[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
Thanks
Kirk
------------------------------------------------------------------------
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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