[aprssig] Is floating point telemetry allowed in APRS?

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Thu Mar 28 13:08:18 CDT 2013


On 3/28/2013 11:58 AM, Robert Bruninga wrote:
> Actually, the original APRSdos can take decimals, but again, the limit is
> 3 FIXED bytes.  So you can have 0.1 up to 9.9, but beyond 10, you cannot
> use a decimal because it would make the field 4 bytes wide and violate the
> spec.  Same goes for SPEED field.

 From aprs101.pdf:

> There are five 8-bit unsigned analog data values (expressed as 3-digit
> decimal numbers in the range 000–255), followed by a single 8-bit digital
> data value (expressed as 8 bytes, each containing 1 or 0).

Seems pretty clearly specified to be 000 to 255 and 3 digits (a dot 
isn't a digit).

Speed isn't quite as specifically described, but the verbiage and 
example of 000/000 make it pretty clear that it's most likely intended 
to be 3 digit integers:

> The 7-byte CSE/SPD Data Extension can be used to represent the course and
> speed of a vehicle or APRS Object.
>
> The course is expressed in degrees (001-360), clockwise from due 
> north. The
> speed is expressed in knots. A slash / character separates the two.
>
> For example:
> 088/036 represents a course 88 degrees, traveling at 36 knots.
>
> If the course and speed are unknown or not relevant, they can be set to
> 000/000 or .../... or VVV/VVV.
>
> Note: In the special case of DF reports, a course of 000 means that the DF
> station is fixed. If the course is non-zero, the station is mobile.

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



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