4

I have a shapefile of points with values that represent elevation at the given point. I know that I can create a TIN from these points, but the fields in the TIN do not represent the elevation. Rather, they represent an ID field for each node in the triangle.

I can also use the Interpolation plugin with Triangulated interpolation as the method. However, in this case it produces a DEM.

How can I produce a TIN where each node in the TIN represents the elevation at that point?

5

If you use is the Delaunay triangulation from:

  • Vector/Geometry Tool
  • or in Processing/Toolbox QGIS:Delaunay triangulation, SAGA:Triangulate or GRASS GIS/v.delaunay

All these algorithms perform a 2D Delaunay triangulation (only GRASS GIS allows a 3D Delaunay triangulation/interpolation but this command is not implemented in the Processing Toolbox)

enter image description here enter image description here

                   3D Delaunay with GRASS GIS

A solution is to:

1) First create a TIN with the Interpolation plugin (result = raster grid)

enter image description here

2) then use the Add grid values to points function from the Processing Toolbox

enter image description here

This function will extract the values from the raster layer and add them to the points.

  • The 3D Delaunay with GRASS 3D is what I am looking for, Gene. I tried it with the GRASS GUI 6.4.4 that comes with QGIS but it did not include the elevation as a field. I don't see any place to specify the elevation field. Can you describe how you created the two 3D graphs above? – Jim Jun 9 '15 at 17:21
  • With GRASS GIS (not QGIS) – gene Jun 9 '15 at 17:28
0

I have finally come up with a solution to the breakline problem. You need to take a few steps to get the required tin to be interpolated.

  1. Assuming you already have points with elevations in an elevation field (decimal) carry out a 'Delaunay triangulation' under 'QGIS geoalgorithms' of the GRASS toolbox in QGIS.
  2. Edit the delauny triangles using the node tool so that the triangles match your breaklines.
  3. Use the QGIS interpolation plugin and select the points layer as points and the Delaunay layer as either structure lines or breaklines.
  4. Run the interpolation plugin and it will use the Delaunay triangles as breaklines and create the surface you need.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.