Increased data accuracy - Garmin GPS V - an experiment

[itchytweed]

People climb Mt. Everest because it was there. Myself, getting out the extra decimals from my GPS V was to relieve a bit of creational boredom and to really see what my unit was capable of.

 

First off, I used Antoinio's software available at http://artico.lma.fi.upm.es/numerico/miembros/antonio/async/

 

I went and made some modifications to the two packages, async and gar2rnx, to run on my copy of Linux and its hardware. The software is running on an IBM T41 laptop.

 

I went and did a 45 minute occupation of a site that is listed with the NGS and is part of the Wisconsin High Accuracy Reference Network that is near my office.. I can guarantee that this is a totally non-scientific test and can't be used for geodetic work. I had mounted the GPS V stick antenna on a PVC pipe 5 feet above the benchmark. The GPS V head was located in my vehicle running off of a 12 volt battery and 30 feet of 9913 coax between the antenna and the GPSr. My laptop used async to grab all the data from the GPSr over the serial link. I ended up occupying the site for 45 minutes. Also, I had the GPSr running for 3 days straight to get the unit's temperature stabilized and the crystal settled down.

 

I crunched the data through gar2rnx and ended up gettting a rinex file after using option -etrex. I would have loved to stay there longer than I did but there were other pending issues that had to be taken care of.

 

At home, I scoured the web to find out if there was a public site that post-processed L1-only RINEX files. That came up a dry hole. But, I did find this site: http://mywebpages.comcast.net/dmilbert/softs/. Dennis wrote a L1-only post processor in FORTRAN. I used the ddpr1 program. I had to work on that to get the program to compile and run under f77. I grabbed the necessary files to feed it (ephemeris and rinex for a local CORS site). When it was done crunching, I converted the X,Y and Z values into Lat Lon Height. Height was way off but Lat and Lon was within 0.5 meter.

 

I can't complain a bit about the result using plain antenna that picks up everything, the cars multipath from the nearby road, consumer-grade equipment,etc. The setup was a hack but it was a proof of concept that worked. Now only if I had access to a choke ring antenna and four hours of free time...

 

Dear Santa, I have been a good boy this year. Can I get a complete dual-receiver Thales ProMark3 with all the goodies in my stocking this year?

[+apersson850]

What did you then use the decimals for?

[itchytweed]

What did you then use the decimals for?

The GPSr only display five decimals. I am getting out 8 decimals with the software. The GPSr is capable of more decimals but they are not needed for what I am trying to do. Plus, I know that the hardware can't supply a stable enough accuracy to use all the decimals.

 

This is all in the name of fun.