A geo file contains information about how to load an image, and how to calibrate it so that the software can determine the lat/lon of each pixel. The first method loads the file from somewhere on the internet.
#NWS_RADAR_byx BOCA CHICA KEY FL kg5qd 07/04/01
URL http://www.srh.noaa.gov/radar/images/DS.p19r0/SI.kbyx/latest.gif
# X Y Long Lat
TIEPOINT 116 108 -83.322365 26.040407
TIEPOINT 525 517 -80.114967 23.108894
Each line must begin at column 1 (no leading white space). The fields must be seperated by
tabs, not spaces.URL specifies the internet address of the image file. You must be able to take this URL, paste it into your browser, and have only the image appear. In other words, the image cannot be embedded in a file, and cannot require any sort of authentication or interaction.
Any line starting with '#' is a comment and is ignored.
You have to have 2 "TIEPOINTs", these associate a lon/lat with any x/y of the image. The X and Y are in pixels of the IMAGE, the LON and LAT are that LON/LAT values of the POINT specified by X,Y. The more accurate that you have this, the better the image map will work. The second point MUST be to the right and below the first point. It is best to have the first point as close to the top left as possible and the second point as close to the bottom right as possible.
NOTE: The images MUST be ORTHOGONAL, this means that lat/lon grid lines are (or would be) horizontal and vertical. At this time, the only images that can be used in all cgi's are png and gif. jpg may be used on plot.cgi as an experimental feature, however the automatic conversion from the 24 bit jog to the 8 bit gif/png format is often unsatisfactory, and until I find a method that works consistently, I will not be adding this to the other cgi's.
The second form is used when the map file is located on findU. In general you should place the geo and map files on your own server, but if you have a non-copyrighted map, and you think will be of general use or if it is for a public event where you expect a lot of hits, I can put them on my server. (I don't want to get into the business of maintaining a huge map directory, as happened with javAPRS.)
FILENAME usa.png
# x y lon lat
TIEPOINT 10 22 -124.73000 48.490000
TIEPOINT 606 335 -80.430000 25.191000