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I am trying to georeference a largish aerial image (50MB) to some GIS data I have and import it as a background. However the image imports extremely small - so small I cant see it!

I am using QGIS and the Georeferencer plugin. I select about 7 control points randomly across the image and I am using the thin plate spline with nearest neighbour resampling. The error is 0.00768. I have tried several transformation settings and set the target CRS to the project CRS, but get similar results.The control points appear in QGIS in the right positions.

I would appreciate any assistance.

ADDED - A screen shot of the settings used.

enter image description here

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Strange. Can we have a screenshot. –  Nathan W May 8 '12 at 1:30
    
Sorry Nathan, but as I am a new user, I cannot upload images yet. –  boberdorf May 8 '12 at 3:37
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@boberdorf you can upload images TO and then share links FROM imgur.com –  Simbamangu May 8 '12 at 5:37
    
@boberdorf Start a new project, set the SRS to World Mercator (just for testing), try polynomial 1 and 2 set the target SRS also to World Mercartor (SRID 3395) and come back with the results. –  Pablo May 8 '12 at 11:14
    
Hi Pablo, I recieved the similiar results using the method you noted. I tried numerous options to see what would happen, and even tried a different image (lower resolution) but that didnt work. Thanks for the advice –  boberdorf May 9 '12 at 12:04

1 Answer 1

If I understand you, tou want to use an aerial photograph to digitize something or as a background for data. I do not think you can georeference an Aerial photograph with QGis georeferencer. That plug-in works for images with a constant scale. In an Aerial photograph you do not have a constant scale, since this one is related to the flying height and the focal length of the camera used. Flying height varies according the terrain´s topography. Nevertheless, you can try using grass i.ortho.photo procedure. In my experience it does work when Grass is installed in a linux environment. You can not use it in a Windows OS and I do not have Mac experience. Check this out

http://www.grassbook.org/sample2nd/grassbook_2nd_2004_chapter10_aerial.pdf

Hope it helps

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