User Forum of Software BASEMENT

Marulke

User

Registered: 2015-11-14

Posts: 24

Tutorial 1, the hole boundary does not work properly?

I have gone through the BASEmesh tutorial 1 for QGIS, and I can not make it work as described.

In the tutorial a footprint of a building is added to the breakline layer and defined as a hole in the mesh. However, when running BASEmesh to generate the quality mesh, the hole in the mesh gets much bigger than the building. The entire region between the mesh boundary and the closest breakline (top of bank?) is excluded from meshing.

I have tried doing the exercise two times - same result each time.

I have also run the meshing using the "cheat files" provided with the exercise, i.e. the files in the folder "additional-files". (I have not edited these files, just used them as input when running BASEmesh".)

Same result: The hole in the mesh is much larger than defined by the building footprint.

The same problem has been reported earlier on the forum, and was explained as improper snapping. But the user reporting the problem never confirmed that the problem was solved.

I dont believe lack of snapping can explain the problem. It does not work with the files in "additional-folders", and they have not been edited by me.

Any suggestions?

Marulke

maarnold

Advanced_User

Registered: 2014-09-13

Posts: 29

Re: Tutorial 1, the hole boundary does not work properly?

Hi,
I've just checked the tutorial and it did work for me (additional files).
You could check the following points:
* all layers should have the same projection
* do not overwrite "shapefile output" in "quality meshing", always assign a new name for the shape files
* check that you have the correct layer as "model boundary"
* In "optional layers" activate "holes" and specifiy the correct point layer

I had the wrong "model boundary" activated in my first run. For my second run, I had to specifiy a new name for the "shapefile output". The second run was successful.
hope this helps

Marulke

User

Registered: 2015-11-14

Posts: 24

Re: Tutorial 1, the hole boundary does not work properly?

Thank you for your feedback.

Regrettably, I am still not able to get the correct results.

I have tried once more, but the result is the same. The hole in the mesh is not following the building footprint, but instead the closest top of bank line.

I made a pdf file with screenshots of what I did. If you are interested you will find it here: https://www.dropbox.com/s/8z5rzsq0c5tav … 1.pdf?dl=0

Thanks,
Marulke

maarnold

Advanced_User

Registered: 2014-09-13

Posts: 29

Re: Tutorial 1, the hole boundary does not work properly?

Hi

I checked the tutorial again and found the reason. It is the lack of snapping! The start and end vertices of the breakline which describes the building are not properly snapped. If you resnap the two vertices of this breakline with QGIS (snapping options activated with appropriate tolerance) you will be able to create the desired mesh.

good luck

Marulke

User

Registered: 2015-11-14

Posts: 24

Re: Tutorial 1, the hole boundary does not work properly?

Great,
now the mesh is as it should be.

As I never edited the "breaklines_qual_mesh"-file the (lack of snapping) problem is in the exercise file?

Great help, thanks
Marulke

Stephan Kammerer

Developer

Registered: 2015-03-31

Posts: 67

Re: Tutorial 1, the hole boundary does not work properly?

Dear BASEmesh users,

thanks for identifying this problem with our tutorial data! The problem is related to the internal snapping tolerance of QGIS respectively the distance how far two point coordinates may be located away from each other to still be considered at the same location. This tolerance may vary depending on QGIS versions or also if a shp-file has been create in another GIS software (e.g. ArcGIS).
For that reason, the user will be able to adjust this relative snapping tolerance in the new version of BASEmesh coming soon! So far please redo the snapping of the building shp-file as kindly mentioned by the user above.
In general, proper snapping is very important when using BASEmesh. If anything doesn't work as expected, it is always the first step the check the snapping.