[FOSS-GPS] introduction and first help request

[Mauro Ugarte A]

Hi to everyone,

  I'm Mauro Ugarte, electronic engineering student at Universidad de 
Concepción, Chile (spanish native speaker, so excuse my english). I'm 
working on my undergraduate thesis taking part of a new small research 
team whose objective is to develop a low cost system for real time 
relative precise positioning (at least 0.6 m relative to some fixed 
point, geodesic precission is always desirable but in our case not 
crucial or extremely needed) of pedestrian rovers (5-15 kph), on a small 
baseline (0 - 5 km), so discovering this mailing list almost makes me 
cry ;'-).
  As a start, we are going to follow some of the paths signaled here 
(rtklib, gogps), but we lack of two fundamental parts:

1- First of all, in Chile there is nothing like a GPS reference station 
network providing corrections on NRTK/NTRIP, which we could rely on. 
There is an IGS station, though. It is near our lab (about 3 km), 
codenamed CONZ and labeled "highrate_permanent" under GNSS/files > Data 
Archive > File Browser at GNSS Data Center website 
(http://igs.bkg.bund.de/index/index) and provides RINEX files that 
should help at post-processing but not for real time aplications (please 
correct me if i'm wrong).

2- Even when the excellent works aforementioned (rtklib, gogps) clearly 
stated which GPS module was used to conduct the research (primarily the 
u-blox LEA-4T), we noted that u-blox is getting that module out of the 
market (the entire xxx-4x line) so doing some futuristic thinking, we 
don't want to do all the research to rely on hardware with extinction 
deadline.

  So, considering the above, let me ask this:

1- Should we buy a RTK capable reference station module, that outputs 
RTCM-RTK messages to use them as an input to rtklib/gogps? (example: 
magellan DG-14), or could we use another low cost module that outputs 
raw data measurements and "convert" that raw data into the corresponding 
RTCM-RTK messages to feed rtklib/gogps?. I ask this because it seems to 
me that RTCM V3.1 messages broadcasted by RTK reference stations 
(1001-1002 for precision GPS L1 only, 1003-1004 for precision GPS L1 & 
L2) could be "constructed" by raw data output, and messages 1005-1006 
too, using the station position. Is all this possible or am i missing 
something?

2- Do you know alternatives to LEA-4T, at low cost, that seems to you 
that should stay around at least a couple of years and output raw data 
which we can feed (or convert to feed) to rtklib/gogps?. We know that 
there are the u-blox LEA-5T and LEA-6T, but those output raw data at 2 
Hz and 5 Hz respectively, and the last one is just born so firmware bugs 
could happen as they happened to LEA-5T, so if you know another faster 
and cheaper, please let me know.

  Finally, my gratitude for all the hard work done here.

Sincerely yours,

Mauro Ugarte A.
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