| 11 Nov 2011 03:20 PM |
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I am trying to select some fiducials to build the RPCs for a photo that I am attempting to orthrectify. I do not have the original image or the camera report for the photos, all I have is the digital tiff. file. I am wondering if there is a way to get around not having these for the photo. Would it be possible to orthrorectify the photos by geo-referencing them if it is not possible to do it via the fiducials? Any expert knowledge would be much appreciated.
My end goal is to create a DEM from them.
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Deleted User
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| 14 Nov 2011 07:41 AM |
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To build RPCs for your images, you will need to have information about the camera, which is usually provided in a camera report for the calibrated camera. If these images were not collected using a calibrated camera, then you will not be able to build RPCs for them. The fiducial marks need to have a known distance between each other on the camera's lense. Do you have points in the image between which you know the distance on the camera lense? What kind of camera was used to collect these images?
If you do not have the necessary information to build RPCs, then you can always georeference the images by picking ground control points, using a map or other georeferrenced image to get the correct coordinates for the points you pick. You can do this using ENVI's tools under Map > Registration. But this georeferencing will not be an orthorectification, and you will not be able to extract a DEM from images georeferenced in this way.
- Peg
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Deleted User
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| 14 Nov 2011 07:44 PM |
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Thanks Peg,
The problem is that I do not have the camera report. These aerial shots are from 1959, so who knows where the camera report might be. It may be possible to recover it, but most likely not. I do know that the original size of the images were 9'x9', and I have a feeling that they were shot with at 108mm focal length (There are some numbers in the top of the photo and 108 is one of them). I think I might have figured out a way to find some fiducial points. I loaded the images in to Photoshop. From there I was able to identify the center of the photo (assuming that these photos are perfectly vertical) and made some measurements to points along the edges of the photos. I think that from the coordinates of these points in mm from the center that I can now build an RPC by associating them with an x,y coordinate in ENVI.
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Deleted User
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| 15 Nov 2011 07:24 AM |
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I don't know that the distance between the fiducial marks on the photo is necessarily the same as the distance between fiducials on the camera. ENVI is expecting you to enter the distance between fiducials on the camera. But you can always try it and see if it works. The problem is that if the results are not good, it will be hard to figure out which of the various assumptions you are making here are wrong. But I don't see any reason not to try.
Good luck.
Peg
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