[Xastir] Compressed objects creep a little after creation?

[Tapio Sokura]

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