Grid Generating with BASEmesh - Problems with Elevation meshing

JonasStuder · 2019-03-11 18:05:11

Dear Basement community,

I just started using Basement and finished the Tutorials. Now I’m trying to run a model with my own data, but I have some problems generating the elevation mesh:

I have a question concerning grid generation (for 2D) based on elevation points (DEM). According to the manual, all corner vertices of the model boundary must lie on elevation points for creating an elevation mesh. In my example this is the case. There are 37 points with XYZ values exact on the same location as the 37 vertices from the model boundary (as shown in figure 1). Further there are a lot of XYZ points within the model boundary (as shown in figure 2). There are no breaklines used in this model. When I’m using the BASEmesh elevation meshing function, the output only generates cells with the nodes from the model boundary (as shown in figure 3) an not with the other XYZ points whitin the boundary. Further the Z values of the new generated nodes are all 0 (as shown in figure 4).

I checked, that the vertices of the boundary are at the same location as the corresponding XYZ points.

I don’t know how to solve this problem and would be happy for some advice.

Thanks
Jonas

Last edited by JonasStuder (2019-03-12 11:21:07)

Stephan Kammerer · 2019-03-12 10:42:37

We cannot see your figures!

Have a look at the help on how to insert links and images.

Did you use snapping in QGIS (Settings -> Snapping options) to place the vertices of your domain boundary?

JonasStuder · 2019-03-12 11:25:49

Thanks for your answer. I edited the post.

Regarding your question: I generated the boundary with the QGIS function "convex hull" further I snapped one point to check if this would help. But it is still the output shown in the figures.

Does someone know a solution?

BR, Jonas

Last edited by JonasStuder (2019-03-12 13:36:06)

Stephan Kammerer · 2019-03-13 10:01:10

This seems to be a problem of the raw data handling. Did you define the correct coordinate reference system before loading the point DEM?
Another option would be to change the Relative snapping tolerance in BASEmesh.
Different data sources (shape-files, ascii-files, Triangle output, manually added features) might have different floating point precisions. The Relative snapping tolerance defines how far two point coordinates may be located apart to still be considered at the same location. The default value is 10E-6. From my experience changing to 10E-04 can help to solve snapping issues!

JonasStuder · 2019-03-14 10:16:20

Thanks for your input.

I checked all the coordinate reference systems and used snapping tolerance. But it didn’t work.

I think there was another problem. My DEM input file is a PointZ type Shapefile with defined Z coordinates. It appears, that QGIS has problems working with such files. When I clipped the DEM points in QGIS to my model boundary, somehow the Z geometry values were set to “0”. I noticed this by using the “z( $geometry)” command in the field calculator tool. It seems, that the “BASEmesh – Elevation meshing – tool” took this “0” Values in the Z geometry of the DEM input instead of the chosen elevation field “Z” in the attribute table.

Finally I was able to generate the Mesh by using the DEM with the correct “Z geometry” values (by using Clip in ARCGIS). It would be interesting to know, if others had similar problems with PointZ Shapefiles?

Thanks and BR Jonas

User Forum of Software BASEMENT

#1 2019-03-11 18:05:11

Grid Generating with BASEmesh - Problems with Elevation meshing

#2 2019-03-12 10:42:37

Re: Grid Generating with BASEmesh - Problems with Elevation meshing

#3 2019-03-12 11:25:49

Re: Grid Generating with BASEmesh - Problems with Elevation meshing

#4 2019-03-13 10:01:10

Re: Grid Generating with BASEmesh - Problems with Elevation meshing

#5 2019-03-14 10:16:20

Re: Grid Generating with BASEmesh - Problems with Elevation meshing

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