Re: [Libmesh-users] Create an unstructured mesh of map of country/region

[Roy S. <roy...@od...>]

On Sat, 6 Jun 2020, Prashant K. Jha wrote:

> Thank you so much for your time in replying to my email. I have been able to create a Delaunay triangulation of the map of the Texas state. How I
> did it is as follows:
> 
> 1. Get the shapefile for the map from http://gis-txdot.opendata.arcgis.com/datasets/texas-state-boundary
> 2. Load this into QGIS application which is free and runs across different platforms.
> 3. Use tool 'Vector->Geometry Tools->Simplify' to get coarse lines. You can control how coarse you want the outer lines.
> 4. Use tool 'Vector->Geometry Tools->Extract Vertices' to create a layer with vertices of the simplified map you obtained in step 3.
> 5. Save the layer corresponding to vertices by 'Layer->Save as'. In the save as option, you can deselect most of the features. Look for option
> 'GEOMETRY' and select 'As_XY' to store the (x,y) coordinates of the vertices. This link was
> helpful: https://gis.stackexchange.com/questions/8844/getting-list-of-coordinates-for-points-in-layer-using-qgis
> 6. Finally, I created the .geo file by reading the .csv file in step 5. The file generated in step 5 has the first and last vertices equal so
> while creating the .geo file I excluded the last vertex. I then ran gmsh on .geo file. 

This is pretty great; thanks for the update!

> I think this is not very efficient but for now it works.

Sounds about as efficient as you could hope for for a one-off use
case.  If you were trying to make meshes for dozens of other shapes
too then at that point I'd look into scripting it.
---
Roy