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Topic: Image cropping issue

Hi all
I am experiencing the following problem. I wanted to subset a couple of areas from two HiRISE images (usgs jp2 ortho and raw). Before doing the tie point selection I've cropped the images in envi (spatial subset) and I've saved them in envi format. Then I've performed the tie point selection (image to image) over the cropped data and I've saved my tie point file. Then I launched the Tie point to GCPs receiving this error message "Tie Point ... is outside DEM coverage - Altitude set to 0.0". However, I carefully checked the tie points and all of them are inside the DTM boundaries. Do you have an idea on what's going on? I guess something went wrong in the cropping phase.
Thank you very much and happy new year

Simone

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Re: Image cropping issue

Hi Simone,

this problem refers to Note 1 in "Tie points Selection", p19 on the COSI-Corr User guide.
ENVI keeps track of the cropping that you do. When you use the tie-point selection tool (an ENVI tool) on a cropped image, the pixel coordinates of the tie-points that you select are with respect to the original image and not the cropped one. For instance if you cropped an image starting a x=200 and y=200, then when you select a point in the cropped image at the top-left location, its pixel coordinates saved in the tie-points file will be (200,200) and not (0,0). COSI-Corr does not keep track of this.
If you cropped an image before tie-points selection, make sure to set the xstart and ystart in the header of the cropped image to 0 first. Either by manually editing the .hdr or  right-click on the image in the "available band list" widget.

Francois

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Re: Image cropping issue

Hi Francois
So I should do this:
1)Crop the images
2)Edit the header of BOTH (ortho and slave) images by setting xstart and ystart to 1
3)Tie point selection
Is everything right?
Thank you very much

Simone

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Re: Image cropping issue

yes you can do that. Once you updated the xtart and ystart. Close and reopen the file to make sure the changes are accounted for.

Now, remember that you should NOT crop a raw image that you intend to process (optimize and orthorectify) with COSI-Corr. If you do so, the metatdata which contains information with respect to the full raw image will be out of sync with the cropped image. Cropping of a raw image occurs when you select the output footprint during the orthorectification.

Francois

5 (edited by silvestro 2016-01-07 10:15:15)

Re: Image cropping issue

So the aim of the cropping is to improve the co-registration in one specific area. Also, I am working on dune areas and I want to cut out non-dunes zones (it is much easier to work with smaller subsets, at least for me). Can I accomplish that by cropping the ortho image only and then spread all the tie points in the subset covered by the cropped ortho?
If not, how should I do that?
Thank you

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Re: Image cropping issue

yes, you can do that.
Francois

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Re: Image cropping issue

Ciao Francois
I did it, and I the co-registration between the cropped images ended up really well.
Thank you very much

Simone