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[aprssig] Weather graphics

Bill Diaz william.diaz at comcast.net
Sun Oct 14 15:10:55 UTC 2007


Stan,
  See below:

>-----Original Message-----
>From: aprssig-bounces at lists.tapr.org 
>[mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Stan Leeds, KC7EHJ
>Sent: Sunday, October 14, 2007 08:48
>To: TAPR APRS Mailing List
>Subject: Re: [aprssig] Weather graphics
>

>I haven't seen any more comments or answers on this. But just this 
>morning I noticed on my IGate computer running UI-View32 and NWS-Get.
>
>The graphics are at
>http://www.hharc.org/gallery/tempdir/longbox1.png
>http://www.hharc.org/gallery/tempdir/longbox2.png

>It looks like they were generated by the following:
><EACZAA>141300z,SVRTSM,NE_C111,  LINCOLN COUNTY
><AECVAA>141245z,SEVERE_WEATHR,NEC63

Not exactly.  The above are county warnings in the affected area, not the
corrupted polygons you observed.  The red polygon in your first example is
likely a county referred to in one of the above messages.

The APRS object packets containing the weather Polygons are created by WxSvr
from the Lat, Lon points included in the NWS weather warning messages.  The
polygon points are encoded for inclusion in APRS objects by Dale KG5QD's
WxSvr application.  UiView and other client applications must decode the
polygons and display them. 

http://home.earthlink.net/~kg5qd/APRS_Multiline_Protocol.html contains an
example of the encoded polygon format:

SPCSVR>APRS:;SPCS1528z*262100z3500.00NS07730.00WWSvr TStormWatch #174
}e0]FgcBS6:W{QFSAA

The polygon is described by:  }e0]FgcBS6:W

Problems began cropping up about a year ago.  Here is an example of the
present NWS Warning Polygon format:

LAT...LON 4137 10027 4035 10036 4035 10154 4066 10154
      4071 10121 4136 10120
TIME...MOT...LOC 0213Z 270DEG 17KT 4134 10064 4034 10141

The first and second lines list the points of the polygon in Decimal
degrees.  
The TIME...MOT...LOC is somewhat new AFAIK.  Apparently this shows the UTC
time, direction and speed of the warned object and 2 lat,lon pairs.

I suspect the problem we are observing is related to the parsing of the
LAT...LON pairs.  It is quite possible WxSvr is also parsing the
TIME...MOT...LOC fields as regular Lat,Lon pairs, resulting in a corrupted
polygon.  

I don't know if Dale is still actively supporting WxSvr, but it is an
awesome service to the APRS community.  While this error is annoying, we can
live with it.  I certainly hope Dale continues to provide us with such a
valuable service.  Thanks Dale.


Bill KC9XG  



>Stan/KC7EHJ
>





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