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I can't seem to get Breaklines to behave as defined here with the QGIS 3 (3.10 today) built-in Interpolation (TIN or IDW) . In my case I am preparing a subsurface structure map with geologic faults (Breaklines) with vertical displacements. Contours should end at opposite sides of each fault reflecting the displacements.

I have seen one answer where the user moved TIN triangle vertices to end at Breaklines to control interpolation. This would be a tedious manual task for many subsurface maps. I am not a very proficient programmer so I am trying to use the built-in capabilities of QGIS. Most of the previous questions on Breaklines were submitted while the Interpolation Plugin was in use (prior to QGIS 3).

Is there some documentation how to prepare the Breakline Layer?

Are my expectations not consistent with QGIS developers' intentions?

I put together a simple map as a test. The following images are from that test. The GUI shows my selections for the interpolation. I tried the Use Z-coord selected as well. Interpolation GUI. I have tried with Use Z-coord selected and not selected. Fault Layer Attribute Table

Fault Layer Attribute Table

Resulting Map with contours. enter image description here

Joel
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1 Answers1

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I believe I have answered my own question. The fault had a CRS different than the Project and the Points Layer. Both were XY units and appeared on the map correctly. Reprojecting the fault to the same CRS as the Points Layer and the Project resulted in the expected behavior.

A new map with the Breakline functioning is inserted below. The map is a little ugly and I have changed some of the data points, but you can see that the Breakline imparts the discontinuity on map. New map with Breakline working

It would be useful to be able to apply Breaklines so that the line was a boundary to triangulation and the structure on each side of the Breakline was extrapolated to the Breakline.

Joel
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