[GRASS-user] i.rectify and ground-based photos

[Blumentrath, Stefan]

Hi Ken,

I have been working on (and struggling with) this as well and did not succeed yet:
For more info and relevant links see: https://lists.osgeo.org/pipermail/grass-user/2015-August/072881.html

My lessons so far are that one
a) needs to use i.ortho.* modules from GRASS 6.4 for this 
b) you have to have fairly good estimates of you camera angle (roll, pitch, yaw) (and preferably use as much as possible down-facing angles)
c) according to the manual you need at least 16 GCPs, as much as possible evenly distributed over your image, and it does not seem to work with less than that at all.

In my case the main problem was c), as I only had a few objects I could use for GCPs in my camera viewshed and all of them were more or less in the background. So, I was missing elements I could recognize in foreground. Therefore I placed colored sheets of paper in the camera viewshed, which I measured with GPS, so I can match camera coordinate system and geographical coordinate system.

Paul Kelly used a different approach for that task (which I unfortunately did not manage to try yet):
http://www.stjohnspoint.co.uk/work/thesis/

Cheers
Stefan



-----Original Message-----
From: grass-user [mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Ken Mankoff
Sent: 28. april 2016 19:49
To: grass-user <grass-user at lists.osgeo.org>
Subject: [GRASS-user] i.rectify and ground-based photos

Hi list,

Is i.rectify only designed for down-looking aerial photography? Or can it be used for highly oblique imagery too, for example photos taken side-looking from a plane window, or from a mountain-top covering a valley?

Thanks,

  -k.
  
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