Comments on: Unscientific GPS note

By: balrog

balrog — Wed, 21 May 2008 15:29:19 +0000

I didn’t have a chance to use the GTA02 much yet, but I didn’t notice it being worse than GTA01 on a cold start. On GTA02 every start is cold in the normal setup, though. I noticed it took very very long to see a first satellite at the very first start, after unpacking. It was similar with GTA01 I think.

I was also planning to get an external antenna, but I’m not going to get three to make a similar test.

By: Joseph

Joseph — Mon, 19 May 2008 14:07:45 +0000

Thanks for posting up the results of your test, I was just about to do the same thing myself before I noticed you’d already done it!

How do you find the FreeRunner’s satellite acquisition speed? Mine seems to take much longer to get a fix than on my gta01, although I’m pleased with the results once it finally happens.

I tried to purchase a selection of GPS antennas for testing a couple of weeks ago, but there seems to have been a communication error with our supplier. I’ll try and order some more and produce a blog post of results.

Cheers, Joseph

By: Anonymous Coward

Anonymous Coward — Mon, 28 Apr 2008 20:15:24 +0000

Speaking of accuracy, is there any way to get at the raw GPS data (time of flight basically) from any of the three devices? (That would be required for a software DGPS implementation to work.)

By: balrog

balrog — Mon, 28 Apr 2008 19:58:45 +0000

C. M.: Turns out orange is the GTA01, green GTA02 and blue N810, however the randomness on this image is because this is a cold-start for all three devices and just after the first fix when they’re allowed to be wrong, so it would be unfair to judge from this image. The initial small part of the way is inside a building also.

quatrox: true, but even in a bag they should all three see the same set of satellites and be able to make the same judgements. Also the kind of error that results from extrapolation will be more or less consistent across the different traces ( - when using the same GPS - so the real solution would be to always have a full bag of different devices with you and average over that).

I should probably try with an external antenna. Has someone used the Neo’s with external GPS antennas?

By: quatrox

quatrox — Mon, 28 Apr 2008 11:05:45 +0000

It is a nice test.

To get accurate data for OSM or similar, you need to do this test many times (on different time of the day) and then use the average.

Also, the GPS signal is not very strong, so having the devices in a bag is not really a good idea.

By: C.M

C.M — Mon, 28 Apr 2008 07:12:00 +0000

Nice test, but what color is what device on that map? I guess from the text that the N810 is the orange line, but which is GTA01? :-)