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We have several ArcGIS 10 map documents containing fully georeferenced images (projected UTM 16N). We also digitised them by tracing over features in the image into shapefiles. Everything seems to save correctly.

However, when we re-open the map document in ArcMap, the georeferenced image goes completely off scale. It is still rotated correctly, but sometimes it ends up multiple times bigger (or smaller!) than it should be, and is not at the right place.

We are baffled by this phenomenon. Can anyone help with this?

Thanks.

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I have seen that happen with images I georeference in arcmap. If I do it my other software it works fine all the time in arcmap. hmm –  Brad Nesom Jan 19 '12 at 20:31
    
Is it possible that you have a GeoTIFF file that also has an associated (and conflicting) world (.TFW) file? –  Kirk Kuykendall Jan 19 '12 at 22:30
    
You use your data in Arc10. How do store your images? As file or GDB? If .gdb- is it mosaic, raster catalog and in which version your .gdb was created? I remember that there was some issues with pyramids in Arc 10. –  Tomek Jan 20 '12 at 8:37
    
Are you remembering to update the georeferencing after you have achieved an acceptable degree of accuracy? –  Dano Feb 1 '12 at 22:14

2 Answers 2

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Assuming that it is not because you are forgetting to update the file's georeferencing after georeferencing it (so when you close the map all your hard work is lost), I suspect it is down to you .aux file getting out of sync. This problem has been around since Arc 8.x and persists with 10. When you open a raster in ArcMap it creates an .aux file automatically if one does not exist. The .aux file is used to maintain the georeferencing regardless of whether you have a world file or georeferencing embedded in the file header.

A naive example of how the .aux can get out of sync could be thus: Suppose you open your unreferenced raster to look at it. ArcMap spawns a .aux without telling you. Then you remember that you have a world file and copy that into the appropriate directory. Your .aux file is now out of sync with your georeferencing and the world file will be ignored.

If you have a correct world file, exit ArcMap and manually kill the .aux file. When you restart ArcMap your raster should be in the right place. To be on the safe side, I also kill the .rrd file (pyramids) and any .XML files because the aux contains a pointer to the rrd file and you could be compounding the confusion by leaving it behind. If there is no rrd you will be asked if you wnt to create pyramids when you open the raster again, so no harm done there. Killing the aux will correct the problem but often at the expense of having to re-declare your projection etc (see here for a description of the aux) - so be warned (again - the least of your worries compared to having your georeferencing ignored)!

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We had a similar experience a few days ago with our georeferenced imagery appearing "out-of-scale." In our case, they were shrunken down to a couple meters in length/width. After much frustration, we finally noticed that the shrunken images all had the world file extension "tfwx" while the images appearing in their rightful place had the "tfw" extension. After manually changing the extensions back to "tfw" for the shrunken images, they were fixed! I don't understand why this works, but it certainly was a relief for us not to have to re-reference all of our imagery. Hope this helps someone.

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