I have a Venus634LPx GPS on a breakout board from SparkFun.
The documentation is very cryptic, so I did not manage to configure it manually through the UART (although I can read data from it). Luckily, the SkyTraq GPS Viewer & Configuration program works under wine (I'm on LinuxMint):
I still can't figure out what the pinning parameters mean. The closest thing to an explanation I found online is in a thread from 2009:
In many applications, the position and/or velocity is represented as point on a display. To make that point appear more visually stable and/or accurate to the end user, position pinning is implemented. In position pinning the reported position will not change unless some user-defined criteria are met.
The criteria can be set in pinning parameters.
Another website, where they use GPS to build a time server (similar to my own application), says:
This is what I did to configure my module:
- Enabled position pinning
- Disabled all NMEA strings except for GGA, GSA, GLL and ZDA
- Set update rate to 1Hz and output sync to UTC
- Set baud rate to 9600 (higher is not better!)
Application Note AN0003 from SkyTraq only gives the following relevant information:
What do these parameters mean? Is any better documentation available?
Answer
I sent an email to SkyTraq, and they replied by sending me Application Note AN0025 v5 (Uploaded with permission).
There is a slight difference from the datasheet in how this note names the parameters:
- Pinning speed
PSPEED
inkm/h
- Pinning threshold
PTH
ins
(pinning cnt
in datasheet) - Unpinning speed
UPSPEED
inkm/h
- Unpinning threshold
UPTH
ins
(unpinning cnt
in datasheet) - Unpinning distance
UPDISTANCE
inm
When the speed is below PSPEED
for longer than duration PTH
, it enters a "position pinned state", where the GPS module is considered stationary. The reported location will not move around at all, contrary to the normal behaviour where the location jumps around in a stochastic fashion.
If there is a 3D
fix, it will return to the normal "unpinned" state when the speed exceeds UPSPEED
for longer than UPTH
. If the fix is only 2D
or intermittent, it takes longer (see pp.4–5). In either case, if the position of the GPS module has drifted by more than UPDISTANCE
, it will also "unpin".
The application note says nothing about the purpose of this feature. I have an unconfirmed suspicion that pinning the location might improve the GPS time estimate on stationary devices.
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