[Qgis-user] TIN Interpolation Error

[Maria Alicandro]

HI everyone,
I have a dataset of contour lines and elevation points and I want to create
a TIN model from these dataset.
In a first moment the software crashed. So I checked the geometry of the
shapefile with the "Geometry check" and some lines were duplicate. After
eliminating the duplicate geometries, the interpolation starts but it stops
at 22%. I changed the computer machine and I tried also a old qgis version
2.18 and I had the same problem.

I made other tests:
I noted that the shapefiles contain the z and m values (POINTZM and LineZM)
I saved the dataset (export - save features as) without the z-coordinates
(see Figure) and the tin interpolation crashed again.
[image: image.png]

Finally I remove the z and m values with the tool "Drop Z/M Value" in the
processing tools.
In this way the interpolator works.

I don't understand because if I remove the z and m values with the "Drop
Z/M values" tools, the interpolator works and if I eliminate the value from
the export the interpolaor doesn't work. (Is not the same thing?)

Moreover, is it possible that the problem is the z and m values? I think
that the z-values is stored specifically for the interpolation tools or am
I wrong?
Finally, I want know if is this the right strategies or there are other
problems in the dataset, which are somehow resolved by the "Drop Z/M valus"
tools?

Does anyone have any ideas or had the same problems?

Thanks, in advance for any tips

Maria
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