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I want to understand how "world files" are created. I found some definitions, like:

http://en.wikipedia.org/wiki/World_file

which says that the 2 last lines in the file are x and y coordinates of the center of the upper left pixel. I want to know if those coordinates may be given in decimal degrees? All examples I found gave UTM coordinates without the zone, what means one just cannot know where the image is from!

Am I missing something important here?

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  • See gis.stackexchange.com/questions/61028/…
    – Mapperz
    Commented Apr 20, 2015 at 21:23
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    they can be given in degrees, but it would not make sense to apply those to a UTM image - since the world file affine transform assumes "regular spacing" in x/y (possibly with affine shear) - it's the fault of the data producer to not include basic metadata, you can probably figure it out if they are not forthcoming (is there any other auxiliary files with the data? what are all the files you have?)
    – mdsumner
    Commented Apr 20, 2015 at 21:28
  • Yes, a prj file, that's what has the projection information in it. Sometimes there's an aux and/or XML with extra data. The units for the coordinates and the cell size must be the same, all metres, all feet or all degress. If you don't know seek the information from the source of the image, if you still can't find out take a guess and see how it lines up with known accurate data, normally there's only a few options of what it could be - redefining the spatial reference does not affect the data, just don't project (warp) it until you're certain. Commented Apr 20, 2015 at 22:30
  • Here's a link to a simpler document webhelp.esri.com/arcims/9.2/general/topics/… (yes, it's Esri, but it's not ArcGis specific) Commented Apr 20, 2015 at 22:31

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