Orto correction of aerial photographs
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I wonder whether anybody has experience of work along these lines:
We intend to buy around 20 aerial photographs from the 60's to produce a base material for historically oriented rough modeling of buildings in our area. To do so, we should be able to transform the photographs and connect them to form an image of the area where one photo connects well to the other.
Assuming that the photographs were taken perpendicularly (straight downwards from the aeroplane), we would still need to take into account the fact that the outer edges of the photo are further away than the ones in focus. So apparently the outer edges should be stretched in order to connect with the neighboring picture.
We know that the professionals have software to make this kind of a correction, but I guess that some member of this community could have experience of this kind of a problem. Do you know of a method to stretch the material in a way which could be used as a replacement for that expensive orto correction procedure, which isn't within our reach. - Any ideas?
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Philip,
If you really liked to have a good result, I would still get a firm which deals with such things to do the correction. You may not have the resources for the whole software but who has the software (and experience), could still do it for you within your reach.
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@unknownuser said:
... could still do it for you within your reach.
Sounds reasonable. Is that a guess or do you have experience of such processing?
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Not me. I have a colleague (in the archaeology field) who regularly takes aerial photos of sites and uses such a technique - with his own software etc.
If you wish, I can PM his email address to you. Asking is definitely free.
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Yes, please do so. We would anyway of course get the material in digital form, so crossing borders isn't an issue - maybe an asset.
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OK, PM sent.
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Hi,
that could be the photogrammetry software you need. Is also used in archeology. Cost is about 400€:
At this side you will also find the full Airphoto Manual as pDF. There is a trial version
Charly
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If the aerials were shot with a rectilinear lens (straight lines are straight instead of curved) and if it was pointed directly down then the distance represented by an inch on the edge of the photo would be the same as the distance represented by an inch at the middle. A a square would look like a square anywhere it occurred. If things are skewed or curved, then you need some correction. If you do need correction it is important to get an outcropped photo, or if it was cropped at least know exactly how it was cropped so you can re-create the center of the photo.
The kind of correction that I think of as being unique to aerial photos, vs. correction for panoramic stitching is ortho correcting for tall buildings, taking the top of a tower that looks like it is outin the street and putting it back directly where it should be. At the same time you recover the missing street element from another aerial and fill in the hole. In an ortho corrected photo you wouldn't see the sides of any buildings, just tops.
Third page on this PDF shows a before and after aerial
http://www.sanborn.com/Pdfs/Article_Stand_Straight_Up_2001.pdf -
Thanks guys for the highly interesting material. I'll follow up all these interesting and hopefully helpful hints.
It's nice to see how well this community can respond to various SU-related needs - even in case they are at quite some distance from the main topic.
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