[GRASSLIST:3007] Importing TIFF images.

[Ben Logan]

I downloaded some DOQQs in MrSID format from www.gisdatadepot.com, and
wanted to import them into GRASS.  Before describing what I tried,
perhaps I should say what I want to accomplish just to make sure it
can be done.

I would like to "drape" the DOQQ over a 3D rendering of the DEM of the
same region.  I figured that I could export the DOQQ from the MrSID
viewer as a TIFF image, import the TIFF (with r.in.gdal) to create a
GRASS raster file, and then use NVIZ with the DEM as the elevation and
TIFF raster as the color map.

As some of you know, the Linux version of the MrSID viewer will
only save a TIFF of the currently visible portion of the DOQQ.  I
decided that would be acceptable since my P200 would probably laugh if
I tried to feed it the whole, full-scale, uncompressed DOQQ at once. ;)

So I saved the DOQQ as TIFF with a scale of 1:16, and tried to import
it with r.in.gdal.  Here's what r.in.gdal said:

ERROR: Projection of dataset does not appear to match current location.

       cellhd.proj = 0 (unreferenced)

			 You can use the -o flag to r.in.gdal to override this check.

Does this mean that the TIFF is not georeferenced?  I tried using the
-o flag to r.in.gdal, and it imported ok, but the region didn't match
the one it should have.  I was able to set the region to match the
TIFF with g.region, but then the TIFF had lost all its color, taking
on a color map like the DEM raster maps.

How do I rectify (if that's the correct term) the TIFF, and preserve
it's original color?  Do I use i.group, i.target, i.points, and
i.rectify on the raster map imported with r.in.gdal?  If so, how do I
know what coords to use for i.points?

Thanks, and sorry to have so many questions.

Ben

-- 
Ben Logan: ben at wblogan dot net
OpenPGP Key KeyID: A1ADD1F0

Arrakis teaches the attitude of the knife - chopping off what's
incomplete and saying: "Now it's complete because it's ended here."
		-- Muad'dib, "Dune"