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I have UAS imagery (jpgs) that I have generated .jpw files for. The .jpw files are correct, however now I want any easy way to assign a projection to my images. I know you can do it in ArcMap using the Define Projection and Project Raster tools but I was hoping to just be able to generate a standard .prj file that ArcMap will read automatically when I import my jpg like it does with the .jpw file. Is that possible? I generated a .prj file from an online source: http://spatialreference.org/ref/epsg/32603/, which looks like : this

I made sure the name of the image is the same name as the .prj file. GlobalMapper will read the .prj file but ArcMap will not, is there a reason for this?

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  • I can say a qualified 'yes', ArcGIS does read PRJ files for the formats that I have used. If you use define projection an AUX file will be generated not a PRJ but if one exists, in my experience, it will be read if ArcGIS can read and interpret the information. Define projection does not take long to run but project raster creates a new raster and will take a long time... if you're going to generate and copy files it would be better if you copied (with appropriate name) the JPG.AUX file assuming all rasters have the same number of bands and data type.
    – Michael Stimson
    Commented Jun 19, 2017 at 22:15
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    Welcome to GIS SE! As a new user please take the tour to learn about our focused Q&A format. Did you try using a PRJ with your JPG? What happened?
    – Midavalo ♦
    Commented Jun 19, 2017 at 22:22
  • @MichaelMiles-Stimson Do you have an example of a .prj file you have used for a raster that ArcGIS read? I made a shp file which generated a .prj file and I copy and pasted that information into my raster .prj file and still ArcGIS won't read it.
    – Kelsey
    Commented Jun 19, 2017 at 22:36
  • This is one that I used for a GeoTIFF PROJCS["GDA94_/_Map_Grid_of_Australia_zone_55",GEOGCS["GDA94_/_Geographic",DATUM["D_GDA_1994",SPHEROID["GRS_1980",6378137.0,298.2572221010,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6283"]],PRIMEM["Greenwich",0.0],UNIT["Decimal_Degree",0.01745329251994330]],PROJECTION["Transverse_Mercator"],PARAMETER["Latitude_Of_Center",0.0],PARAMETER["Longitude_Of_Origin",147.0],PARAMETER["Scale_Factor",0.9996000000],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",10000000.0],UNIT["Meter",1.0],AUTHORITY["EPSG","28355"]]
    – Michael Stimson
    Commented Jun 20, 2017 at 0:38
  • Note that a PRJ file can happily coexist with an AUX file, in such cases my experience is that ArcGIS will read the AUX first and Global Mapper will ignore the AUX. Just make sure they both say the same thing and you won't have a problem.
    – Michael Stimson
    Commented Jun 20, 2017 at 0:42

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Yes, ArcGIS reads PRJ files but the PRJ file is a component file for an ESRI shapefile. https://en.wikipedia.org/wiki/Shapefile Your JPG files will always need to have the associated JPW (world file). You could define a projection for the JPG using ArcCatalog. In this case you get the filename.aux.xml file that Michael is talking about. This file helps ArcMap do projections on the fly so the dataframe does not have to be in the same spatial reference system as the image to draw in the correct location. It will not replace the need for a JGW.

Try this: Open the JGW file with notepad, and open the XML file with a web browser. See how the JGW pixel size and corner coordinates get entered into the XML file? You could use something like Python to create a script to generate this XML file. Alternatively, maybe your software exports to GeoTIFF. A GeoTIFF stores the spatial reference system in the file header and your problem will be solved.

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Prj is for vectors especially shapefiles. Images like jpg require jgw and tiff requires tfw files.

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