Triangle Mesh: Difference between revisions

From GRASS-Wiki
Jump to navigation Jump to search
(new FAQ)
 
(more)
Line 2: Line 2:


'''A:''' You can import the triangular mesh as a vector file by first importing the nodes with v.in.ascii and by creating a three column table (as you have three water elevation values) linked to the id number of each node. To create the triangular mesh run v.delaunay.
'''A:''' You can import the triangular mesh as a vector file by first importing the nodes with v.in.ascii and by creating a three column table (as you have three water elevation values) linked to the id number of each node. To create the triangular mesh run v.delaunay.
''TIN'' data is really just point data with lines drawn between points. So if you can extract the x,y,z coordinate at each node you can build a much nicer raster surface than a TIN using one of the v.surf.* modules.
GRASS raster maps work on a 2D grid of cells with constant North-South and East-West resolution (but NS and EW resolutions may differ). If the highest resolution data would make your raster unmanageably large, you can zoom in to a small region to make the higher res map, then create additional medium and coarse resolution maps at a wider zoom level. Finally you could switch back to the fine resolution and display all three maps overlaying each other. GRASS will over-sample the low-res maps as needed.


[[Category: FAQ]]
[[Category: FAQ]]

Revision as of 08:26, 22 April 2008

Q: I have some coastal data that is in the form of a triangle mesh where the triangles are of different sizes. The triangles are subdivided the closer they get to the coast. Each vertex in the triangle set holds the water height at that location. Each vertex also has a lat/lon associated with it. I want to get this data into GRASS, how?

A: You can import the triangular mesh as a vector file by first importing the nodes with v.in.ascii and by creating a three column table (as you have three water elevation values) linked to the id number of each node. To create the triangular mesh run v.delaunay.

TIN data is really just point data with lines drawn between points. So if you can extract the x,y,z coordinate at each node you can build a much nicer raster surface than a TIN using one of the v.surf.* modules.

GRASS raster maps work on a 2D grid of cells with constant North-South and East-West resolution (but NS and EW resolutions may differ). If the highest resolution data would make your raster unmanageably large, you can zoom in to a small region to make the higher res map, then create additional medium and coarse resolution maps at a wider zoom level. Finally you could switch back to the fine resolution and display all three maps overlaying each other. GRASS will over-sample the low-res maps as needed.