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[aprssig] Geo Files

Bill Diaz william.diaz at comcast.net
Sat Feb 25 23:50:18 UTC 2006


Pete,
  See below:

>-----Original Message-----
>From: aprssig-bounces at lists.tapr.org 
>[mailto:aprssig-bounces at lists.tapr.org] On Behalf Of AE5PL Lists
>Sent: Saturday, February 25, 2006 14:54
>To: TAPR APRS Mailing List
>Subject: [aprssig] Geo Files
>
>
>I can generate a table similar to
>http://www.aprs-is.net/wx/RIDGERadar.asp with the points needed for a
>Geo file (0,0 & 599,549).  However, I need to know: are the lat/lon
>coordinates used for the center of the pixel or the top/left,
>bottom/right corners of the pixels?  I am guessing that most people use
>the center of the pixel but I would like this confirmed.


The regular ridge world files reference the center of the pixel in the upper
left.
If you look at http://www.srh.noaa.gov/ridge/GIS.html it includes the
following information:

Each of the RIDGE radar image has a "world file" associated with it. A world
file is an ASCII text file associated with an image and contains the
following lines:

Line 1: x-dimension of a pixel in map units
Line 2: rotation parameter
Line 3: rotation parameter
Line 4: NEGATIVE of y-dimension of a pixel in map units
Line 5: x-coordinate of center of upper left pixel
Line 6: y-coordinate of center of upper left pixel

The above clearly states "center of upper left pixel".

Bill KC9XG

>73,
>
>Pete Loveall AE5PL
>mailto:pete at ae5pl.net 
>
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