I now have a reply back from the author or WinAPRS on support for ESRI world files. He is working on it, but has one last problem to figure out before it will work. In researching the standard, I came upon an old problem I learned about many years ago, but which never spent the time to find the proper solution for.

While the full-blown GeoTIFF raster image format includes not only the basic georeferencing information but the projection, datum, and units. The commonly used ESRI-created World File (.jpw for JPEG images) lacks the latter three items, and includes only pixel size, image rotation, and origin.

So, when using a world file with a JPEG, GIF, PNG, or other image that lacks the georeferencing capabilities of GeoTIFF, you must also use a projection file (.prj) that includes all this missing information. This has also been defined by ESRI, and has had several flavors over the years. The original format was a multi-line one, used by Arc/Info 7.x, but that has been replaced by a new .prj format originally defined by the OpenGIS consortium as the Well-Known Text (WKT) format, and has since been revised slightly by ESRI, and it’s not clear if WKT has been updated to match the ESRI changes.

But guess what? The National Weather Service doesn’t include a .prj file with its georeferenced weather radar images. And now that I know about this little item, I suspect that most of the so-called georeferenced files floating around are also lacking this important metafile.