AQGIS-Sivil3D

Corridor modelling on terrain for QGIS: typical cross sections, TIN, earthwork measurement, profiles and drawings.
Rafael Vázquez · Claude

1. What it is and what it is for

This plugin solves one concrete problem: extruding a typical cross section along an alignment, clipping it against the terrain and obtaining the resulting surface, with its measurements and its drawings. It is a Civil 3D deliberately reduced to that.

The complete workflow is:

1. You define one or more typical cross sections in the editor
2. You apply them to a line layer (a different section per run if you want)
3. The plugin clips them against any DEM and weaves the TIN
4. You get layers, earthwork volumes and, if you want, the merged terrain
5. You review the result in the profile viewer
6. You produce the drawings: plan, longitudinal, cross sections and earthworks
7. You save the whole corridor in a file to reopen it when needed

It works on QGIS 3.28 and later, including the 4.x series.

2. Installation and updating

Run instalar.bat from the project folder. It copies (or links) the plugin into the plugins folder of every QGIS profile it finds. Then, in QGIS: Plugins → Manage and install plugins → Installed, and tick AQGIS-Sivil3D.

Since version 1.0.0 the plugin is also in the official QGIS repository: Plugins → Manage and install plugins → All, search for «Sivil3D» and install it. There is no need to enable «Show also experimental plugins»: 1.0.0 was released as a stable version.

Merging with the terrain needs scipy, which ships with standard QGIS installations. Without it everything else works and the merge warns instead of failing.

2.1 Language: English or Spanish

Vector → AQGIS-Sivil3D → Language / Idioma…

The whole interface comes in English (the default) or Spanish. The choice belongs to the plugin and is not tied to the QGIS interface language, so you can keep QGIS in one language and the plugin in another.

The language reaches further than the menus. It also decides:

What is never translated is what gets stored: the keys of the section library, the field names of the output layers and the values written into them. That is what lets a project saved in one language be opened in the other. A corridor computed in Spanish keeps its Spanish layer names and point codes, and an English session still recognises them: it applies the right styles and the profile viewer still finds the axis.

3. The three concepts you have to understand

3.1 A typical cross section is a chain of rules, not a geometry

A section is not drawn: it is composed. Each element starts where the previous one ended and produces one or more vertices. That is what lets the same section adapt to a different terrain at every station.

Typical cross section
├─ axis        elevation (terrain | alignment Z), height difference, shift
├─ left  ────┬─ fixed[]   carriageway, shoulder, verge, kerb, ditch…
│            ├─ cut[]     applies if the terrain is ABOVE
│            └─ fill[]    applies if it is BELOW
└─ right ────┘            independent branch, same structure

The two branches are completely independent: a different slope on each side comes for free, with nothing to configure.

3.2 Each side decides on its own whether to excavate or fill

At every station and for each side separately, the plugin looks at the hinge point (the last element of fixed on that side) and compares the design elevation with the terrain one:

A section on a side hill comes out with one side in fill and the other in cut without touching anything.

6.2.0 Where the axis elevation comes from

The last two are typed in the field next to the drop-down. The height difference of the axis defined in the section editor is added in all four cases: with an offset of −0.30 in the dialog and a height difference of −0.20 in the section, the grade line ends up 0.50 m below the terrain.

6.2.1 Writing the elevation into the alignment Z

Next to the field there is a Write into the layer Z button, active with the two options that carry a value. With constant value it puts that elevation in the Z of every vertex; with offset from the terrain it drapes: each vertex takes the DEM elevation at its position plus the offset. In both cases it leaves the «from the alignment Z» option selected. From then on the grade line lives in the geometry and can be edited vertex by vertex with the normal QGIS tools: this is the way to start from a level platform and then give it grades.

There is one limit that cannot be worked around: the geometry type is fixed by the layer provider. Hence two behaviours:

With «selected features only» ticked, the elevation is written into those alone. The dialog warns before touching anything, and the log records how many features were modified.

When draping, if the DEM has no data at some vertex of an alignment, that alignment is left untouched and a warning is issued: better than giving it a made-up elevation.

The constant value is the shortcut for a level platform —a yard, the basin of a pond, a stockpile platform— and also for trying out how much earthwork a grade line would cost before having it designed: you set an elevation, compute and read the volume. The height difference of the axis is added in all cases, so with a constant elevation of 250 and a height difference of −0.5 the grade line ends up at 249.50.

3.3 The point codes are what stitch the TIN

Each element produces vertices with a code (CARRIAGEWAY, SLOPE_DAY…), to which the prefix L_ or R_ is added according to the side. The codes serve three purposes:

1. Stitching the TIN. Between two consecutive sections the mesh is woven by pairing vertices by code, not by index, using the longest common subsequence. That is why a section with 2 benches and the next one with 3 stitch together without twisting.
2. Naming the output feature lines (the breaklines).
3. Keeping continuity when going from cut to fill: using the same SLOPE code in both conditional groups is what you want, and that is why validation does not flag it as a duplicate.

The vertex where the slope cuts the terrain always carries the _DAY suffix, whichever element generated it, so that the daylight line is continuous. With several chained slopes the code is that of the last one even if it was the first that cut the terrain: this way the line stays a single one and the stitching keeps its anchor when the number of segments changes from one station to the next.

4. Typical cross section editor

Vector → AQGIS-Sivil3D → Typical cross section editor…

On the left, the library of sections. In the centre, the two branches with their three groups and the ordering buttons. On the right, the parameters of the selected element. Below, the section resolved over a test hillside.

4.1 The order is the geometry

Elements are resolved in the order they are in, so Up and Down change the result. The buttons are:

4.2 Preview

The test hillside is configurable and is the quick way to check that the slope daylights and that the bench fits, with no need for a DEM or an alignment:

Colours: brown the terrain, blue the design, ochre the cut, green the fill. A green circle is a daylight point; a red circle, a truncated slope that never reached the terrain.

4.3 Section library

The library is a JSON file that lives in the user profile (<QGIS profile>/aqgis_sivil3d/secciones_en.json), so it is not lost when the plugin is updated. It can be imported and exported to share it.

There is one library per language: secciones_en.json and secciones_es.json. They are not shared because the name of a section is its key —it is what you write in the alignment field to choose which section applies to each run— and the point codes travel to the output layer attributes. Each language therefore starts with its own catalogue, in its own language, and the first time you use a language the plugin writes it for you.

4.4 The nine sections in the pack

All nine are already in the library the first time you open it. The complete pack also travels inside the plugin, in docs/secciones_pack.json, in case it needs reimporting.

4.5 How a dam is computed

The body of a dam is raised from the terrain up to the crest, so it goes entirely in the fill group: the slope starts at the crest edge and goes down until it meets the valley. The cut group only comes in where the terrain is above the crest, that is, at the abutments.

Two things are done differently from a road:

1. The axis elevation has to be a constant value (see 6.2.0): the crest is level. With the DEM option you would get a body that rises and falls following the terrain, which is not a dam.
2. The alignment is drawn along the crest, from abutment to abutment.

And for the basin, the reservoir capacity curve tool (see 13) gives the elevation-volume-area relationship from the DEM.

4.6 Validation warnings

The strip at the bottom warns about the problems that can be detected without terrain:

5. Element catalogue

The last two seek the terrain, and the last element of a conditional group has to be one of them for the surface to close. With talud_banqueta, the number of benches is decided by the terrain at each station, not by you.

5.1 A slope with two or more gradients

An intermediate talud_daylight is also valid, and that is how a slope that changes gradient is defined: 1:1 up to 2 m of height and 1:1.5 from there on, for example. You put two slopes in a row and give the first a segment limit of 2 m:

• If the terrain appears within those 2 m, the first slope closes there and the second never acts.
• If it does not, the first ends in a break when it reaches the limit and the second carries on seeking the terrain from that point with its own gradient.

The break is a normal vertex: it anchors the TIN stitching and comes out as a feature line (the change-of-slope line), but it is not part of the daylight line. It appears only at the stations where that segment did not reach the terrain, just like the benches.

Its code is numbered automatically: SLOPE_Q1, SLOPE_Q2… That is why the slopes of a chain can all be called the same, and in fact that is what you want: they share the code of the daylight vertex, so the toe or crest line comes out in one piece, and their breaks do not get confused with each other because they are numbered. Validation does not flag a repeated code between chained slopes of the same group as a duplicate.

5.2 Benches, catch ditches and anything else in between

Behind a slope there can be any element, not just another slope: a bench (Offset with slope with a slope of 0 or a slight adverse slope), a catch ditch, a vertical segment… and then another slope. They alternate as many times as needed, and the last one in the chain is the one with no segment limit, so that it closes.

This is how a tall embankment is defined giving each segment its own slope, its own height and its own bench, which is what a real case usually asks for. The Benched slope element always repeats the same [slope + bench] pair; by hand you get control segment by segment, at the price of writing several elements.

In front of the first slope this does not happen: there the elements are a continuation of the platform and are always drawn. That is what lets the ditch of the road and track templates —which is the first element of the cut group— keep working the same way, and stops a shallow cut from closing at the ditch without reaching the slope.

The limit is measured by elevation (vertical height of the segment) or horizontally (distance covered), as you choose. More than two slopes can be chained; the last one is the one with no limit. Two details:

• The field is only active if there is another element behind to hand over to. On the last slope it appears disabled.
• The maximum height is a different thing: it is a hard stop and, if it is reached without meeting the terrain, the section is left open and a warning is issued. If you set it below the segment limit, the hand-over would never happen and validation tells you.

5.3 How values are written

5.4 Dynamic parameters

Any parameter also accepts two forms that are resolved once per feature of the alignment:

In the editor, the test values box lets you preview a section with dynamic parameters: width=7, cut_slope=1:1. Anything not given uses the parameter's default.

6. Computing the corridor

Vector → AQGIS-Sivil3D → Extrude typical cross section (corridor)…

6.1 Inputs

6.2 Options

6.3 Details that affect the result

DEM sampling. It is interpolated bilinearly between the centres of the four neighbouring pixels, the pixel value is not taken. With pixel values, the search for the cut jumps and the daylight line comes out saw-toothed. Reading goes through cached tiles, because each bisection is about 40 samples.

Tight curves. On the inside of a curve the normals converge and beyond a certain distance from the axis the adjacent sections cross. The plugin computes that distance per station and warns if the section width exceeds it: reduce the station interval or smooth the alignment. It does not fix it on its own.

NoData. If the axis falls on NoData, the section is discarded. If it is the slope that enters NoData, a warning is issued and it is truncated.

7. Merging with the base terrain

With the option on, the output TIN also includes the original terrain around the corridor, stitched to the daylight line, so that a single continuous surface is obtained.

How it works: the terrain is sampled on a grid, the nodes that fall inside the corridor footprint are discarded (and those too close to the edge, which would only give sliver triangles), the densified footprint with the corridor elevations is added —those are the seam nodes— and it is triangulated. Then the triangles whose centroid falls inside the footprint are thrown away.

If the requested cell would give an unmanageable grid, it is enlarged and a warning is issued, instead of exhausting the memory. The result has no gaps or overlaps: in the tests, the sum of the triangle areas matches the complete rectangle.

8. Output layers

They all come out inside a group called <alignment>-corridor, ordered for drawing and with symbology applied. Each computation creates a new group (… (2), (3)…) so that alternatives can be compared.

8.1 Cut and fill colours

The TIN comes out categorised by the zona field:

The classification is done triangle by triangle comparing its mean elevation with the terrain one under its centroid. The espesor field stores the signed height difference (negative excavates, positive fills), so the colour can also be graduated by earthwork thickness. They are the same colours as the editor preview.

9. Earthwork measurement

The cut and fill areas of each section are obtained by integrating between the design line and the terrain one, splitting at the crossings: it is not an estimate, it is the exact area of the polygons you see shaded.

The volumes go by average end areas:

V = (A1 + A2) / 2 · L

which is the design convention and the one to use if the numbers have to match a measurement done by hand. There is also the prismoidal method, which damps the bias at the change from cut to fill, where one of the two areas is zero.

The mass haul diagram is the cumulative net volume, with a configurable bulking factor: 1.0 means that one cubic metre excavated fills one cubic metre; 0.9, that only 90 % is usable.

The measurement comes out in two places: the cross sections layer carries cota_roja, area_des and area_ter per station, and the earthworks table carries, for each run between consecutive sections, the areas, the cut and fill volumes, the net and the cumulative.

10. Profile viewer

Vector → AQGIS-Sivil3D → Corridor profiles

Dockable panel with three views of the computed corridor:

10.1 Controls

Navigation is synchronised with the map both ways: as you move through the stations the section is highlighted on the map with a rubber band, and clicking on the map (with the box ticked) jumps to the nearest station. You can also click directly on the longitudinal profile to go to that station.

10.2 Seeing several alignments at once

The Alignments box is the same widget in the viewer and in the drawings dialog. It lists one row per alignment (one per feature of the alignment layer) of each corridor in the session, with its own colour and a checkbox:

The All / None / This one only buttons are shortcuts. Highlighting a row of the list also makes it the main one, and the other way round. The main one need not be checked: you can compare two alignments on the longitudinal while looking at the section of a third.

The Order drop-down sorts the list by creation date (oldest corridors first, which is the order in which they were computed) or by name, alphabetically. With many alternatives in the session, alphabetical is the one that lets you find one by its name. Reordering changes nothing else: the colour of each alignment does not depend on its position in the list, so one that is drawn does not change colour when reordering, nor is anything you had ticked lost.

In the drawings the criterion is the same, but each drawing does what makes sense with several alignments:

It is decided by the Drawing set drop-down, which is at the top of the dialog because it rules over the three drawings (see 11.3):

And in all three, with the Others box ticked, the other corridors are drawn where they cross or run close. See 11.4.

11. Automatic drawings

Vector → AQGIS-Sivil3D → Generate drawings…

11.1 How they are made (and why this way)

QGIS has no layout item that draws profiles, and assembling hundreds of layout polylines is not viable. So «drawing on the sheet» is turned into «generating geometry»: a paper-space drawing layer where X and Y are millimetres of paper and each section is translated to its cell of a grid. The drawing is nothing more than a map framed on that layer.

Advantages: it is symbolised with QGIS like any other layer, the atlas paginates on its own, DXF export comes for free and the scales stay explicit.

11.2 The four drawings

11.3 With several alignments: which drawing set comes out

A drawing is that of one axis: its cross sections are the cuts of its route and its longitudinal is its vertical plane. With several alignments checked you have to say whether you want a single project or several, and that is what the Drawing set drop-down is about, at the top of the dialog next to the list of alignments:

11.4 The other corridors in the drawing

With the Others box ticked (it is on by default), the drawing of one alignment also shows the rest:

The other traces are drawn dashed and in purple, so that they are not confused with the design being dimensioned, and they are clipped to the frame of the cell: a corridor passing 40 m away from a drawing that spans 15 cannot end up painted over the title block. If it does not fit, it is not shown.

The cut is made against the two families of lines of the other surface: the longitudinal ones (the feature lines) and its own sections. Both are needed: with nearly parallel alignments the plane crosses the longitudinal ones, and with two that meet at a right angle the opposite happens —the other's longitudinal lines are parallel to the plane and never touch it—.

11.5 Which layers appear in the plan

The Drawing layers box lists the project layers that can go to the map and lets you tick the ones you really want. By default the corridor outputs (TIN, footprint, axis, feature lines, cross sections, stations) and the alignment are ticked; the rest of the project —cadastre, orthophotos, working layers— is left out.

The buttons are All, None and Corridor only. Paper-space drawing layers are not even listed: their coordinates are millimetres and on the map they would appear hundreds of kilometres away.

11.6 Why a longitudinal sheet does not fill the paper

The longitudinal profile sheets are cut for two reasons: because the paper width runs out or because the height no longer fits. The second one is what throws you: you choose A3 and get strips that take up half of it.

With A3 landscape and margins, about 366 mm of usable width and 221 mm of drawing height are left. At a horizontal scale of 1:1000, 366 m of axis fit per sheet; at a vertical scale of 1:100, 22 m of height fit. If the terrain rises more than 22 m in less than 366 m —a grade above 6 %—, the height rules and the sheet is cut earlier:

It is not a fault: if the drawing does not fit vertically, it has to be split. The fix is to lower the vertical scale (1:200, 1:250) or raise the horizontal one. The log says so when generating, with the scale that would fill the sheet.

11.7 Dialog options

12. Vertical alignment editor

Vector → AQGIS-Sivil3D → Vertical alignment editor

It is the longitudinal profile in digitizing mode: the grade line is drawn with the mouse over the terrain, with the same tools used to digitize in plan view, and when finished it is written into the alignment Z. From there the corridor is computed with axis elevation = alignment Z (see 6.2.0), so this editor is the missing piece for designing in elevation without leaving QGIS.

12.1 Getting started

The view is handled like any other drawing: wheel to zoom around the cursor and middle button dragging to pan.

12.2 How it is handled: two modes and a few actions

The first thing to be clear about is that the bar has two different things:

The actions can be used in two ways: with a segment already selected (they apply when you press the button, and that is it) or with nothing selected (they stay armed and apply to the segment clicked next). Below the bar there is a label that says at each moment what is expected of you.

12.3 What can be dragged

When you hover over it, what can be grabbed is surrounded by a circle, and the segment under the cursor is marked in bold. If nothing is highlighted, there is nothing to grab there.

12.4 Several vertices at once

The grade line is an elevation law independent of the plan: its vertices have nothing to do with those of the alignment polyline. Even so it can have quite a few, and raising or lowering a whole stretch one by one would distort the grades along the way. That is why several can be grabbed:

The group's vertices are painted orange, and the top left shows how many are grabbed.

12.5 Simplify: the grade line does not inherit the plan vertices

An alignment can have hundreds of vertices, and if the grade line is already written in its Z it will be densified as well. Reading that vertex by vertex would give a grade line of three hundred nodes that nobody can handle.

That is why, when reading the layer Z, it is simplified with the tol. field at the bottom (tolerance in metres of elevation): it keeps the vertices that really define the grade line, guaranteeing that at no point does it depart more than that tolerance from the original. With 0 they are all read. The Simplify… button does the same on the grade line being edited.

12.6 Shortcuts

12.7 The short route

1. Choose the alignment and the DEM: the terrain profile appears.
2. From the terrain with 4 or 5 vertices: you already have a starting grade line.
3. Drag the squares until you like the grade line, watching the cut and fill shading.
4. If some stretch asks for a curve: click the segment (it gets highlighted), press Arc, Bézier or NURBS, and drag the circles.
5. If it is a road grade line, better leave it straight and put vertical curves with their K at the vertices (12.8): that is how it is designed and how it is checked.
6. Finish off the numbers in the table and press Apply to the layer Z.

12.8 Vertical curves (L and K)

Besides the segment types —which are those of plan digitizing— each inner vertex accepts a vertical curve: the good old symmetric parabola that rounds the corner between two straights. It is the tool actually used when designing a road and it has no equivalent in plan.

It is defined in two ways: by writing its length L in the corresponding column of the table, or by writing its K and pressing Apply K. K is the metres of curve per 1 % of grade change, which is how it comes in the standards; the editor computes L = K · |Δ grade in %| and the other way round.

In the view, the vertical curve is labelled with its L and its K, and its two ends are marked with a small circle: that is where the curve begins and ends.

12.9 Drawing settings

The table on the right is the other half of the editor: station, elevation and L are typed in, and the segment type, the K and the grade are read. It is how a grade line is finished off when it is nearly there: with the mouse you look for the shape and with the numbers you close it.

12.10 What is shown in plan

While editing, the map highlights the alignment of the run with a rubber band and marks with a cross the point the mouse is over and the selected vertex. The readout at the top of the view gives, for the cursor position, station, elevation, terrain elevation and cut/fill depth. Cut and fill are shaded in the same colours as the rest of the plugin (ochre and green), so you can see at a glance which part of the grade line excavates and which part fills.

12.11 Apply to the layer Z

Apply to the layer Z writes the grade line into the geometry of the run being edited:

• if the layer accepts Z (LineStringZ), it is edited in place, within a normal editing session;
• if the layer is 2D, there is no way to give it Z —its provider prevents it—, so a new layer is created with the same fields and attributes and the Z set.

The step field is the densification: besides the vertices the alignment already has, points are inserted at that step and at the singular points of the grade line (vertices and ends of each vertical curve). It is needed because a parabola between two vertices 300 m apart would be lost if only its ends were written. With a step of 0 only the existing vertices are written.

12.12 Limits

• A grade line is a function of the abscissa: each station corresponds to one elevation and only one. A Bézier or a NURBS with the handles pulled far out can fold back on itself; in that case the increasing-abscissa envelope is drawn and applied, and a warning is issued.
• The vertical curve is a symmetric parabola. There are no asymmetric curves or circular curves in elevation.
• The grade line is stored in the layer Z, not as an object of its own in the project: that is what makes it usable by the rest of the plugin and by any other QGIS tool, but it also means that the segment types and the vertical curves do not travel with it. What travels is the densified geometry.

13. Reservoir capacity curve (elevation-volume)

Vector → AQGIS-Sivil3D → Reservoir capacity curve

Characteristic curve of a reservoir or pond from the DEM of its basin: for each elevation, the stored volume and the flooded area.

13.1 What is computed

For a water level e:

• area = number of cells whose bottom is below e, times the cell area;
• volume = sum of (e − bottom elevation) over those cells, times the cell area.

It is the usual computation, but solved by histogram accumulation: each cell is classified once according to the elevation from which it starts counting, and two cumulative sums give the complete curve. The result is exact and the cost does not depend on the number of elevations, so a basin of several GB with a 10 cm step comes out in a single pass. The DEM is read in blocks, through GDAL when it is a file and through the QGIS provider when it is not.

13.2 Inputs

13.3 Outputs

With the folder given and the box ticked, the CSV and the PNG are written when the computation finishes; the Save CSV and Save PNG buttons let you choose the place by hand. The clip files carry the -basin suffix so as not to overwrite those of the complete DEM.

13.4 The water surface style

The clipped DEM is loaded with a blue ramp in interpolated pseudocolor: dark blue at the bottom and light blue, increasingly transparent, towards the shore, so that where the depth is small the terrain underneath shows through. The ramp is stretched between the minimum and maximum elevation of the clip, so the same style works for a pond 3 m deep and for a reservoir 60 m deep with nothing to change. The value 0 is left transparent, because in a clip it is a hole and not an elevation.

13.5 Reading the curve

Moving the mouse over the chart reads the elevation, volume and area of each point; clicking pins an elevation, which stays drawn with its label. The two panels share the elevation axis and have their own scale: they are two different magnitudes, hm³ and ha, and a double Y axis would force you to look at two scales to read a single point.

13.6 Things worth knowing

• The cell area comes from the raster resolution, so the DEM has to be in a projected system (metres). In degrees, the result means nothing.
• The NoData declared in the raster is respected. If the basin comes with the hole at −9999 and undeclared, it has to be declared first or clipped away.
• The curve is computed on the cells as they are: the water surface is not interpolated within the cell, which is what gives the volume the error inherent to the resolution (with a 2 m cell, of the order of tenths of a per cent).
• The computation is limited to 200,000 elevations: an absurd step is rejected before starting.

14. Saving and recovering a corridor

Corridor file → Export corridor to file… and Import corridor from file… (a single toolbar button with a drop-down; in the menu they are two separate entries)

The output layers are in memory: they are lost when QGIS closes. Exporting writes two sibling files:

The JSON is what the GeoPackage cannot store and without which nothing but the drawing is recovered. With it, on import the whole corridor comes back and you can use the profile viewer, measure and generate drawings without the DEM and without recomputing.

To export, select the corridor group in the layers panel. If you only want the drawing, the .gpkg on its own will do; importing it without the JSON warns that the viewer will have no data.

15. Several corridors at once

Each computation and each import is registered as an independent alternative, with the group name (axis-corridor, axis-corridor (2)…). They do not overwrite each other, so they can be compared.

The Alignments box of the profile panel and of the drawings dialog lists the alignments of all the alternatives together, so there is no need to pick one and discard the rest: you tick the ones you want to compare, whether from the same corridor or from different ones. See 10.2.

15.1 Corridors survive closing QGIS

A computed corridor is more than its layers: the resolved sections —what the profile viewer and the drawing generator need— live in memory and are not in any layer. So that they are not lost on closing, the plugin saves and recovers them on its own by two routes:

Recovery is attempted on opening the project and also on opening the viewer or the drawings dialog, in case you have just loaded a GeoPackage by hand. What was computed in the working session always takes precedence over what was recovered, which is older.

Only what is still loaded in the layers panel is recovered. Either of the two tests will do: that its layer group is there —which is the normal case when reopening a project, because the alignments may not have been saved in it— or that its alignment layer is there, which is the test when it has just been computed and no group has been loaded yet. If neither remains, nothing of the corridor is left in the project and it is not offered: deleting a corridor's layer group is the way to remove it from the viewer and the drawings. They used to be offered anyway, and old alignments appeared that led nowhere.

16. From Processing

The aqgis:corredor algorithm is in the Toolbox, provider AQGIS-Sivil3D, group Corridor. It is meant for models, batch processes and the console:

import processing
processing.run("aqgis:corredor", {
    "DIRECTRICES": line_layer,
    "DEM": dem_layer,
    "LIBRERIA": r"C:\...\secciones_en.json",
    "CAMPO_SECCION": "section",
    "SECCION_DEFECTO": "Road 1+1",
    "PASO_PK": 10.0,
    "INCLUIR_VERTICES": True,
    "COTA_EJE": 0,            # 0 = from the DEM, 1 = from the alignment Z
    "INTERVALO_PK": 100.0,
    "FUSIONAR": True,
    "CELDA_FUSION": 0.0,      # 0 = DEM resolution
    "HOLGURA": 50.0,
    "GRUPO": "",              # empty = <alignment>-corridor
    "OUT_TIN": "TEMPORARY_OUTPUT",
    "OUT_SECCIONES": "TEMPORARY_OUTPUT",
    "OUT_LINEAS": "TEMPORARY_OUTPUT",
    "OUT_HUELLA": "TEMPORARY_OUTPUT",
    "OUT_EJE": "TEMPORARY_OUTPUT",
    "OUT_PK": "TEMPORARY_OUTPUT",
    "OUT_2DM": r"C:\...\corridor.2dm",
})

The fine parameters (sampling step, maximum half-width, start station, DEM band, elevation factor and offset, merge extent, library as JSON and layer group) are under Advanced.

17. Warnings and common problems

18. What this plugin does not do

• It does not design the grade line for you: it uses the terrain or the Z you give it.
• It does not resolve transitions between different sections from one run to the next.
• It does not do automatic superelevation (it can be imitated with @field parameters or expressions).
• It does not fix section crossing on tight curves: it only warns.
• It does not model structures (bridges, retaining walls with foundations…).

19. For whoever maintains the code

The separation is deliberate: core/ is pure Python and imports nothing from QGIS, so all the delicate geometry (the TIN stitching, the daylight search, the measurements, the paper space) can be tested without opening QGIS. gis/ is what talks to QGIS; ui/, the interface; processing/, the algorithm; i18n/, the language catalogue.

python -m unittest aqgis_sivil3d.tests.test_core \
                   aqgis_sivil3d.tests.test_medicion \
                   aqgis_sivil3d.tests.test_paperspace \
                   aqgis_sivil3d.tests.test_i18n

Those of the QGIS layer need the QGIS Python: aqgis_sivil3d.tests.test_gis. Among them there are two guards worth not removing: one checks that no PyQt5 APIs removed in PyQt6 are left (exec_, QRegExp…), and another that there are no unscoped Qt enums outside ui/qtcompat.py. They are faults that do not show on import, only when you press the button.

On texts: the literal in the code goes in English, which is the original language, and it is translated with t(). What is stored —internal keys, field names, the section library format— is never translated. test_i18n checks that the format placeholders of the Spanish catalogue match those of the original, because a mismatched one would leave the string unformatted on screen.

20. Authorship and licence

Written by Rafael Vázquez with Claude (Anthropic). Version 1.4.1.

It is distributed as free software under the GNU General Public Licence, version 3 or later (GPL v3+). Anyone can use it, study it, modify it and redistribute it, but with one condition that makes it the most restrictive of the free licences: whoever distributes the plugin, or a modified version of it, has to do so under this same licence and hand over the source code. Nobody can close it or integrate it into a proprietary product. It is delivered without warranty of any kind.

The full text is in the LICENSE file that accompanies the plugin, and also at gnu.org/licenses.