[GRASS-user] Reprojection from LLC to UTM (various zones)

Miriam España mespana at ugr.es
Mon Aug 27 06:48:40 EDT 2007

Hello again,

yes, Maciek, I'm visualizing 3D voxels map, that are in lcc proyection,
covering the next area:

north: 48.070938 (degrees)
south: 21.178000 (degrees)
east: -68.766000 (degrees)
west: -109.461250 (degrees)
top: 14551.891 (meters)
bottom: 36.294 (meters)

from an ascii 3d file. I have a DEM (500 km resolution) that covers all the
world, that I can see in Nviz (sometimes the corners of the dem are lost in
the infinite).

I visualize a volume over the orography (dem).

Sometimes, nviz crashes, but the reason to transform maps from lcc to utm is
because of the visualization of the isosufarces is not correct in lambert,
and it was suggested to me in the irc, that nviz can't manage voxels 3d in 
lcc, only XY or maybe UTM. I don't know if how nviz visualize the isosurface
is the problem. I know that uses the marching cubes algorithm, but I don't
know if it's or not dependent from the projection.

In fact, when I tried to visualice the volumen directly in UTM (not
reprojecting from lcc to utm), the result is different, but the map is
greater that the area that utm zone can cover (not the region, the region is
set with g.region rast3d=map... its ok) and it's logical that it doesn't
work... the volume in this case isn't continuous (and really it is).

I check the isosurface versus  vis5D (I know it's old software).

Maciej Sieczka wrote:
> Michael Barton wrote:
>> Actually, NVIZ DOES handle such maps OK. You have to mess with the
>> z-exaggeration setting a bit, but you can display latlon maps in 2.5D. A
>> real plus for GRASS over other GIS and visualization systems.
> Please correct me if I'm wrong, but Miriam wants to visualise a 3D
> raster I guess (as she wrote), not a 2.5D one. Moreover, LCC projection
> is not in degree units, so it should not be neccessary to play with Z
> exag in any special way.
> Miriam,
> What is the issue with NVIZ in details? As of now NVIZ in GRASS 6.2 and
> 6.3 tends to crash on 3d rasters (volumes). Is that the origin of your
> problem?
> Maciek
> _______________________________________________
> grassuser mailing list
> grassuser at grass.itc.it
> http://grass.itc.it/mailman/listinfo/grassuser

Gynn Clemments wrote:
> Gynn Clemments wrote:
>>That's incorrect; NVIZ doesn't care about the projection.

Then, doesn't matter where I try to visualize a volume? In the process to
reproject the volume from lcc to utm, the number of rows and columns varying
because of the reprojection, in utm the distorsion increments to the north,
and the voxels  does  the same .

Thank for your pattient.

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