[FOSS-GPS] rtklib: simple DGPS post-processing experiment

Fri Jul 23 13:08:06 EDT 2010

Dear Timo

> 1) Is it normal that neo1-neo2.pos has 1380 points while both neo1.pos
> and neo2.pos have over 7200 points?
> 2) Did this really improve anything? ;-) Since the number of points is
> different I am not quite sure how to interpret the scatter plots.

No.

Most of solutions are rejected by validation because of large noises.
Add -x 2 options and see warning in *.trace file.

To output full solutions, you have to tune error parameters
according to your environment but RNX2RTKP 2.3.0 can
not tune error parameters. Try RTKPOST or RNX2RTKP 2.4.0
released soon.

Large multipath might much degrades solutions. I recommend
you had better use good antennas.

regards,

Tomoji TAKASU
WWW: http://gpspp.sakura.ne.jp

--------------------------------------------------
From: "Timo Juhani Lindfors" <timo.lindfors at iki.fi>
Sent: Friday, July 23, 2010 12:16 AM
To: <foss-gps at lists.osgeo.org>
Cc: <ttaka at yk.rim.or.jp>
Subject: [FOSS-GPS] rtklib: simple DGPS post-processing experiment

> Hello Tomoji,
>
> as promised, here's a report of my attempts to use rtklib for
> post-processing.
>
> Hardware setup
> ==============
>
> 1) neo1 is an openmoko gta02V5.
> 2) neo2 is an openmoko gta02V7.
> 3) Both devices are outside on a wooden table.
> 4) The LCD of each device faces downwards.
> 5) The "up" direction of each device points to South-East.
> 6) Distance between the devices is one meter (give or take a few
> centimeters).
> 7) neo2 is North-East of neo1.
>
> Captured data
> =============
>
> http://iki.fi/lindi/gps/experiment/1/neo1.ubx
> http://iki.fi/lindi/gps/experiment/1/neo2.ubx
>
> Post-processing steps
> =====================
>
> $ rtklib-convbin neo1.ubx
> $ rtklib-convbin neo2.ubx
> $ rtklib-rnx2rtkp -p 1 -l 60.217480929 24.393206102 71.2617 neo1.obs 
> neo2.obs neo1.nav > neo1-neo2.pos
> $ head -n20 neo1-neo2.pos
> % program   : rnx2rtkp ver.2.3.0
> % inp file  : neo1.obs
> % inp file  : neo2.obs
> % inp file  : neo2.nav
> % obs start : 2010/07/22 06:25:13.0 GPST (week1593 368713.0s)
> % obs end   : 2010/07/22 08:29:45.0 GPST (week1593 376185.0s)
> % ref pos   : 60.217480929   24.393206102    71.2617
> %
> % (lat/lon/height=WGS84/ellipsoidal,Q=1:fix,2:float,4:dgps,5:single,ns=# 
> of satellites)
> %  GPST                  latitude(deg) longitude(deg)  height(m)   Q  ns 
> sdn(m)   sde(m)   sdu(m)  sdne(m)  sdeu(m)  sdun(m) age(s)  ratio
> 2010/07/22 06:29:01.998   60.217692722   24.393138007    61.6161   4   4 
> 2.3673   0.9796   2.9740  -1.1745  -1.0261  -0.5434   0.00    0.0
> 2010/07/22 06:29:02.998   60.217716772   24.393110643    65.7936   4   4 
> 2.3680   0.9798   2.9741  -1.1751  -1.0262  -0.5407   0.00    0.0
> 2010/07/22 06:29:03.998   60.217727627   24.393090583    69.9502   4   4 
> 2.3688   0.9801   2.9742  -1.1758  -1.0263  -0.5379   0.00    0.0
> 2010/07/22 06:29:04.998   60.217727239   24.393083772    73.7900   4   4 
> 2.3695   0.9803   2.9744  -1.1764  -1.0265  -0.5352   0.00    0.0
> 2010/07/22 06:29:05.998   60.217700360   24.393116329    72.5172   4   4 
> 2.3702   0.9805   2.9745  -1.1770  -1.0266  -0.5324   0.00    0.0
> 2010/07/22 06:29:06.998   60.217646591   24.393137804    75.9859   4   4 
> 2.3709   0.9807   2.9747  -1.1776  -1.0267  -0.5296   0.00    0.0
> 2010/07/22 06:29:07.998   60.217605988   24.393149454    77.8729   4   4 
> 2.3717   0.9809   2.9748  -1.1783  -1.0269  -0.5268   0.00    0.0
> 2010/07/22 06:29:08.998   60.217573994   24.393164286    76.2576   4   4 
> 2.3724   0.9812   2.9750  -1.1789  -1.0270  -0.5240   0.00    0.0
> 2010/07/22 06:29:09.998   60.217562704   24.393172695    76.4654   4   4 
> 2.3731   0.9814   2.9751  -1.1795  -1.0271  -0.5212   0.00    0.0
> 2010/07/22 06:29:10.998   60.217558401   24.393176600    73.0197   4   4 
> 2.3738   0.9816   2.9752  -1.1802  -1.0272  -0.5183   0.00    0.0
>
> Evaluation
> ==========
>
> Scatter plots of neo1.pos, neo2.pos and neo1-neo2.pos are at
>
> http://lindi.iki.fi/lindi/gps/experiment/1/scatter.html
>
> Histograms of distance to average (simple sqrt((lat-lat_avg)**2 +
> (lon-lon_avg)**2)) are at
>
> http://lindi.iki.fi/lindi/gps/experiment/1/histo.html
>
> Open questions
> ==============
>
> 1) Is it normal that neo1-neo2.pos has 1380 points while both neo1.pos
> and neo2.pos have over 7200 points?
>
> 2) Did this really improve anything? ;-) Since the number of points is
> different I am not quite sure how to interpret the scatter plots.
>
> -Timo
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