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I am making a heightmap and am trying to interpolate a specific area on a point cloud in QGIS. I have found some ways of using GRASS to interpolate using the attribute table. The problem is that the attribute table is empty.

Is there any way to interpolate with GRASS by just using the z-coordinates, or maybe importing the z-coordinate to the attribute table?

  • Can you specify what format the original point cloud is? If you import into GRASS and there is no attribute table, then something is wrong :-). In general, GRASS can handle 3D layers and the interpolation modules can use the z value. – Micha Jun 8 '17 at 6:01
  • What interpolation module can use the z value? – Gisnoob123 Jun 8 '17 at 6:09
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I figured out that you can use the field calculator in the attributes table to make a new field, and in the expression window typing: z($geometry) to get the z-value into the attribute table.

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You can transform a 2D point shapefile into a 3D one with v.drape by adding in the processing the DEM from whom the heights are extracted. Then you can make a 3D interpolation with s.surf.rst (no need to define Z) or a multivariate one with s.vol.rst. The last one can interpolate you heights also by adding the Z values from the attribute table if you want to do an elevetation interpolation from a 2D vector with a Z value in the table. There is also oa plugin v.vol.idw for 3D IDW and v.kriging, which has also the 3D options, but it's quite complex and needs a good knowledge of spatial statistics.

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