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