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[DPRG] Further Quandries on GPS...
Subject: [DPRG] Further Quandries on GPS...
From: dpa
dpa at io.isem.smu.edu
Date: Wed Jan 2 09:55:23 CST 2008
Howdy,
Here's a plot of 40 minutes worth of wandering GPS locations recorded with
a handheld Garmin Etrex sitting in a fixed location:
<http://www.geology.smu.edu/~dpa-www//gps/gps_40min.png>
I need to convert the lat/lons to something that makes more sense
(i.e. feet or meters) but you can see that it doesn't drift anything
like what Kenneth is getting.
Kip wrote:
> The first thing I would try is a bigger ground plane under the patch
> antenna. You should have a minimum of 40mm x 40mm, but anything bigger
> is better and it needs to be grounded to vehicle ground. Bigger should
> help reduce ground reflections.
I found I had to do this on jBot to get reasonable GPS data, and also
mount the GPS rather high above the rest of the robot platform. Here's
a picture:
<http://geology.heroy.smu.edu/~dpa-www/robo/Encoder/imu_odo/jbot_imu_odo_02.jpg>
that shows the GPS (yellow and black device) mounted in a grounded aluminium
channel which shields it on 3 sides, which is what I eventually had to do
to get a reasonable performance.
FYI, jBot continously calculates its position from odometry as well as GPS and
then calculates the difference between the two locations. In a typical 15 minute
run the two never drift more that 96 inches from each other, and are typically
in the 17 to 54 inch range. (I think 17 inches is the quanta of the smallest
measureable GPS increment with the handheld garmin).
HNY,
dpa
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