On Jan 21, 2008, at 11:23 AM, Markus Neteler wrote:
On Jan 21, 2008 4:22 PM, Martin Landa <[EMAIL PROTECTED]> wrote:
Hi,
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
If you convert to points and run interpolation or approximation
you can get various surfaces e.g. this
http://skagit.meas.ncsu.edu/~helena/gmslab/interp/F1c.gif
or this
http://skagit.meas.ncsu.edu/~helena/gmslab/interp/F1f.gif
although for some applications the interpolated surface is preferable
to get rid of various artifacts created by TIN and create a
continuous surface,
there are applications that include designed features and structures
where
TIN was used in the design and you need to preserve the breaklines
defined by the TIN.
I am not sure whether this should be part of v.to.rast - maybe a
separate
module (v.surf.linear) that would also compute the slope and aspect
map for each facet would be more appropriate,
Helena
I realize that it is easy with (inclined) triangles but less so
with whatever-polygons (are that always faces or could it be
a more complex form?).
Markus
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