Thursday, April 28, 2016

The Gumstix Pi Pre-GO Project Chapter 4: Tennis Anyone?

I went to find the survey marker from and discovered that it was directly under a bridge.  It's also in the middle of a road.  I think that the coordinates they're publishing are not as accurate as I would like.  Strangely, there does not appear to be any more markers in the near vicinity of the office.  In the absence of an accurately located marker, I'm going to try and measure the dimensions of a tennis court with GPS data.   
So far, I have been very impressed with the Pre-GO PPP's performance.  I took it out for another field trip recently and had very nice 0-8 cm diameter groupings.  HDOP has been consistently near and below 1.0.  Geodetic engineers and surveyors would be pleased as punch.
I intend  to define the outer bounds of the court and the service lines within.  If I draw a 11x24m box with an 8.2x13m box smack in the middle, the test will be a success.  These measurements are based on the regulation court dimensions outlined in the image to the right.  I'm also considering measuring the accuracy of the altitude measurement.  The net is 1.6m high and if I can get that measurement from the base of the net post to the top, that will be an interesting data point as well.
The difficulty I have faced with my setup has not been the hardware itself.  This has performed perfectly throughout my experiments.  The issue has been with logging and interpreting the data.  I have been using my cellphone as an ad-hoc network router to ssh in to my Pi and during one experiment, the connection between my laptop and my GPS rig kept dropping out.  As a patchwork solution to this issue, I have added a physical connection to the RPi's system console: Just a short USB microB-to-A I can connect to with an extender cable.  If the WiFi drops out, I can just plug in.

Added to this is the fact that, in general, GPS modules spit data out once per second.  The Pre-GO PPP is no exception which means that, for a 1-hour test, there are 3600+ records to process. I'm using Python to interpret and plot the data but it still takes time.
Up next: RESULTS!

Monday, April 4, 2016

Pre-GO PPP and the Gumstix BBB Rover Cape

This is not going to be a long post.  Basically, I got the Pre-GO PPP working with the BeagleBone Black almost effortlessly through the Gumstix BBB Rover cape.  Rover was designed to be a remote-controlled robotics cape with dual PWMs for motor control on either side of the board, WiFi and Bluetooth connectivity and a whole lot of GPIO.  Conveniently enough, it has the 5-pin GPS header module on-board as well.

I downloaded the custom Yocto image, loaded it on to an SD card and fired it up.  Right away, I was able to see the raw GPS feed over a serial connection to UART04 but the image I had lacked the GPSD client tools.  After I disabled the IP-over-USB service and the BeagleBone's Ethernet controller and my router stopped arguing, I apt-got the tools and monitored the GPS data for a while.

It's confirmed, the Pre-GO PPP works great with the BBB Rover cape.

Meanwhile, I've completed my final test for the RPCM + Pre-GO PPP and am in the midst of analyzing the data.  I'll be posting my findings soon...