I have recently redoubled my efforts to get my installation of the WinAPRS mapping application fully configured with as many maps and database files as I think could be of use for general Ham radio use and emergency use in particular. I have loaded the latest TIGER maps for roads, political divisions and so on; the ancient USGS DEM files for the color terrain map, and various locations (EOCs, Red Cross sites, etc.), and a few other things.

My longstanding desire has been to overlay the current NEXRAD weather radar over all of this, but I have long been stymied by the seeming absence of imagery that was ready-made for GIS-type overlays. It seemed as if this would be impossible to achive, until I found something that is but one painful step away from working.

Everything I had found previously had the radar, plus a raster map that had everything else in it (terrain, roads, polititical divisions, rivers, etc.) that I already had better versions of, and the presence of in the radar image would obscure far too much. It appeared that I would have to track down the raw radar data and then reassemble it into a georeferenced transparent image (something currently beyond my programming skills).

I was just about to give up when I stumbled across a more sophisticated National Weather Service weather radar mapping Web page–one that included each element as a separate image. Further investigation revealed a page dedicated to weather radar for GIS users, describing how to find exactly the image for a particular region, weather radar, or the counterminous United States! And each image was a transparent GIF with an ESRI-style World File. I thought I was home free, for a few minutes anyway. Note to the NWS: Your use of the ampersand in URLs creates links that are invalid HTML when pasted into Web pages. Please use the semicolon instead to separate arguments, as the Web standards require.
But you knew it was coming–the failure of an application to support important standards that have been around for years. WinAPRS does support the inclusion of georeferenced images (including pulling them from Web URLs), but does so using a so-called GEO File Format that I have not seen used outside the Ham radio APRS world. This wouldn’t be so bad if both formats used the same methodology to locate and rotate the image, but they don’t. The ESRI World File maps one pixel in the image to a Lat/Lon coordinate and then specifies rotation and the real-world size of a pixel in the X and Y dimensions. The APRS .GEO file simply maps two pixels in the image (which must be near the top left and lower right) to two Lat/Lon coordinates. Further complicating the problem is that the NWS radar image is referenced to NAD-83 and WinAPRS uses WGS-84.

The correct solution is for WinAPRS to support the ESRI World File for placing images, but if I can’t get that to happen, this will be an interesting exercise.