[GRASS-dev] convert 3D polygons or Tins to a DEM?

[Markus Neteler]

On Jan 21, 2008 7:59 PM, Helena Mitasova <hmitaso at unity.ncsu.edu> wrote:
> On Jan 21, 2008, at 11:23 AM, Markus Neteler wrote:
> > On Jan 21, 2008 4:22 PM, Martin Landa <landa.martin at gmail.com> wrote:
> >> 2008/1/21, Martin Landa <landa.martin at gmail.com>:
> >>> 2008/1/21, Markus Neteler <neteler at osgeo.org>:
> >>>> 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)

Markus