[Xastir] More on radar problem

[Alex Carver]

--- On Sun, 12/6/09, James Jolin <jjolin at itol.com> wrote:
> Alex,
> How did you set up the geo file?  Did you take an
> existing file and change the url or did you start from
> scratch?  I know next to nothing about geo files.
> Jim
> WA9ARB

The easiest way is to follow along with one of the default GEO files and make the appropriate modifications.

Here's an example of my GEO for the Atlanta area RIDGE radar (watch out for word wraps):

#                       X               Y               Long            Lat
URL     http://www.srh.noaa.gov/ridge/RadarImg/N0R/FFC_N0R_0.gif
TIEPOINT                0               0               -87.37500       35.58083
TIEPOINT                620             620             -82.00217       31.14133
IMAGESIZE 620 620
REFRESH 60
TRANSPARENT 0x0
PROJECTION LatLon

The TIEPOINT directives will assign a specific pixel coordinate (X,Y) to a specific lat/long.  Pixel 0,0 is upper left, and 620x620 is the lower right most pixel on my RIDGE image (the image itself is also 620x620 in this case).  You need two TIEPOINTs so that Xastir can appropriately place the image.  The IMAGESIZE tells Xastir how big the radar file is in pixels (again 620x620 for the Atlanta RIDGE).

After that, just fix the URL accordingly.

The more accurate the points, the better the radar will line up with your maps.  I used Delorme Street Atlas to find a couple known points in the RIDGE data and then worked my way back to the corners.  You don't have to use the corners of the image file, any two points will do since Xastir knows about the overall image size using the IMAGESIZE directive.

You may have to play around with the TRANSPARENT directive which tells Xastir what color is defined to be transparent for overlay purposes.