Searching for USB GPS

[marholt]

I'm looking for USB gps, that has accurate data for the altitude and position.
I tested from Columbus V-800 +. The test was performed on octokopter with a autopilot. On the drone, there is also an internal GPS, which I've compared columbus to. In addition, I also mounted my phone and logged the data using sport tacker application. Columbus has a very poor results (see attached graph blue line.) The red line on graph is a programmed route of which would be ideal, but the actual route is green line. Even when I comparede with the phone, the information on an internal GPS and on the phone very similar.
I've also contacted columbus why is there so much differences betwen the  data, but there was no answer from them.

I don't want to use the internal GPS because of 2 reasons:
It has communication via the CAN bus and it's own protocol, for which there is no documentation, and I do not know if decoded it correctly, because sometimes I get false information.
If I'm connected to CAN bus with non standart equipment for the drone, I can't guarantee that this will not interfere with the autopilot. (Problem with insurance if the drone crashes)

So I'm looking for a suitable USB gps, where there is sufficiently accurate data for altitude. If it also includes air preasure correction for altitude measurement, even better.
 It may also be on the RS232 bus.
Does anyone have any suggestions?

[dave_k]

Have you looked at any of the modules from uBlox?

[matkar]

It seems like the Columbus GPS has data averaging... What is the time scale on your chart?
I wouldn't worry about CAN interference too much since you only read the data. It seems you figured out the protocol correctly. Could those occasional glitches you mention not come from misreading CAN but erroneous altitude measurements? You can further configure your CAN reader in "listen only" mode so it doesn't interfere with CAN at all.
What kind of CAN reader do you have?

[marholt]

For CAN reading and decoding I'm using bealgebone. It is possible that beaglebone causes those glitches.
So I can buy a new CAN reader and stil wonder if I decoded the protocol correctly or buy a new GPS.