[GRASS5] raster georectification

Kirk R. Wythers kwythers at umn.edu
Wed Jan 7 10:24:50 EST 2004

I have a set of scanned maps that I want to georectify. However I am 
unsure of the most efficient way to handle the three images (three 
color bands) associated with each image. I have imported them into a 
temporary xy location and can display with d.rgb (takes about 10 
seconds to display). I have grouped all with i.group, and used i.target 
to set up new target location and mapset. Now I am ready to use 
i.points. My question is this: Since it looks like all three element 
maps (rgb) need to have i.points run with associated coordinates, 
should the three elements of the color table me merged first in order 
to reduce the number of maps that need georeferencing, or is assigning 
coordinates to all three bands the standard approach?  I read in "Open 
Source GIS: A Grass GIS Approach (Neteler and Mitsova) that one of the 
reasons that scanned color maps are broken into color bands is to 
reduce computational overhead and there by speed up image processing. 
Does it make sence to merge these maps first in order to reduce number 
of maps that need georectifying, or would I be more than paying for 
that time savings with very slow image processing?

btw... using grass5.7


Kirk R. Wythers	                                     tel: 612.625.2261
Dept. of Forest Resources                 fax: 612.625.5212
University of Minnesota      email: kwythers at umn.edu

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