[GRASSLIST:2366] Re: Problems with projection conversion of vector files

anne-claire serres anne-claire.serres at thales-is.com
Wed Aug 22 06:05:36 EDT 2001


I projected the lat, long vector file in UTM without problems. So, the v.proj seems
working perfectly.
The problem appears with the lambert conical conform projection : the units usually
used are grades and meters but in Grass, I don’t know what are the default parameters.

First, I try a lambert II projection that wasn’t working.
So, I try a Lambert-93 projection using degrees as it seems that grades are not

Projection :lcc
Ellipsoid : clark80
Latitude origin : 46,5°
Longitude : 3°
1er parallel : 44°
2ème parallel : 49°

False Easting = 700 000 meters
False Northing = 6 600 000 meters

Datum non defined

The region generated is in the attached file.

When I tried to display the projected file : a G_malloc error appeared. I do not
understand it because the vector file is quite small.
So, do you think I need to hand-edit the WIND and DEFAULT_WIND as you did ? Is there a
way to know about how is 'made' the lcc projection, with which parameters ?


Rich Shepard a écrit :

> On Fri, 17 Aug 2001, anne-claire serres wrote:
> > the map is displayed in the monitor but the region's coordinates (and so
> > the vector map) are totally wrong (see region.jpg attached file).
> > So, I search why and I find that when it creates the dig file (see
> > location.jpg attached file), it creates North = 5 (and I don't know the
> > unit) instead of 60 grades and south = -64 instead of 44 grades.
> >
> > I think I miss something, perhaps when the "v.support" is automatically runned ?
> Anne-Claire,
>   I do not think that v.support should be necessary after reprojecting an
> existing GRASS vector map. That module will build topology after importing
> from a different format. If it is run automatically, theoretically it should
> make no difference -- particularly with the region's boundary.
>   What units and values should define the area of your map? I have had to
> hand-edit the WIND and DEFAULT_WIND files to get the coverage necessary for
> the maps to be properly displayed.
>   IIRC, you converted from geographic coordinates (lon/lat) to a projection,
> correct? I had problems with r.proj recently and I wonder if similar
> problems exist with v.proj. Others with better ideas than I need to step in
> here and offer some help. I, too, am interested in the solution.
> Rich
> Dr. Richard B. Shepard, President
>                        Applied Ecosystem Services, Inc. (TM)
>             2404 SW 22nd Street | Troutdale, OR 97060-1247 | U.S.A.
>  + 1 503-667-4517 (voice) | + 1 503-667-8863 (fax) | rshepard at appl-ecosys.com
>                  Making environmentally-responsible mining happen.
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