[GRASSLIST:8898] Re: orthorectification of Quickbird satellite images

[Dan Gavin]

Ian,
Thanks for the comment.  My reading and experience with i.points and 
i.rectify is that is does a rectification for planar surfaces, but 
can't take terrain displacement into account.  i.ortho.photo does use 
a DEM in conjunction with rectification, but it is tailored to aerial 
photos, not satellite images.  Low elevation satellite images (> 20 
degrees from nadir) accentuate the effect of topography.

Dan

At 5:20 PM -0800 11/4/05, Ian MacMillan wrote:
>Dan, I am not sure about i.points3, but i.points and i.rectify does 
>work.  I think you will still need a higher resolution DEM for your 
>elevation correction (depending on the resolution you want for your 
>satellite imagery).  Those are sometimes hard to obtain for large 
>parts of the world.
>
>Hope this helps,
>Ian
>
>
>On Nov 4, 2005, at 3:42 PM, Dan Gavin wrote:
>
>>
>>Hello all:
>>
>>I would like to orthorectify some high-resolution Quickbird images, 
>>taken 20 degrees off-nadir.  They are in a mountainous region, and 
>>I need fairly high positional accuracy.  While these images are 
>>distributed as geoTIFFs, elevational distortions have not been 
>>removed (their ortho product is based on a 90 meter DEM). 
>>Searching the list archives, I see a suggestion to use i.points3 
>>and i.rectify3.  Are these functions available in GRASS 6.1?  Any 
>>other suggestions, including other software?
>>
>>Many thanks,
>>
>>Dan
>>
>>--
>>Dan Gavin
>>Research Associate
>>University of Vermont
>>Botany and Agricultural Biochemistry
>>120B Marsh Life Science
>>109 Carrigan Dr.
>>Burlington, VT 05405-0086
>>
>  >
>>
>What happens if a big asteroid hits Earth? Judging from realistic 
>simulations involving a sledge hammer and a common laboratory frog, 
>we can assume it will be pretty bad.
>  - Dave Barry
>
>
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-- 
Dan Gavin
Research Associate
University of Vermont
Botany and Agricultural Biochemistry
120B Marsh Life Science
109 Carrigan Dr.
Burlington, VT 05405-0086