Re: Different location on APRSIS32 and APRS.fi
Mystery solved (I believe). Why didn't you TELL us you had POSITION AMBIGUITY enabled on the Kenwood? Here's the translation:toggle quoted messageShow quoted text
S x53 83. Lat 3 A=1
5 x35 53. Lat 5 B=0
Q x51 81. Lat 1 C=1
L x4c 76. Lat SPACE! - South
Z x5a 90. Lat SPACE! - +100 lon
L x4c 76. Lat SPACE! - East
So, we have 35 1b.bb (b=space) for position ambiguity to only 10s of minutes.
ABC=101 is In Service
And we've got South and +100 East
M x4d 77. -28 = 49 + 100 = 149 Degrees
4 x34 52. -28 = 24 Minutes
x1c 28. - 28 = 0 Hundredths
l x6c 108. - 28 = 80 *10 = 800 knots?
x20 32. - 28 = 4 /10 = 0 knots, 400 degrees?
x1c 28. - 28 = 0 = 00 degrees
K x4b 75. = Symbol
\ x5c 92. = Table
] x5d 93.
Further, if speed >=800, speed -= 800 or 0 knots
if course >=400, course -=400 or 0 heading
And we end up with 35 1b.bbS 149 24.00E 0 knots, 0 heading, \K symbol (Kenwood).
So, basically anything goes on the position because the ambiguity setting says we really don't know WHERE the station SHOULD be, but it should be somewhere around 10 minutes. So anything between 01 and 19 would be just as good a guess for the actual position.
aprs.fi has 35 15.00S 149 25.00E
aprsis32 has 35 10.00S 149 24.00E
aprs.fi seems to have interpreted the ambiguity in the center of where it might have been, but definitely seems to have missed the longitude by 1 degree. APRSIS32 truncated the ambiguity, so I'm actually going to add a ToDo list item to SHOW the ambiguity as described on http://www.aprs.org/symbols.html quoted below. Then at least we'd KNOW that we don't know WHERE the station actually is!
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
*Ambiguity Plots:* . Since not all positions in APRS are known to the same precision, a significant attribute of all APRS symbols is the provision to show the four ranges of ambiguity of 0.1, 1, 10 and 60 nautical miles. . Notice how the object named GUESSED above is not shown with a symbol, but with a circle. This is because this station is transmitting or entered with a 1/10th mile ambiguity with his position. The station's symbol does show up at large area scales, but once you zoom the map below the scale at which the size of the ambiguity is larger than the "size" of the symbol, then the symbol disappears so that there can be no missinterpretation by the person viewing that there is precision where there is not. These ranges of ambiguity are conveyed just like a written position is conveyed. If a position is only known to the nearest degree (60 nm), then only the degrees are sent. . If the position is only known to the nearest minute, then only the degrees and integer minutes are transmitted. . and So on down to Tenths of a minute. If all digits are known, then the position conveys the full precision inherent in APRS which is to the nearest 100th of a nautical mile or about 60 feet.
*Ambiguity in the Spec:* . There has been lots of confusion over Position Ambiguity caused by the poor wording in the spec that can be incorrectly interpreted as implying a truncation of digits and a lat/long box of ambiguity. . It is not a /truncation/ and it is not a box. . The position field in APRS is a string field, not a numeric field. . One should place in that field by /inclusion/ only the digits the sender wants the receiver to use. . Further the spec implies that this results in a box of ambiguity. . This is wrong. because it would imply vastly different sizes of inprecision at the equator and at the poles. . It is clear that the intent of position ambiguity was a range in nautical miles, since Ambiguity was defined in the LATITUDE field only, where the digits do correspond to Nautical Miles. . And they do give the same circular area everywhere on earth.
*Plotting Position Ambiguity:* . The recommended plot of position ambiguity is shown above for GUESSED. . That is, a circle with a radius of the ambiguity centered on the given position. (Not centered in a box of LAT/LONG) . Further, the symbol may be displayed as long as the size of the symbol is larger than the circle of ambiguity. But on higher resolution zooms, when the size of the circle becomes larger than the size of the symbol, then the symbol should NOT be displayed because it implies a location at the center which is incorrect. Only the circle should be displayed at these zooms. . Further, the "center" location of this circle should be slightly randomized (say within half the range of ambiguity) so that if there are many stations reporiting the same location and ambiguity, that all of their circles will show. . These circles are not intended to be precise sizes or edges of ambiguity, but simply a graphical representation to the viewer that these positions are not well known.
Lynn W. Deffenbaugh wrote:
aprs.fi has 35 15.00S 149 25.00E