projections in GRASS

Vicente_Sosa · February 27, 1995, 12:35pm

Hi,

has anybody out there any experience transforming raster data
between projections?

In particular, I'm looking for a method to transform Lat-Long DEM
data ( europe from ETOPOS5 ) to a conic projection ( say, Lambert ). I need
this to feed the transformed height data to a 3d rendering package (
renderman ) to generate an orthographic zenithal view that will be
incorporate as background to a vectorial postscript map.
I know how to transform GRASS vector data between projections using MAPGEN,
but I haven't found any reference to this problem with raster maps.

Is there a solution to this problem inside GRASS ( or outside )?
I would very much appreciate any help.

Please, send the answers directly to me. I don't know why, but I can not
subscribe grassu mailing list!

Thanks in advance!

vic
*--------------------------------------------------*
* Vicente Sosa, Grupo Anaya *
* J. I. Luca de Tena, 15 - 28027 Madrid, Spain *
* tfno: 34 1 320 01 19; fax: 34 1 742 66 31 *
* e-mail: vsosa@anaya.es APPLELINK: SPA0263 *
*--------------------------------------------------*

Bart_Cosyn · February 27, 1995, 5:08pm

Hi,

Hi,

has anybody out there any experience transforming raster data
between projections?

As Grass is not transformable from f.i Non-projected data to Lambert
Conic projection I am a bit afraid you will need to combine own written
programs with the Grass tools for image processing. i.points and i.rectify

I had a basically identical situation to transform my data to the Belgian
Lambert projection.
I wrote a program that allowded me to calculate points from one system to
another. This you should be able to get from a local geographic institute
or at least you would need to have the refernce points and meridian.
After having written this you should do the following.

Make a group with i.group so in this way grass creates the subdirectory
group and a subdir with the name of the group. Normally using i.points or
i.vpoints you create a file POINTS. You can skip the module i.points and
create the file POINTS yourself with your calculated data. Then just run
i.rectify. Be sure that you have good distributed points over the area.
It should work but it will take time to develop your own transformations!

Bart