Bed Elevation group always added for .ply file

[jmkerloch]

There is always a group Bed Elevation added in the PLY Driver :

MDAL/mdal/frmts/mdal_ply.cpp

Line 305 in deba23b

MDAL::addBedElevationDatasetGroup( mesh.get(), mesh->vertices() );

I'm doing some tests with MDAL supported files and it seems that it's added for many drivers.

Is there any reason for that ?

[PeterPetrik]

Historically MDAL is/was used for hydro-data where bed elevation is almost always good to have. I am not sure now, but QGIS may have some special treatment of bed elevation dataset for displays.

[runette]

When the PLY driver reads a file - it uses the Z dimension to create a bed elevation data set. It does this - mainly because that is how the other drivers (particularly the TIN driver which was the template for the PLY driver) already worked! I think this is probably a historic artifact but MDAL does seem to assume that a bed elevation dataset exists - possibly because some of the early hydro data formats are set up that way. It is kind of counter intuitive and it would probably be better not to always have it and to have more conventional X,Y, Z geometry only for the mesh but I am not sure how much work that would be.

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