BARNES DAVID barnesd at lab.cc.wmich.edu
Sat Jul 1 18:50:43 EDT 1995

Dear Grass-users,
	I don't suppose many U.S. Grass users are out there on this weekend 
but I'm pressing on a project and having trouble with i.points.
	I attempted to i.rectify some air photos using Topo quad determined
UTM coordinates in i.points. Seemed to work O.K. for image #1 with col and
row errors < 20 units (actually image x,y coords are equal to pixels on input
image, ~ 1m) and target error <10. The overall rms error <10m, less than TOPO
sheet resolution -> I'm happy.
	The next image (#2) was processed in the same fashion. This time many
of the col and row errors are over 100 image units but the target errors are
still <10. Both sets of image points in the two i.points exercises (#1 and
#2) were taken from about the same places on the respective air photo so that
photo distortion should be similar and not that bad (not hundreds of feet!).
A third image was similarly processed with the same (bad) results as #2. 
	Both unsatisfactory rectified target images (#2 and #3) produced by
i.rectify misrepresent the input location reference points in the UTM
coordinate system as determined in d.measure "where am i". The locations of
reference points input for image #1 are O.K. in the rectified image.
	The last puzzle is that the two incoorectly rectified target
rastermap images (#2 and #3) do not display the entire input rastermap images
dispite instructions to set default region to be "minimum to contain entire
image" in the i.rectify interactive commands. Any ideas - wise advice?

	Sorry for the long message... but I'm struggling!

  * My Address					           *
  *						           *
  * DAVE BARNES						   *
  * Geology Dept.					   *
  * Western Michigan University				   *
  * Kalamazoo, MI 49008					   *
  *							   *
  * email address					   *
  *							   *
  * barnesd at lab.cc.wmich.edu				   *

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