry. Now we’re getting somewhere!

Blurry polygons!

Blurry polygons!

Ok, so back to the Effects Properties dialog. Let’s try something a bit more advanced. Instead of just a single effect, it’s possible to chain multiple effects together to create different results. Let’s make a traditional drop shadow by adding a “Drop shadow” effect under the “Source” effect:

Setting up a drop shadow

Setting up a drop shadow

Effects are drawn top-down, so the drop shadow will appear below the source polygons:

Live drop shadows!

Live drop shadows!

Of course, if you really wanted, you could rearrange the effects so that the drop shadow effect is drawn above the source!..

Hmmmm

Hmmmm…

You can stack as many effects as you like. Here’s a purple inner glow over a source effect, with a drop shadow below everything:

Inner glow, source, drop shadow...

Inner glow, source, drop shadow…

Now it’s time to get a bit more creative… Let’s explore the “transform” effect. This effect allows you to apply all kinds of transformations to your layer, including scaling, shearing, rotation and translation:

The transform effect

The transform effect

Here’s what the layer looks like if I add a horizontally shearing transform effect above an outer glow effect:

Getting freaky...

Getting tricky…

Transforms can get really freaky. Here’s what happens if we apply a 180° rotation to a continents layer (with a subtle nod to xkcd):

Change your perspective on the world!

Change your perspective on the world!

Remember that all these effects are applied when the layers are rendered, so no modifications are made to the underlying data.

Now, there’s one last concept regarding effects which really blasts open what’s possible with them, and that’s “Draw modes“. You’ll notice that this combo box contains a number of choices, including “Render“, “Modify” and “Render and Modify“:

"Draw mode" options

“Draw mode” options

These draw modes control how effects are chained together. It’s easiest to demonstrate how draw modes work with an example, so this time I’ll start with a Transform effect over a Colorise effect. The transform effect is set to a 45° rotation, and the colorise effect set to convert to grayscale. To begin, I’ll set the transform effect to a draw mode of Render only:

The "Render only" draw mode

The “Render only” draw mode

In this mode, the results of the effect will be drawn but won’t be used to modify the underlying effects:

Rotation effect over the grayscale effect

Rotation effect over the grayscale effect

So what we have here is that the polygon is drawn rotated by 45° by the transform effect, and then underneath that there’s a grayscale copy of the original polygon drawn by the colorise effect. The results of the transform effect have been rendered, but they haven’t affected the underlying colorise effect.

If I instead set the Transform effect’s draw mode to “Modifier only” the results are quite different:

Rotation modifier for grayscale effect

Rotation modifier for grayscale effect

Now, the transform effect is rotating the polygon by 45° but the result is not rendered. Instead, it is passed on to the subsequent colorise effect, so that now the colorise effect draws a grayscale copy of the rotated polygon. Make sense? We could potentially chain a whole stack of modifier effects together to get some great results. Here’s a transform, blur, colorise, and drop shadow effect all chained together using modifier only draw modes:

A stack of modifier effects

A stack of modifier effects

The final draw mode, “Render and modify” both renders the effect and applies its result to underlying effects. It’s a combination of the two other modes. Using draw modes to customise the way effects chain is really powerful. Here’s a combination of effects which turn an otherwise flat star marker into something quite different:

Lots of effects!

Lots of effects!

The last thing I’d like to point out is that effects can be either applied to an entire layer, or to the individual symbol layers for features within a layer. Basically, the possibilities are almost endless! Python plugins can also extend this further by implementing additional effects.

All this work was funded through the 71 generous contributors who donated to the crowdfunding campaign. A big thank you goes out to you all whole made this work possible! I honestly believe that this feature takes QGIS’ cartographic possibilities to whole new levels, and I’m really excited to see the maps which come from it.

Lastly, there’s two other crowdfunding campaigns which are currently in progress. Lutra consulting is crowdfunding for a built in auto trace feature, and Radim’s campaign to extend the functionality of the QGIS GRASS plugin. Please check these out and contribute if you’re interested in their work and would like to see these changes land in QGIS.

GRASS GIS 6.4.5RC1 released

GRASS GIS logoAfter months of development a first release candidate of GRASS GIS 6.4.5 is now available. This is a stability release of the GRASS GIS 6 line.

Source code download:
http://grass.osgeo.org/grass64/source/
http://grass.osgeo.org/grass64/source/grass-6.4.5RC1.tar.gz

Binaries download:
http://grass.osgeo.org/download/software/#g64x

To get the GRASS GIS 6.4.5RC1 source code directly from SVN:
svn checkout http://svn.osgeo.org/grass/grass/tags/release_20150406_grass_6_4_5RC1

Key improvements:
Key improvements of the GRASS GIS 6.4.5RC1 release include stability fixes (esp. vector library), some fixes for wxPython3 support, some module fixes, and more message translations.

See also our detailed announcement:
http://trac.osgeo.org/grass/wiki/Release/6.4.5RC1-News

First time users should explore the first steps tutorial after installation:
http://grasswiki.osgeo.org/wiki/Quick_wxGUI_tutorial

Release candidate management at
http://trac.osgeo.org/grass/wiki/Grass6Planning

Please join us in testing this release candidate for the final release.

Consider to donate pizza or beer for the next GRASS GIS Community Sprint (following the FOSS4G Europe 2015 in Como):
http://grass.osgeo.org/donations/

Thanks to all contributors!

About GRASS GIS

The Geographic Resources Analysis Support System (http://grass.osgeo.org), commonly referred to as GRASS GIS, is an Open Source Geographic Information System providing powerful raster, vector and geospatial processing capabilities in a single integrated software suite. GRASS GIS includes tools for spatial modeling, visualization of raster and vector data, management and analysis of geospatial data, and the processing of satellite and aerial imagery. It also provides the capability to produce sophisticated presentation graphics and hardcopy maps. GRASS GIS has been translated into about twenty languages and supports a huge array of data formats. It can be used either as a stand-alone application or as backend for other software packages such as QGIS and R geostatistics. It is distributed freely under the terms of the GNU General Public License (GPL). GRASS GIS is a founding member of the Open Source Geospatial Foundation (OSGeo).

The GRASS Development Team, April 2015

The post GRASS GIS 6.4.5RC1 released appeared first on GFOSS Blog | GRASS GIS Courses.

Create great looking topographic maps in QGIS

Wicklow-Topo-original

In this tutorial I will show you how to create a Hillshaded topographic map in QGIS. We will be using Shuttle Radar Topography Mission (SRTM) data, a near global Digital Elevation Model (DEM) collected in February 2000 aboard NASA’s Space Shuttle Endeavour (mission STS-99). The mission used a X-Band mapping radar to measure the Earth’s topography, built in collaboration with the U.S. Jet Propulsion Laboratory, the U.S. National Imagery and Mapping Agency (now the National Geospatial-Intelligence Agency), and the German and Italian space agencies.

The raw radar data has been continuously processed and improved since it was first collected. Countless artefacts have been painstakingly removed and areas of missing data have been filled using alternate data sources. The version we will be using is the 1 Arc-Second Global SRTM dataset, an enhanced 30 meter resolution DEM that was released last year. It is a substantial improvement over the 3 Arc-Second / 90 meter SRTM data previously available for Ireland. SRTM elevation data can be downloaded from the United States Geological Survey’s EarthExplorer website.

When first loaded into QGIS (via Add Raster Layer), the DEM is displayed as a rather uninformative black and white image.

Wicklow-Topo-blackwhite

It is therefore necessary to apply a suitable colour ramp that accentuates topography. While it is possible to create your own colour ramp, or use one of the colour ramps provided by QGIS, superior colour ramps can be downloaded using Etienne Tourigny’s Color Ramp Manager (Plugins – Manage and Install Plugins). After the plugin is added to QGIS, go to the Plugins menu again and choose the Colour Ramp Manager.

In the window that pops up, choose the full opt-city package and click check for update. The plugin will then download the cpt-city library, a collection of over a hundred cartographic gradients (version 2.15). After the package downloads, quit the dialogue.

Back in QGIS, right click the DEM layer to bring up the Layer Properties dialogue. In the Style tab, change the render type from single band grey to single band pseudocolor. Then click new color ramp and new color ramp again, choose the cpt-city color ramp to bring up the cpt-city dialogue. Click topography and choose the sd-a colour ramp. While this is an excellent colour ramp, I find its colours are a bit too strong for my liking.

Still in the Layer Properties dialogue, change the min and max values to match your DEM’s lowest and highest elevations values and click classify, this applies the new colour ramp. Next, change the brightness to 30 and lower the contrast and saturation to -20. Click OK to apply the new style and quit the Layer Properties dialogue.

Wicklow-Topo-noShade

Next we need to create a Hillshade layer from the DEM, a 3D like visual representation of topographic relief. This is achieved via the menu Raster – Analysis – DEM (Terrain models). There is one small catch, the hillshading algorithm assumes the DEM’s horizontal units are in meters (they are decimal degrees). We need to enter a scale correction factor of 111120 (in the Scale ratio vert. units to horiz. box). Once that is all done, select an output path to save the generated hillshade and click OK. Generating a hillshade may take up to a minute depending on the size of your DEM.

Wicklow-Topo-hillshade

After the hillshade is created, open its Layer properties dialogue. Change the min and max values to 125 and 255, increase its brightness to 45 and contrast to 20. Finally, switch the blending mode from normal to multiply. This allows the DEM beneath the hillshade to show though. Click OK to apply the new style.

If you followed these steps correctly you will have created a fine looking topographic map similar to the one below. It’s also possible to create contours but that’s a tutorial for another day.

Wicklow-Topo

Technical note:

There are two hillshading algorithms available in QGIS, one by Horne (1981) and another by Zevenbergen and Thorne (1987). Jones (1998) examined the quality of hillshading algorithms, he found the algorithm of Fleming and Ho€er (1979) is slightly superior to Horne’s (1981) algorithm. Zevenbergen and Thorne’s (1987) algorithm is a derivation of Fleming and Ho€er’s (1979) formula. QGIS uses Horne’s (1981) algorithm by default.

References:

Horn, B.K., 1981. Hill shading and the reflectance map. Proceedings of the IEEE, 69, 14–47.

Jones, K.H., 1998. A comparison of algorithms used to compute hill slope as a property of the DEM [PDF]. Computers & Geosciences, 24, 315–323.

Zevenbergen, L.W. & Thorne, C.R., 1987. Quantitative analysis of land surface topography. Earth surface processes and landforms, 12, 47–56.

Time Manager 1.6 – now with feature interpolation

Over the last couple of weeks, Karolina has been very busy improving and expanding Time Manager. This post is to announce the 1.6 release of Time Manager which brings you many fixes and exciting new features.

Screenshot 2015-03-25 17.58.38

What’s this feature interpolation you’re talking about?

Interpolation is really helpful if you have multiple observations of the same (moving) real-world object at different points in time and you want to visualize the movement between the observations. This can be used to visualize animal paths, vehicle tracks, or any other movement in space.

The following example shows a simple layer which contains 12 point features (3 for each id value).

Screenshot 2015-03-25 17.50.55

Using Time Manager interpolation, it is easy to create animations with interpolated positions between observations:

animation

How is it done?

When you open the Time Manager 1.6 Settings | Add layer dialog, you will find a new option for interpolation settings. This first version supports linear interpolation of point features but more options might be added in the future. Note how the id attribute is specified to let Time Manager know which features belong to the same real-world object.

Screenshot 2015-03-25 17.43.08

For the interpolation, Time Manager creates a new layer which contains the interpolated features. You can see this layer in the layer list.

Screenshot 2015-03-25 17.46.13

I’m really looking forward to seeing all the great animations this feature will enable. Thanks Karolina for making this possible!


Inofficial QGIS 2.8 RPMs for EPEL 7: Fedora 20, Fedora 21, Centos 7, Scientific Linux 7

qgis-icon_smallThanks to the work of Devrim Gündüz, Volker Fröhlich, Dave Johansen, Rex Dieter and other Fedora/EPEL packagers I had an easy going to prepare RPM packages of QGIS 2.8 Wien for Fedora 20 and 21, Centos 7, and Scientific Linux 7.

The base SRPM package I copied from Fedora’s koji server, modified the SPEC file in order to remove the now outdated PyQwt bindings (see bugzilla) and compiled QGIS 2.8 via the great COPR platform.

Repo: https://copr.fedoraproject.org/coprs/neteler/QGIS-2.8-Wien/

The following packages can now be installed and tested on epel-7-x86_64 (Centos 7, Scientific Linux 7, etc.), Fedora-20-x86_64, and Fedora-21-x86_64:

  • qgis 2.8.1
  • qgis-debuginfo 2.8.1
  • qgis-devel 2.8.1
  • qgis-grass 2.8.1
  • qgis-python 2.8.1
  • qgis-server 2.8.1

Installation instructions (run as “root” user or use “sudo”):

# EPEL7:
yum -y install epel-release
yum -y install wget
# https://copr.fedoraproject.org/coprs/neteler/python-OWSLib/
wget -O /etc/yum.repos.d/neteler-python-OWSLib-epel-7.repo https://copr.fedoraproject.org/coprs/neteler/python-OWSLib/repo/epel-7/neteler-python-OWSLib-epel-7.repo
yum -y update
yum -y install python-OWSLib
wget -O /etc/yum.repos.d/qgis-epel-7.repo https://copr.fedoraproject.org/coprs/neteler/QGIS-2.8-Wien/repo/epel-7/neteler-QGIS-2.8-Wien-epel-7.repo
yum update
yum install qgis qgis-grass qgis-python qgis-server

# Fedora 20:
wget -O /etc/yum.repos.d/qgis-epel-7.repo https://copr.fedoraproject.org/coprs/neteler/QGIS-2.8-Wien/repo/fedora-20/neteler-QGIS-2.8-Wien-fedora-20.repo
yum update
yum install qgis qgis-grass qgis-python qgis-server

# Fedora 21:
wget -O /etc/yum.repos.d/qgis-epel-7.repo https://copr.fedoraproject.org/coprs/neteler/QGIS-2.8-Wien/repo/fedora-21/neteler-QGIS-2.8-Wien-fedora-21.repo
yum update
yum install qgis qgis-grass qgis-python qgis-server

The other packages are optional (well, also qgis-grass, qgis-python, and qgis-server…).

Enjoy!

PS: Of course I hope that QGIS 2.8 officially hits EPEL7 anytime soon! My COPR repo is just a temporary bridge towards that goal.

EDIT 30 April 2015:

  • updated EPEL7 installation for python-OWSLib dependency

The post Inofficial QGIS 2.8 RPMs for EPEL 7: Fedora 20, Fedora 21, Centos 7, Scientific Linux 7 appeared first on GFOSS Blog | GRASS GIS Courses.

In memory of Tim York

The other weekend the world lost a great guy, someone so nice that you struggle to find anything bad to say about him at all. Tim was only 27 but died tragically on the weekend, to the complete shock of everyone that knew him. I don’t think anyone really knew what to feel at that point, and even now it is still really hard to take it.

Tim was very well known in the GIS space here in Australia, and extremely well respected by everyone that knew him. I attended Locate15, where I was going catch up for a beer and chat with him, and almost everyone I talked to knew who he was and how great he really was. I would not doubt at all he could have become CEO or leader at a large company, no doubt at all.

It was mentioned at the funeral that we should try to think of how Tim made our lives better. For that I can fully thank Tim for my job at DMS. It was at a SSSI event after talking with my now manager about if they would like me at DMS that I had caught up with Tim and he encouraged me to move into the private sector. For that I thank him a lot.

I have started to read “How To Win Friends & Influence People” by Dale Carnegie, because one can always do with more skills in life, and some important points from the book:

  • Become genuinely interested in other people.
  • Smile.
  • Remember a person’s name.
  • Be a good listener. Encourage others to talk about themselves.
  • Talk in terms of the other person’s interests

This. All of this is what Tim did. This is the reason it always felt great to talk to him and be around him, even when I only saw him a few times.

I don’t know if Tim’s life was better for knowing me, given his large group of friends and great partner I suspect not, but I know sure as shit that mine was better for having known him.

319187_10150351976087518_3388507_n


Filed under: personal

Adding ESRI’s Online World Imagery Dataset to QGIS

ESRI’s ArcGIS Online World Imagery is a high resolution satellite and aerial imagery base map for use in Google Earth, ArcMap and ArcGIS Explorer. The same excellent imagery is used by the Bing Maps Aerial layer. Somewhat surprisingly, World Imagery can also be accessed by QGIS, as it supports ESRI’s map servers that use Representational State Transfer (REST) and Simple Object Assess Protocol (SOAP) standards.

Simply copy and past the following code into the Python Console in QGIS and press return (Plugins – Console):

qgis.utils.iface.addRasterLayer("http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer?f=json&pretty=true","raster")

The code adds an ESRI Online World Imagery base map to QGIS. It has a number of advantages over the popular OpenLayers Plugin that adds various Google, Bing and OpenStreetMap image layers to QGIS. Unlike images downloaded by the OpenLayers plugin the ESRI World Imagery base map is a true Raster who’s attributes are fully editable e.g. brightness, blending mode and transparency can be adjusted. World Imagery can also be printed at a very high resolution with other QGIS layers on a map and without it shifting relative to other layers; a conspicuous problem with OpenLayers that does not use “On the Fly” re-projection and only prints Google, Bing layers at a low resolution. It is an ideal aerial base map.

References:

QGIS: Adding An ArcServer Rest Service

Connecting to ArcGIS “mapserver” layers

Note: This method has been superseded by a plug-in that adds ESRI imagery and other REST layers via a GUI


Google Map Style with “Shape Burst” effect in QGIS 2.3

Here’s a nice looking map I created using QGIS 2.3, the testing version of QGIS. I downloaded free OpenStreetMap data and I styled it to look just like Google Maps, as per instructions published by Anita Graser. I also outlined county boundaries using the new “Shape Burst” effect, which creates a pleasing graduated colour pattern that faithfully follows polygon outlines (it’s also applied to the Sea, though it’s quite subtle). I used Data Defined Properties to restrict the effect to all counties except Dublin City, this also created a Mask.

Lastly, there’s also a subtle “Coastal Vignette” effect, these are fine lines that trace the coastline and were typical of old style hand drawn maps. Must have taken a tremendous amount of patience. I developed a simple method of reproducing the effect and I’ll let you know how I did it in my next blog post. Oh and by the way, the scale relates to a map printed at A3 size.

 


The 10th annual FOSS4G conference

The 10th annual FOSS4G conference was held from 8th-13th September in Portland, Oregon, USA. FOSS4G is the world’s premier global gathering of developers, users and key decision-makers involved in open source geospatial software. With over 180 talks presented covering topics from 3D printing maps with Grass GIS 7 to QGIS Map Server and beyond, FOSS4G 2014 was a resounding success. Don’t be disappointed if you could not attend, all the talks given at FOSS4G 2014 are now viewable on Vimeo, including 8 one hour invited presentations from staff at Amazon, MapZen, Boundless, Mapbox etc. These talks are well worth watching if you want to keep up to date with the latest developments in open source geospatial software.

FOSS4G 2014 General Sessions – Talks and Invited Presentations


Importing CSV files into PostgreSQL using the DB Manager in QGIS

There is very useful tool in QGIS that can import very large CSV files into PostgreSQL rapidly and reliably. The DB Manager’s “Import Vector Layer” tool. Contrary to its highly misleading title it can import CSV files as well. Open the DB Manager (menu Database – DB Manager). Then select the database where you want to store your table and click the “Import layer/file” icon.

Icon_to_ClickFrom the Import Vector Layer GUI, locate our CSV file on disk and enter the name of your new table in the Table box and click OK. Yes, it’s that simple. Proceeding this, you may need to select an text encoding scheme, files created on Windows often use ISO-8859-1 (Latin-1) instead of UTF-8 encoding. In my case, I was able to import a large statistical data set describing the energy efficiency of 525,500 Irish homes (432 megabytes) into PostgreSQL in ~15 minutes. After the CSV file is imported, you can optionally add it to your project using the DB Manager, right-click the table and select Add to Canvas. Don’t use the “Add PostGIS Layers” menu, it’s not a PostGIS layer.

Import_GuiAnd one more useful tip. You can convert Tab delimited text to CSV using QGIS. Load a Tab delimited text file into QGIS using the Add Delimited Text Layer GUI, then right click the imported file in the layer panel and save it as a CSV file.


Creating a Nautical Chart in QGIS 2.4

Continuing with a nautical theme, here is a nautical chart I creating using QGIS 2.4. It includes a Graticule in decimal degrees, a Compass Rose and a scale bar in Nautical Miles. A magnetic declination of 3º 35′ was determined using the MagneticField utility of GeographicLib, an advanced software library for solving geodesic problems. I will post a full tutorial shortly.

Nautical Chart for North Dublin Bay


Nautical Charts in QGIS – The Compass Rose

Before the advent of shipborne satellite navigation systems, navigation at sea required three precise measurements – Solar or Stellar Declination for Latitude, Time at Greenwich for Longitude and True North that determined the ship’s heading. True North was obtained from the ship’s Magnetic Compass, an instrument who’s name indicates at an additional complication.

A magnetic compass does not point towards True North. Magnetic North is 100s km from the Geographic North Pole and the Earth’s magnetic field is uneven, it is distorted by magnetic irregularities within the Outer Core and intrinsically magnetic Mantle and Crustal rock. Additionally, the position of Magnetic North is not fixed, it is presently drifting from Arctic Canada towards Russia at 15 km per year. Therefore True North has to be derived from Magnetic North using a correction called Magnetic Declination (or Magnetic Variation), the angular difference between Magnetic North and True North. Magnetic Declination varies from location to location and over time.

Nautical navigation charts typically contain one or more Compass Roses, also called a Windrose, these consist of two circles – an outer circle that displays the cardinal directions of North, East, South and West and a inner circle that displays the direction of Magnetic North. The Magnetic Declination and its annual rate of change is typically printed within the Compass Rose, it is therefore possible to calculate the Magnetic Declination several years after a map is printed.

In this tutorial I will show you a process that to create a Compass Rose with the correct Magnetic Declination and Annual Rate of Change for any terrestrial location for use in QGIS. First we need to obtain a suitable Compass Rose graphic. Conveniently the United States National Oceanic and Atmospheric Administration (NOAA) published a Compass Rose in the Public Domain i.e. it is free to use without limitation. I downloaded a version of the NOAA Compass Rose from Wikimedia (or you can right click and save the Compass Rose below). Additionally, the background of this Compass Rose is transparent, this allows a map (or indeed a web page) to show though (note the Magnetic Declination in 1985 was 4 degrees 15 minutes west of True North and it had an annual decrease of 8 minutes of a degree per year).

800px-Modern_nautical_compass_rose.svg

There are several handy on-line utilities that can calculate Magnetic Declination and the Annual Rate of Change but we shall use Charles F. F. Karney’s excellent cross-platform GeographicLib in this case. GeographicLib is a suite of command line utilities for solving solving various geodesic problems such as conversions between geographic, UTM, UPS, MGRS, geocentric and local cartesian coordinates, gravity calculations, determining geoid height, and magnetic field calculations. The latest version can be obtained as a pre-compiled binary from Sourceforge or as source code.

The other essential step is to measure the precise map location in WGS84 coordinates. This can be done using the Coordinated Capture plug-in provided as standard with QGIS. To select the WGS84 coordinate reference system (CRS) click the sphere symbol in Coordinated Capture panel to open the Coordinate Reference System Selector. After setting the CRS to WGS84 (EPSG: 4326), click the icon left of the “Copy to Clipboard” button (this toggles real time display of captured coordinates) and then click “Start Capture”. The position in Decimal Degrees will be updated in the upper window as you move the cursor across the map, the lower window will display projected coordinates (in my case Pseudo Mercator EPSG: 3857). Clicking the map will select a coordinate point and the real time display will cease updating.

Wordpress

The MagneticField utility of GeographicLib is then used to calculate the Magnetic Declination and Annual Rate of Change for the captured coordinate, in this case a location east of Howth, Ireland.

$ MagneticField -r -t 2014-08-04 --input-string "53.37772 6.00935"

-3.57 67.81 18572.9 18536.9 -1152.2 45528.7 49171.3
0.17 -0.01 17.9 21.2 52.4 19.6 24.9

The results are: Magnetic Declination in degrees (-3.57); the inclination of the Magnetic Field in degrees (67.81); the horizontal strength of the magnetic field in nanotesla (18572.9 nT); the north component of the field (18536.9 nT); the east component of the field in (-1152.2 nT); the vertical component of the field in nT (45528.7 nT) and the total field (49171.3 nT). The numbers on the second line are the annual rate of change of these values, the first number is. We only need the first numbers on each line; the Magnetic Declination (-3.57) and Annual Rate of Change of Magnetic Declination (0.17). We can convert these to Degrees Minutes Seconds if required.

After calculating the Magnetic Declination and Annual Rate of Change, edit the NOAA Compass Rose in a graphics program such as  GIMP or Photoshop. In my case I copied the inner circle to a separate layer and I rotated it 3.57 degrees anticlockwise. I then added text to the Compass Rose stating the Magnetic Declination (Var.) and the Annual Rate of Change (Annual Decrease). After editing the Compass Rose graphic I finally added it to my Nautical Chart as a Image in Map Composer of QGIS.

Further Reading:

Bowditch, N. & ‎National Imagery and Mapping Agency, 2002. CHAPTER 3. NAUTICAL CHARTS. In: The American Practical Navigator: An Epitome of Navigation. Bethesda, MD : Washington, DC, Paradise Cay Publications, 9, 23–50. ISBN: 978-0939837540 http://msi.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-03.pdf


Oceancolor Data Downloader v1.0 for QGIS

Aqua Modis SST 2015-01-13

Sea Surface Temperature data downloaded by Oceancolor Data Downloader.

The Oceancolor Data Downloader is a new plugin for QGIS from the Mapping and Geographic Information Centre of the British Antarctic Survey that downloads Oceancolor and Sea Surface Temperature data from NASA’s Oceancolor website. The plugin currently downloads three datasets:

  • MODIS AQUA chlorophyll concentration
  • SeaWiFS chlorophyll concentration
  • MODIS AQUA night time Sea Surface Temperatures

The data accessed includes daily, 8 day, monthly and yearly composites, all of which can be saved to disk while downloading. Future plans for the plugin include additional access to other datasets such as ocean Net Primary Production, selection by bounding box, the ability to save in other formats, a progress bar etc.

I used the plugin to download global Sea Surface Temperatures for the 13th Jan 2015. I then used shapefiles from Natural Earth to create a simple basemap. I finally chose the IBCAO Polar Stereographic projection (EPSG: 3996) to create a map centred on the North Pole.

If you use the plugin to produce published research, please cite:

10.5281/zenodo.15018


Go2streetview plugin for QGIS

A very handy plugin for QGIS I use day to day is go2streetview by Enrico Ferreguti. The plugin adds an icon to the tool bar in QGIS and when selected I can click a road or street on a base map and a window will open that displays the Google Street or a Bing Maps Bird’s Eye view of the location. The camera’s direction and location is highlighted by a blue marker. I use the plugin when tracing boundaries of parks, open spaces and foot paths from aerial imagery. If the imagery is blurred or the view is obscured by trees, I click a point on a nearby street to see the location up close. The plugin works wherever Google Street view and Bing Birds Eye has coverage.

For example, in the screen-shot below notice there is a footpath leading to a bus shelter that’s not mapped by OpenStreetMap. I know where it is now, I will add it to my map.

Street View

Plugin: go2streetview


CartoDB wins best “high-growth web entrepreneur” at the 2014 European Web Entrepreneur of the Year Awards

CartoDB, the FOSS powered web mapping solution, was honoured at the 2014 European Web Entrepreneur of the Year Awards along with three other companies at Dublin’s Web Summit on November 7th. The awards, presented by a European Commission backed body, were announced after a six month competition that involved public voting across four categories. CartoDB won the award for best “high-growth web entrepreneur”. CartoDB now has a growth rate of over 15% per month and customers in over 30 countries.

In September, a partner company of CartoDB, Kudos Ltda., released a plug-in that allows QGIS users to view, create, edit and delete data stored on their CartoDB accounts. Here is a map I created with the help of the new CartoDB plug-in that shows mountains and hills across the contiguous United States in the form of a heat map.

CartoDB and QGIS illustrate the exciting convergence between web hosted and desktop GIS, where interactive maps created in QGIS can be quickly published on the web and viewed by a worldwide audience.

FinalCartoDB


The Coastal Vignette

Vignette2

Coastal Vignette seen on an old Irish ‘6-Inch map’

Occasionally on old maps you may see a pleasing decorative effect on bodies of water called a “Coastal Vignette”, these are fine lines that highlight coastlines and lake shores. The example seen above is from a ca. 100 year old “6-inch map” of Lough Nafooey in County Galway, Ireland. I presume the Coastal Vignette effect in this example was hand drawn, it required considerable skill and patience.

These is no plugin for creating Coastal Vignettes in QGIS just yet, so I developed a simple technique to recreate the effect using the raster Proximity (Raster Distance)’ algorithm accessible in the Processing Toolbox.

In order to use the Proximity Analysis tool I first converted a Shapefile polygon depicting the sea off Dublin into a 10 by 10 metre resolution Raster using the menu command ‘Raster – Conversion – Rasterize (Vector to raster)’.

Box

This generated a Raster that coded the Sea as ‘1’ (white) and ‘0’ (black) for Land.

Next, I selected ‘Proximity (raster distance)’  from the Processing Toolbox – (GDAL/OGR) – [GDAL] Analysis – Proximity (raster distance). You can quickly find the command by typing the algorithm’s name in the box above the Processing Toolbox.

Screenshot5

I entered 0 in the ‘Values’ box, this tells the Proximity algorithm to measure the distance away from land (a value of 0). The resulting Raster contains cell values that correspond to the distance away from the coast in metres, which I styled below.

The final step is to create Contours Lines from the Proximity analysis result using the menu item Raster – Contour. In my case I used an “interval between the contour lines” of 200 metres and I added an Attribute name called “DIST”.

Screenshot7

The resulting contour lines have distance attributes attached to them can be used to create a Graduated colour style if needed, though in my cause I manually edited the attributes of 10 contour lines nearest the coast and I gradually increased the transparency of the mid-grey contour lines from opaque at the coast to fully transparent out at sea. I made the remaining contour lines transparent.

And here is the finished result, with the Sea and an OpenStreetMap base map styled to look just like Google Maps.

Finished Vignette 2


3rd Portugal QGIS user meeting (Covilhã) and QGIS‬ Conference 2015 (University of Copenhagen)

In the next weeks/months are due a couple of QGIS events where NaturalGIS will be present with presentations and workshops.

May 18th and 19th we will be at the QGIS Conference 2015 organized by the University of Copenhagen, Forestry College, that will take place in Nødebo, Denmark. This event is directly linked with the 13th QGIS Developer Meeting, that will take place from May 20 to 22 in the same location.

At the QGIS Conference we will make a presentation about how to get help/support for QGIS and a workshop about QGIS Server and how to publish OGC services (WMS/WFS/WCS) and webgis applications.

QGIS Conference 2015

June 5th we will be in Covilhã, Serra da Estrela, Portugal, to join the 3rd Portugal QGIS user meeting where we also will make a presentation (the same as in Nødebo) and a workshop about using the QGIS Processing toolbox.

3rd Portugal QGIS user meeting

Using Layer Visibility Presets in QGIS

One of the cool outcomes of our recent QGIS Legend Refactoring work was the ability to add "visibility presets". This feature allows users to save and load preset layer and group visibility settings.

Main canvas

First select the layers and groups, you’d like to manage visibility presets for. Now click at the top of the Layers panel and select Add preset … A new window will appear. Enter a name for the preset and click OK. Next time you click you should see the saved presets. The presets also save the visibility of categories in each layer.

In the video below, we create two presets. One for a specific site location and another zoomed to the outline of Great Britain which will be used as an overview in the print composer.

Print composer

The print composer now allows multiple map windows, each locked to a different layer visibility preset. This means a single map composer can show map windows with different layer arrangements.

In the video below, one preset is used for the main map and the other for an overview:

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