We use point heights from a survey to generate a TIN. In order to improve the quality of the TIN, additional break lines should be defined.

These break lines shall receive the height information from the point heights, where intermediate values of the vertices shall be interpolated.

How can these steps be achieved with QGIS:

  1. Taking the height from the points at the start or end point of a line
  2. Interpolation of the height for the vertices in between

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If you want to stay within QGIS, you could try the TIN Interpolation tool to interpolate a raster surface using your input points (Z from attribute or geometry) and lines as breaklines and specifying an appropriate pixel size. You could then use the Drape tool to assign Z values to your lines based on the interpolated surface raster generated in the previous step.

Please refer to the following posts regarding PostGIS methods for creating PolyLineZ geometries from 2d lines and points with z values:

PostGIS -> LineString + PointZ = LineStringZ

Assign Z value to start & end of PostGIS line

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