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i-Blue GM-2 USB GPS Receiver
OneRVer
Well I drove around the country side using my bluetooth, 4800, rate 1,,,, GM-2, 9600, rate 2 and GM-2, 115200, rate 5, maybe a hour on each. I really did not noticed any difference.

Is there something exactly you want me to look for?
tcassidy
Not really. It is all about how it feels to you unless there is something obviously different when you change the refresh rate. Possibly CoPilot ignores it.

Terry
MrUmbra
I calibrated my barometric ski altimeter against two nearby benchmarks. It indicates my GPS measuring point is 1400 feet AMSL so I used that height as a reference.

Here's a plot of about ten hours of fix altitude data. My GM-2 receiver was operating at one fix/second and sending at 115200 baud. WAAS was set off.

Average differential from 1400 feet for this run was about +12.4 feet. Reported altitude from the fix when I saved the screen was 1409 feet.

Also, I briefly tried plotting at five fixes/second rate and didn't note any difference in general performance.

I'll characterize altitude from my BU-353 next. It's going to appear radically different!

--- CHAS
Attached Images
alt_gm2.jpg  
MrUmbra
Here's altitude history from my BU-353. Data was collected from the same location I used for the GM-2.

--- CHAS
Attached Images
alt_bu353.jpg  
OneRVer
MrUmbra, On the scan with the gm-2, how long where you set on 5 repeats per seconds and have you noticed any difference by adjusting the baud rate?

By the way,,,,,excellent work.
MrUmbra
Quote:
Originally Posted by OneRVer
MrUmbra, On the scan with the gm-2, how long where you set on 5 repeats per seconds and have you noticed any difference by adjusting the baud rate?

By the way,,,,,excellent work.

Out of the box, my GM-2 sends at 115200 baud and I never have tried it otherwise; I use my receivers mainly with my own software.

I just ran 5 fixes/sec for about an hour .. just needed to test the software and, after reading through the comments, was curious if there would be an immediate noticeable difference. I noted none.

After Thanksgiving when I return home I'll run it for a day to see what happens. It requires a lot of time to collect data with so many possible configurations. As a minimum, data should be collected to include a sunrise and a sunset.

It's well understood that altitude from GPS doesn't work as well as horizontal positioning. At best, the error is about 1.5 times worse. That's because no satellites appear below you; obviously the earth gets in the way.

I believe there is some post processing going on in the GM-2. I didn't expect horizontal positioning to be as good as recorded in the plot I provided earlier. The horizontal scatter plot for the BU-353 is more in line with my observations for receivers I've tested. I notice upon initialization it locks the Course over Ground to some random value and holds it until the receiver begins moving. Someone on the GPSPassion forum mentioned Static Navigation which is an attempt stabilize velocity and direction when the receiver is stationary.

--- CHAS
Marvin Hlavac
Static Navigation crossed my mind this morning, too, when I compared your test results of BU-353 and GM-2. I plugged in my GM-2, launched S&T, and started to move in a slow speed. However, the location icon tracked the movement of my vehicle, even while I was starting to move very slowly, at bellow 5 KM/h or 3 miles per hour, so I suspect SN is not the reason GM-2 did so well in your tests.
Ken in Regina
Marvin, it may well be doing static navigation but just have a lower threshold for what it decides is "movement".

...ken...
etd083
Has anyone used the i-Blue GM-2 USB GPS receiver with the Linux operating system? I have a Linux laptop running Ubuntu and I am considering purchasing this receiver. Thanks.
BillLee
Given that the specs say

"NMEA Message NMEA0183 v3.1 baud rate 4800/9600/14400/19200/38400/57600, default 115200
Selectable Output: GGA, GLL,GSA, GSV, RMC, and VTG"

then, yes, gpsd will handle it. YMMV

Bill
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