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World Files

June 19 2009 | 0 comments
Categories: Map Data

I have downloaded an aerial image from TerraServer toady. The world file says that it should be in WGS 84 UTM Zone 16. Yet when I look at the properties of the jpg or tif, the spatial reference is undefined. More so, if I define the jpg or tif using define projection or by right clicking on the layer and defining the projection, nothing happens. The coordinates stay the same and the file does not fall into place. I am trying to insert this aerial image into an existing document that has the coordinates defined. This is also the case when I project the jpg or tif.
Any suggestions as to how I can define/project this file into the correct postion/coordinate system. Thanks.

Mapping Center Answer:

It sounds like you are having a problem with getting the projection definition to "stick" to the image. This could be the case because the header file for a TIF image could have up to 600 potential tags set in it. The settings of the tags in the file header can actually prevent the spatial reference from "sticking" to the image.

Try defining the projection in ArcCatalog (as you say, either right clicking on the file or using the ArcToolbox tool) and then after you have set the new definition, click on the name of the file and click F5 to refresh the window. Then click on the name of the folder that the file is in and again click F5 to refresh the window. Close ArcCatalog and then open the image in ArcMap to see if the new projection definition "stuck" this time. Note that this only works if the data are on your local hard drive – it won't work if you are working with data that resides somewhere else on your network.

If that doesn't work, you can try an alternate approach in ArcMap. First load some data into ArcMap that has a spatial reference you know to be good. Then add your image. Now set the coordinate system of your data frame to be the NAD 1983 UTM Zone 16. Since NAD 1983 and WGS 1984 within the 48 contiguous states are within a meter of each other, using NAD 1983 UTM Zone 16 will work as well as WGS 1984 UTM Zone 16N. Once you set the data frame properties to UTM zone 16, your data will project on the fly to that coordinate system. If the image is really projected or georeferenced to UTM Zone 16N, your data should align with the image.

You can simply work in this data frame or if you have an ArcInfo level license for the software, you could right click the image and export it using a different file format than the TIF or JPG format that the data are currently in. The exported image should have the correct projection definition.

If none of this works, try calling ESRI Support!

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