support Acceleration and Angular Rate in the NMEA protocoll

[bomilkar]

Many OpenVarios contain IMU/MEMS. That is a 3 axis acceleration and 3 axis angular rate (aka Gyroscope) sensor.
I'm in the process to improve the Wind Calculation in XCSoar. Find the discussion here:
XCSoar/XCSoar#1449
Admittedly, this is a long standing issue, but I'm committed to take a new approach in the coming weeks.

The extensions to the NMEA protocol I'm looks like this:

$POV,A,-1.5099,-.0292,13.7134*18
$POV,G,4.165,-8.709,-10.479*1B

In essence:
Adding identifiers 'A' for Acceleration and 'G' for Gyro (aka Angular Rate)
The identifiers are followed by 3 values for X, Y and Z-axis.
Values are presented in body frame axis (X forward, Y right, Z down)
Acceleration in m/s²
Gyro in °/s (Degree per second).
It's assumed that the sensor inside the instrument is aligned and calibrated to these axis and units.

Here is an example of a left turn, together with other data for TEvario, StaticP, DynamicP:

$POV,A,-1.5144,-.1317,13.3568*1D
$POV,G,.010,6.854,-7.530*32
$POV,E,2.40,P,789.06,Q,432.07*17

Example of right turn:

$POV,A,-.7468,-.1626,10.0739*24
$POV,G,3.519,5.072,10.852*10
$POV,E,2.45,P,775.45,Q,480.27*1D

Sentences can be split across multiple lines or combined like this example:
$POV,A,-1.0378,-.0888,11.2615,G,-.982,-7.249,-12.905,E,3.48,P,778.01,Q,432.51*xx

I'm preparing PRs for XCSoar to support the counterpart to this protocol extension. It will come in several parts addressing infrastructure, OpenVario parser, new circling wind algorithm.

[linuxianer99]

Hey @bomilkar

Looks like a good improvement, as the hardware ist mostly on the sensorboard.
One question will be, if the code for read out the IMU is more related to sensord ?? Not to variod ...

Or do you have some special things in mind doing the issue in the variod project ?

[bomilkar]

Or do you have some special things in mind doing the issue in the variod project ?

You are right, the code to send the NMEA sentences should perhaps go to sensord.
However, I just wanted to define the protocol before we start coding.

FYI: I've just submitted PR XCSoar/XCSoar#2069 to lay the foundation inside XCSoar.
Once we agreed on the protocol I will submit a PR to parse it in XCSoar's device driver.

If you still feel this Issues should be some place else I'm happy to move it. Just let me know.

[linuxianer99]

I transfered to sensord :-)

Let me write the current protocol in a MD File in sensord repo. Then you can add your extension und do a PR.

Ok for you ?

[bomilkar]

I transfered to sensord :-)

Let me write the current protocol in a MD File in sensord repo. Then you can add your extension und do a PR.

Ok for you ?

Very well!
Many thanks.

[linuxianer99]

Here the current protocol.

@bomilkar Feel free to add your changes and provide them via Pull request ..

[bomilkar]

PR done
#49

[bomilkar]

It's time to extend sensord to support gyroscope and acceleration NMEA output.
XCsoar will support it's end in the upcoming release, 7.44 . It'll bring a big improvement in wind calculation. So it's worth the effort.

I'm more than happy to support that project, but I don't have the hardware to test it. In fact I would appreciate to get involved. I have some input to share to get the most out of it. Would somebody please step up and take the lead?