Digital Finds

Improved GPS: Resources and Notes

Theory:

We'll start with chapter six of the "Essentials of Satellite Navigation", describing improving GPS performance:

http://www.u-blox.com/customersupport/docs/GPS_Compendium(GPS-X-02007).pdf

We'll want A-GPS and DGPS; A-GPS greatly reduces the Time To First Fix (TTFF) and DGPS improves accuracy. With these we will enable field staff to take their phone out of their pocket, bring it out of suspend mode, and quickly enable accurate GPS recording.

Both A-GPS and DGPS rely upon assistance servers that communicate to the phones over TCP over WiFi/bluetooth/GPRS. We can establish servers either in fixed locations (office roofs) or semi-fixed locations (site specific).

Technical details:

• Michael Shiloh provides details of the u-blox chip found in the FreeRunner:

  http://gettingstartedopenmoko.wordpress.com/2008/05/28/openmoko-u-blox-usage/

• U-blox provided documentation (including how to get an A-GPS account):

  http://blogs.thehumanjourney.net/finds/resource/AssistNow-Online-Docu.zip

• Implementing A-GPS server and client (also found in the above zip):

  http://people.openmoko.org/matt_hsu/ImplementationAssistNowServerAndClient(GPS.G4-SW-05017-C).pdf

• C code for A-GPS:

  http://svn.openmoko.org/developers/matt_hsu/agps-online/

• Script to run the above application:

  http://lists.openmoko.org/pipermail/community/2008-June/018682.html

• GPRS will be needed:

  http://blogs.thehumanjourney.net/finds/entry/5

• There may be an issue using an external antenna?:

  http://lists.openmoko.org/pipermail/hardware/2008-May/000119.html

• The GTA01 had the GPS antenna orientated out of the top of the case - the FreeRunner is the same. Also raises the possibility of fixing another antenna connector (N Male, for example) to the FreeRunner via a Hirose U.FL pigtail:

  http://wiki.openmoko.org/wiki/Image:Gta01b_v3_case_top_open_pcb_lifted.jpg
  

Other:

• Not exactly improving GPS performance, but I tied a GTA01 to my mountain bike:

  http://blogs.thehumanjourney.net/finds/entry/20080306

• Measuring continental drift with GPS:

  http://news.bbc.co.uk/1/hi/england/nottinghamshire/2956026.stm

  (Included because I love the way it says that the GPS hardware is worth about £20,000; surely it should say that it costs about £20,000)

• "Unscientific GPS note" (thanks Esben):

  http://unadventure.wordpress.com/2008/04/28/unscientific-gps-note/

• Finally, I might be having a paper published on the topic of GPS measurement of peoples engagement with a city. Need to do some work on that though...
  

Posted at 12:24PM Jun 17, 2008 by Joseph Reeves in OLPA  |  Comments[3]