[FOSS-GPS] introduction and first help request

[John Morris]

I'm also in the process of setting up a low cost base station.

The components I'm using:
  o Magellan AC12 gps card (~$160)
  o Ubuiquiti routerstation pro, single board computer (~$90)
  o FTDI USB-TTL converter cable (~$20)
  o Misc connectors, breadboard  (~$25)
  o Weathertight box, pipe fittings for antenna mount  (~$30)
  o Trimble compact dome antenna, ebay ($75)

The AC12 is a single frequency OEM card which has been around for a few
years. It is a 1 HZ unit, but it provides excellent phase measurements (even
better than the LEA-4T).  It requires a small amount of breadboarding to
hook  up, but it is mainly a matter of matching the wires from the USB-TTL
cable to the ribbon cable from the AC12. 

The "work in progress" software generates RTCM 3.1 records and distributes
them through a lightweight NTRIP caster, all of which run on the single
board computer. The Routerstation PRO is designed to be  wifi router, but it
has more than enough capacity. 

The entire station fits in a weathertight box; both data and power are
provided over a single Ethernet cable.



-----Original Message-----
From: foss-gps-bounces at lists.osgeo.org
[mailto:foss-gps-bounces at lists.osgeo.org] On Behalf Of Eugenio Realini
Sent: Wednesday, May 26, 2010 7:47 PM
To: Open Source GPS-related discussion and support
Subject: Re: [FOSS-GPS] introduction and first help request

Hi Mauro,

2010/5/27 Mauro Ugarte A <mauro.ugarte at cefop.udec.cl>:
> 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).

I checked here http://www.igs-ip.net/home and it seems that CONZ station
data can be accessed via NTRIP:

IP: www.igs-ip.net
Port: 2101
User & pass: you have to register here
http://igs.bkg.bund.de/ntrip/registeruser

This is the source table line for CONZ:

STR;CONZ0;Concepcion-TIGO;RTCM
3.0;1004(1),1006(15),1008(15),1012(1),1019,1020,1033(15);2;GPS+GLO;IGS;CHL;-
36.84;286.98;0;0;LEICA
GRX1200GGPRO;none;B;N;3600;BKG

It already has all the messages you could want, and if it is not located
where you need it to be, at least you can use it for some initial testing!

> 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?

That is right, you can do it either ways: buy a module with RTCM output or
construct RTCM once you got raw data. Obviously the second option requires
much more work and trial&error.

> 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.

Do you really need 10Hz for pedestrian rovers? If you mean for broadcasting
RTCM, permanent stations I know about broadcast at 1 Hz.
As for firmware bugs, they can happen with everything... let's hope u-blox
people learned from 5T mistakes and that 6T will be better ;)

Interesting project, anyway! Please keep us updated.

Eugenio
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