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I have a shapefile containing buildings represented as polygons (basically the area of the buildings).

In the attribute table there is a field where the elevation of every building is stored (every building/polygon as a different elevation). Elevations are stored as decimal numbers.

What I am trying to do, is to convert this 2D shapefile in a 3D shapefile using the elevations stored in the "z" field of the shapefile.

With ArcGis it is possible with the tool Feature to 3D by attribute

I cannot find anything similar in QGIS.

I tried "save as" and then include "z dimension" but it does not prompt to choose a field where elevations are stored.

I also tried the v.extrude Grass command, but none of the field in the attribute table are shown to select from as height field.

Is it possible with QGIS/Grass to do this?

My final goal is to obtain buildings as 3D objects.

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I guess if you have None as a value for the v.extrude command, it's because your data is not in the right format (string instead of real for example). See below, it works for me :

v.extrude

In case you need, GRASS has a v.to.3d command that transforms 2d vectors to 3d vectors. It'll pass Point into PointZ or Polygon to PolygonZ.

v.to.3d - Performs transformation of 2D vector features to 3D.

See https://grass.osgeo.org/grass72/manuals/v.to.3d.html

v.to.3d

  • Just checked, my elevation data are stored in a field type "double", type name "real", precision "2", lenght "10". – Vale Sep 8 '17 at 8:15
  • Ok, I managed to make it work using GRASS inside of QGIS, and not in the GRASS GUI. The extrusion of some of the buildings failed, but in the GRASS GUI I can see the others as 3D. I don't know why the SAME exact command worked inside QGIS and not inside the GRASS GUI. Now I will have to adjust the buildings that where not extruded and find a way to export them to be used outside of GRASS. – Vale Sep 8 '17 at 8:22
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    @Vale I think i already ran into this type of strange behavior, where the software didn't recognize double field type, but it did recognize real field type. – gisnside Sep 8 '17 at 18:46
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    Hi all, I'm totally new here and totally new to the world of GIS. I've had a similar problem but I wanted the footprints to be at the correct elevation and for the extrusions to have correct heights. Fortunately my input shape file had the right data. I ended up doing this in two passes. First I used the VectorGeometry.Translate process to move the footprints to their correct elevations. Then I used the v.extrude process on the resulting translated layer to extrude the footprints. It worked perfectly. All this in QGIS 3.2.2-Bonn – Tomek Sep 14 '18 at 1:15
  • Further to my previous comment, after exporting to DXF format in order to import into my architectural application, it turns out that the extruded footprints appear as wireframes. I was hoping to get boxes with filled sides, if that makes sense. Anyone know how to do that? – Tomek Sep 15 '18 at 10:20

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