v1.397: obtaining full-resolution GPS location (admin privileges necessary)
This discussion was created from comments split from: Interpreting the GPS data/status in the Admin console.
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The only thing I'd consider doing is adding a Kiwi server-side command you could run to dump the GPS location. That way you'd have to use ssh from any non-Kiwi machine to get to it.
Sample command from a Linux host: The contents of info.json will be like: Process with your favorite JSON format processor.
Glenn n6gn
Axes represent on the order of 1m in latitude and 2m in longitude and in spite of antenna position on NW corner of house and entirely shielded by it this small amount of positional error is all I see after a few ten's of minutes warmup in the Kiwi:
With help from G3ZIL it is now clear that the apparent high precision of the GPS data was due to the Kalman filter. Additional "step change" tests were performed whereby I moved the kiwi/GPS about 20m between two points along a line of longitude and nearly N/S. I did this twice, once with the Kalman filter switched on and another time with it off. For each test the system was given time to stabilize prior to start of test.
The general results seem to be much less noisy with filter ON but having the step/impulse response of a narrow bandwidth filter as should be expected. This filter, like any similar filter, has group delay. This means that rapid changes don't propagate through it quickly and in order to get good data one must wait.
With the filter switched OFF the data is very noisy. This is what the filter takes out. Standard deviation was on the order of 7m in longitude and in this case 50 or more samples need to be taken to get within the ~1m range.
For my portable/active-antenna/GPS/kiwi/battery measurement system and John's administrative access method, taking this many data points requires many minutes.
I think the summary may be that while the internal GPS can eventually give good data, this data must be filtered either by the Kalman filter or otherwise in order to achieve precision. It appears that the time required for this may be significantly longer than for other GPS receivers.
If your kiwi/GPS is stationary, has good satellite coverage and tracking you may be able to achieve pretty good location accuracy, however if you are moving it be prepared to process the data and wait a while if you want precision.
At least that's how it looks at this point.
I've a couple FrSky GPS modules which are using their own S-BUS comms but there are many others specifically for RC flight use with Android/Linux (see Ardupilot).
I think they might be NMEA format (don't quote me).
I've just ordered a couple of USB GPS dongles as I wanted one for other HAM timing use.
If standard serial (E.G. USB) GPS was an option there is nothing to stop someone tailoring the GPS cost, bands and location to the application.
I don't mean to be negative by the way, looking to improve GPS while moving is great for a few users but probably more work than taking external data(?).
Since at the moment I'm trying to use a portable kiwi to understand near-field noise source characteristics I think Google maps with the above method may be just fine.
The GPS in the Kiwi is an economical way to provide time/frequency data and serves that purpose well. Fine-grained surveying really isn't in the requirements list. I really was only updating my previous report as a caution in case others might try to push performance past what seemed possible because of my first report.