Hi Helena and others. Unfortunately 3D vector ignorance isn't the only problem of v.delaunay - it still (as of 6.3.0RC4) fails to work correctly with more than 32XXX vector points [1] - thus making it not an option for large datasets. Yesterday I looked on v.delaunay source and unfortunately understood, that my C skills are too poor to fix it. :(
Fixing large dataset and 3D support problems would be a nice improvement of GRASS vector support :) Maris. 1. http://wald.intevation.org/tracker/index.php?func=detail&aid=335&group_id=21&atid=204 2008/1/28, Helena Mitasova <[EMAIL PROTECTED]>: > > On Jan 25, 2008, at 2:46 PM, Markus Neteler wrote: > > > On Jan 21, 2008 7:59 PM, Helena Mitasova <[EMAIL PROTECTED]> > > wrote: > >> On Jan 21, 2008, at 11:23 AM, Markus Neteler wrote: > >>> On Jan 21, 2008 4:22 PM, Martin Landa <[EMAIL PROTECTED]> > >>> wrote: > >>>> 2008/1/21, Martin Landa <[EMAIL PROTECTED]>: > >>>>> 2008/1/21, Markus Neteler <[EMAIL PROTECTED]>: > >>>>>> can we convert 3D polygons or tins to a DEM? Possibly a job for > >>>>>> v.to.rast... > >>>>>> > >>>>>> v.to.rast help > >>>>>> ... > >>>>>> use Source of raster values: > >>>>>> z - use z coordinate (points or contours only) > >>>>>> > >>>>>> Would it be a big mess to extend that? > >>>>> > >>>>> I guess wouldn't be so complicated to add support also for faces > >>>>> (and > >>>>> 3d lines in general) to v.to.rast... I can try take a look. > >>>> > >>>> just idea, > >>>> > >>>> tin -> > >>>> > >>>> v.to.points -n > >>>> v.clean tool=rmdupl > >>>> v.surf.* -> dem > >>> > >>> well, this would only give an approximation AFAIK. > >> > >> that is right - if you want to preserve the triangle facets in the > >> TIN > >> you need to do linear interpolation using the 3 points of each > >> triangle facet and you get something like this > >> (this is TIN converted to raster in some old version of Arc) > >> > >> http://skagit.meas.ncsu.edu/~helena/gmslab/interp/F1b.gif > > > > > > I discovered that we have tin.c in vectlib: > > > > int > > Vect_tin_get_z ( > > struct Map_info *Map, > > double tx, double ty, > > double *tz, double *angle, double *slope) > > that looks promising - I checked v.delaunay and unfortunately it > ignores the z-coordinate even if you give it 3D vector points - so first > the v.delaunay would have to be updated to preserve the z-coordinates > and write 3D vector map rather than 2D (perhaps not too complicated > task) > and then the simplest way would be just to call the above function > for each grid point > with Map being the 3D vector area map from v.delaunay. > The computation of slope and aspect is missing but adding those > should be easy. > > maybe somebody with better C-programming skills could look at it - > just adding > the z coordinate to v.delaunay would add the missing TIN support to > GRASS > and the result could be visualized as 3D vector, > > Helena > > > > Markus > > _______________________________________________ > > grass-dev mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/grass-dev > > _______________________________________________ > grass-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-dev > _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
