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

Miriam España mespana at ugr.es
Tue Aug 28 05:29:33 EDT 2007

Maciej Sieczka wrote:
> Miriam Espan~a wrote:
>> 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)
> lcc units are not degrees. What does the "g.region -g" and "g.proj -p"
> say?


GRASS 6.3.cvs (Lambert2):~ > g.region -g
GRASS 6.3.cvs (Lambert2):~ > g.proj -p
name       : Lambert Conformal Conic
datum      : nad27
towgs84    : -22.000,157.000,176.000
proj       : lcc
ellps      : clark66
a          : 6378206.4000000004
es         : 0.0067686580
f          : 294.9786982000
lat_0      : 36.0000000000
lat_1      : 60.0000000000
lat_2      : 30.0000000000
lon_0      : -85.0000000000
x_0        : -61.8400000000
y_0        : 19.0000000000
unit       : meter
units      : meters
meters     : 1.0
GRASS 6.3.cvs (Lambert2):~ > 

It's a concept error from me. I've imported the dem with r.in.bin form
-180,180,90,-90, and, for this reason, 1 degree is equivalent to a meter in
my location. Because of that, when I put coordinates as if it would be
lat/long coordinates, I see the part of the world I expected, I supposed. I
didn't realized this (thanks). 

Maciej Sieczka wrote:
>> from an ascii 3d file. I have a DEM (500 km resolution) that covers all
>> the
>> world,
> The whole Earth in a conic projection? Something's wrong here.

No. I imported a DEM with r.in.bin. I  know that the original map I try to
perform in GRASS covers the region above in a lcc projection with those
parameters, and I only want to see this part of the world (but the file I've
got covers all the world, independent of the projection (it's a binary

Maciej Sieczka wrote:
>> 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.
> As Glynn already has pointed out, that's not correct.
> Maciek
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Ok... then, Nviz is independent from the projection. But, then, how can i
georrefer a volume? I know that the ascii 3d volume has been calculated with
a projection (it's derivated from Vis5D), but, falling apart with this, the
secuence steps to solve my problem can be like this ¿?:

1- Import terrain from the file in a XY location
2- set the region to the area i try to see
3- extract that area in other map
4-reproject the new map to lcc
5-import the volume without projection in lcc

Then, I must check before that volume and new map of the area has the same
2D dimensions (not adjust with g.region... only g.region t=Top b=bottom, to
visualize the volume)...
I'm going a little crazy with this task. Thanks to all for all your
patient... sorry so much for the inconvenience. Any suggestion to resolve it
would be appreciate.

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