[aprssig] Balloon DFing on APRS (test lines)

[Lynn W. Deffenbaugh (Mr)]

I just double-checked my parser in APRSISCE/32 and I ONLY look for 
BRG/NRQ after a CSE/SPD Data Extension.  I'm not sure why, but that's 
the way I did it so far.  As for the interpretation and rendering of 
BRG/NRQ, here's my approach.

Of course the BRG is a decimal degrees that will govern the center of 
the wedge originating at the posit's coordinates.

N is just stored and displayed in the station information popup, but 
doesn't affect the rendering.
R is the range which I treat as a power of 2 in miles.  0 = 1, 1 = 2, 
out to 9=512 miles
Q is a quality which governs the degree width of the wedge according to 
the following table:

0 = No quality, no display
1 = 240 degrees (Bob didn't define)
2 = 120 degrees (saw a bug here, I had this at 60) (Bob said 45)
3 = 64 degrees (Bob said 22)
4 = 32 degrees (Bob said 11)
5 = 16 degrees (Bob said 6)
6 = 8 degrees (Bob said 3)
7 = 4 degrees (Bob said 2)
8 = 2 degrees (Bob said "Perfect", but I don't think there'd ever be 
perfect)
9 = 1 degree (Bob didn't include this?)

I did this rendering of the wedge (+/- half the degrees on either side 
of bearing) after considering of the range being based on powers of two 
and after discussion with several fox-hunters about how they actually do 
it and what kind of estimating accuracy they would be able to do.  Their 
conclusion was that precision isn't real good when you're out there 
waving a directional antenna trying to resolve the "strongest" signal, 
hence the scale above.

If we're going to specify it, I'd specify as a decreasing power of two 
(9-spec) as something that people can work out in the field or just poke 
in an estimate.  People have a better chance at remembering 1, 2, 4, 8, 
16, 32, 64 than Undefined,Perfect,2,3,6,11,22 IMHO.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

PS.  Here's the raw C code that I came up with over a year ago when I 
did this work based on the specs and discussions at the time:

if (FromDec(&s[1], 3, &v))
     Info->BRGNRQ.bearing = (short) v;
Info->BRGNRQ.number = s[5]-'0';
Info->BRGNRQ.range = 1<<(s[6]-'0');
Info->BRGNRQ.quality = s[7]-'0';
if (Info->BRGNRQ.quality)    /* 0 is 0 */
{    if (Info->BRGNRQ.quality == 1)
         Info->BRGNRQ.quality = 240;
     else if (Info->BRGNRQ.quality == 2)
         Info->BRGNRQ.quality = 60;
     else Info->BRGNRQ.quality = 1<<(9-Info->BRGNRQ.quality);
}


On 3/2/2012 12:00 PM, Bob Bruninga wrote:
>> I'm not really familiar with DF activities.
>> Can you dummy up a set of reports and send it to me
>> so I know what sort of thing to expect?
> OK I just put 3 DF reports on the map.  WB4APR-3, DF2 and DF3.
>
> They all have approximate lengths of about 500 miles and intersect out over
> the ocean.  Hopefully people with clients that plot DF's will see them.
>
> Notice the NRQ value is 997.  N is no longer used (so make it 9).  Then
> Range value of 9 means about 512 miles LENGTH of the bearing line.  The 7 is
> a quality factor.  8 would be a perfect bearing line.  7 is less precise on
> down.  A value of 2 would mean your bearing is within 45 degrees.  3 would
> mean 22 degrees, 4 wouild mean 11 deg, 5 is 6 deg, 6 is 3 deg, 7 is 2 deg
> and 8 is 1 deg.  Tho those are not formally defined.
>
> In the original APRSdos I could not do colored wedges, so I just made the
> dottedness of the line represent the quality of the bearing.  For modern
> programmers, a nice shaded transparent wedge with variable width would be
> real nice.
>
> The RANGE I do not ask my users to enter, but I generate that from the RANGE
> SCALE of the map they are using when they enter the DF object.  If they are
> zooomed into the to 2 mile range scale map when they add the object to the
> map, then the length of the line is 2 miles.  If they are zoomed out to the
> 512 mile range scale and add a DF line (as I have done), then the RANGE
> digit is the max of 9, indicating it is 512 miles long.
>
> So I guess working backwards.... on the RANGE digit,
>
> 9 = 512
> 8 = 256
> 7 = 128
> 6 = 64
> 5 = 32
> 4 = 16
> 3 = 8
> 2 = 4
> 1 = 2
>
> I just noticed that the APRS spec does not seem to go into this detail,
> unless I missed it...
>
> Bob, Wb4APR
>
>
>
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