[Gpsbabel-misc] gpsbabel for realtime tracking ...

[J. E. M. I. <je...@co...>]

I've got a simple near-realtime tracking system working for the most 
part.  thanks to gpsbabel, it's been easy (and fun!) to bridge the 
various pieces together ... GREAT JOB!  I have a couple questions that I 
hope you can help with.  my "tracker" consists of:

1. Garmin Rino 120, serial to USB converter cable, plugged into ...
2. Linux laptop (FC7), running ...
3. gpsbabel -T -i garmin -f /dev/ttyUSB0 -o kml,units=s -F <somefile> 
(version 1.3.4)
4. googleearth, with a Network Link to <somefile> refreshing every 2 seconds

gpsbabel puts out a point every second or so and pieces them together 
nicely in the kml file.  sweet!  however, if I try to use nmea input, 
points come much less frequenty.  I found this section of code that I 
think explains this while I'm stationary:

               nmea_parse_one_line(ibuf);
               if (lt != last_read_time && curr_waypt && trk_head) {
                        if (curr_waypt != last_waypt) {
                                nmea_add_wpt(curr_waypt, trk_head);
                                last_waypt = curr_waypt;
                        }
                        lt = last_read_time;
                }

I expect to get much faster nmea updates while I'm moving though.  not 
the case.  I'm lucky if I get a point every 60 seconds while driving 
around town.  with gpsd and gpspipe I get nmea sentences every 1-2 
seconds.  while I'm satisfied to get "garmin" input points for now, I 
thought I'd try to understand why the nmea input isn't doing what I 
expected.  any ideas?

the second gpsbabel feature I'm curious about is the kml output.  at 
least in realtime mode, the kml file I'm getting out has Position, 
Points and Path elements.  the Points don't seem all that useful in 
realtime.  can that be turned off?  what I had in mind, or what seems 
reasonable to view "realtime" in GE anyway, is a Path with a single icon 
always at the head of the Path (ie, current Position), and have the GE 
3D viewer track (move with) this current Position.  with the gpsbabel 
1.3.4 options for kml output, it doesn't appear possible to get that.  
or is it?  if not, are there plans to offer more control over realtime 
kml output in the future?  or do you have any other suggestions?

finally, I've heard GE has a limit of around 5000 points in any single 
kml file.  can you confirm this?

I'm making a cross country trip next week and have cached alot of the 
imagery along the route in GE.  my setup should make the 1400 mile trip 
more interesting!

thank you,

Ed