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[aprssig] Geo Files

Bill Diaz william.diaz at comcast.net
Sun Feb 26 14:11:43 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 21:58
>To: TAPR APRS Mailing List
>Subject: RE: [aprssig] Geo Files
>
>
>> -----Original Message-----
>> From: Bill Diaz
>> Posted At: Saturday, February 25, 2006 8:21 PM
>> Subject: RE: [aprssig] Geo Files
>> 
>> Irregardless of what application is using the Ridge files, 
>> the application should use the map reference provided by the 
>> authors.  Obviously, the Geo Files should use the center of 
>> the upper left pixel as a reference point to calculate the 
>> other needed points.
>> 
>> I offered to provide you the ridge table earlier but you were 
>> not interested.  FindU used the RIDGE table I provided to 
>> generate the needed references.  I would be happy to provide 
>> the table to anyone who requests it.  

>Bill,

>Apparently, you do not understand my original post nor do you 
>understand
>the table that I offered and have now posted with the assumption that
>findU, WinAPRS, etc. use the center of the pixel for THEIR geo 
>files.

You posted:
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?  

Since you were referring to RIDGE files, the answer to your question is
obvious.  The lat/lon of the ridge files refer to the center of the pixel.  

I did not bother to answer the second part of your post:
I am guessing that most people use the center of the pixel but I would like
this confirmed.


>I
>had already imported ALL of the RIDGE world files into a database using
>their statement that THEIR files reference the center of pixel 
>0,0.  The
>issue that you apparently are unable to answer is "WHAT DO 
>PROGRAMS SUCH
>AS WINAPRS, UI-VIEW, AND FINDU ASSUME TO BE USED FOR THEIR GEO FILE
>COORDINATES: CENTER OR CORNER OF THE PIXEL?"  I am sorry to this list
>for the shout, but Bill obviously is clueless as to what this question
>means.  Bill, if you don't know the answer to THAT question, then quit
>making your idiotic, self-serving posts.

Pete, mind your manners.  You are being your usual churlish self once again.


You need to re-read my post.  I answered your first question correctly based
on the reference you provided but did not answer the second question since I
did not know how all applications handle this at the time.

The original WinAPRS documentation does not specificially state the center
of the pixel:
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. 

UiView help file also does not specifically state the center of the pixel:
Input the latitude and longitude of the top left and bottom right corners of
the map, which you should have noted at the time that you created the image.


UiView PMapServer has similar language regarding underlay files.  

The above contain no reference to the center of the pixel.  Therefore, it is
likely these applications do not reference the center of the pixels.  

Bill KC9XG

>I have been working with the RIDGE stuff for a long time and am trying
>to make it easier for OTHER people to use the "lite" images for
>applications that can't work easily with the overlay system.  The table
>is at http://www.aprs-is.net/wx/RIDGEGeo.asp for those that are
>interested in making their own geo files.

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





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