Hi,
I just noticed that some compressed objects tend to creep a little in
location after being created in Xastir. Here's an example:
I created a non-moving compressed object (I left speed/course/altitude
fields blank) with a location of N 60 12.011, E 024 56.171. The first
location field of an APRS object that Xastir sent was '0&i#TiQK', which
converted back to readable form is about N 60 12.01115 and E 024 56.17185.
The second time that object is sent, the location field is '0&i#TiQH',
notice the change in the last character. The longitude in this packet is
about E 024 56.17091. And then the third time includes a location field
of '0&i#TiQE', a longitude of E 024 56.16996. All packets sent after the
third one until the object was killed contained the same location as the
third packet, '0&i#TiQE'. All of the kill packets also had '0&i#TiQE' as
the location.
In practice this creep is just barely noticeable if you zoom to level 1.
Converted to distance, the difference between the first and third packet
is about 2 meters.
Without looking at the code, I have a theory of a sequence of events
(hmm, I'm sounding like the narrator in Seconds from Disaster
tv-series..) that might exaplain this:
1) Xastir takes my input coordinates, converts them into Xastir's
internal representation and then to compressed format, and sends the object.
2) Xastir sees the APRS packet it just sent and converts the compressed
position into Xastir's representation of the location -> a slight change
can take place here.
3) When the time comes to resend an object, Xastir converts the internal
format location got from 2) above to compressed format again, moving the
object a little again.
4) goto 2), until the location settles into a value that doesn't cause a
step change when converting between Xastir's internal format and APRS
compressed format location.
I'm running CVS Xastir (1.8.5), compiled on November 4th.
Tapio
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