[GRASS-user] Projecting and georectifying in GRASS

[Ned Horning]

I have a few questions about projections and image-to-image 
georeferencing in GRASS. I'm using GRASS 6.4 from the weekly build a 
couple weeks ago on my Ubuntu computer.

Is it possible to import an image and project it in one step? The method 
I have been using is to run gdalwarp from the target GRASS environment 
so the target projection is specified automatically but that creates an 
image outside of GRASS that needs to imported in a second step. The 
other method that I read about is to use two Locations, one for the 
source and another for the target image. That also requires two steps. 
It seems as if there should be a way to project an image as it is being 
imported - maybe even as an option if the projection of an image to be 
imported is different from the GRASS location but I haven't been able to 
find it. Then again it looks like gdal isn't able to output GRASS images.

To do the image-to-image registration I want to take two images that are 
in the same projection but not well aligned and warp one of them to 
match the other. I was planning to use the Georectifier GUI for this but 
have run into a problem. If I understand the functionally I should be 
able to pick a source GCP by clicking on the XY map window and then 
click on a corresponding point in a “normal map display” window to enter 
the target GCP. By “normal map display” I assume the help file is 
referring to the map window that open when GRASS starts up. If I load 
the target image in the normal display before launching the Georectifier 
GUI the image displays fine but after launching the Georectifier tool if 
I try to zoom in on the image in the normal display or click on it to 
select a target GCP the display canvas goes blank (white). If I try to 
display an image in the normal display after starting the Georectifier 
GUI the display canvas remains blank. Is this a bug or am I doing 
something wrong?

Is it possible to use an RGB image for the image that is displayed in 
the XY map window (the window holding the source image that launches 
with the Georectifier GUI)? I could only seem to display a gray scale 
image but maybe I am missing something.

Is there an easy way to enhance an image in a display window. It can be 
convenient to rescale the pixel values to enhance certain objects for 
picking control points but I'm not sure how best to do that. The only 
way I'm aware of is using r.colors.

Thanks in advance for any help or advice.

Ned