SITL: Add support for AirSim Simulator

[rajat2004]

Connector for AirSim based on the ArduCopter Solo API in AirSim: microsoft/AirSim#1387
Described properly with some relevant links in #11324
A WIP, need to figure out some connection issues.

Review Requested @tridge @peterbarker

[rajat2004]

@OXINARF Thanks!

The connection problem is described in detail here - microsoft/AirSim#1965
Briefly - Ardupilot is binding the sockets correctly and Airsim is also connecting to the sockets. Airsim is attempting to send the data but the SITL isn't receiving anything

[tridge]

@rajat2004 I've cleaned up the commits using an interactive rebase to follow our commit style
See http://ardupilot.org/dev/docs/submitting-patches-back-to-master.html

[rajat2004]

@tridge I thought that I would squash up the commits after the connection problems were fixed, but thanks for doing that

[rajat2004]

@lucasdemarchi Sorry, pressed the resolved button by mistake. If possible, could you open it again
The conversion from little-endian was something which I added after seeing a similar thing in SIM_JSBSim

ardupilot/libraries/SITL/SIM_JSBSim.cpp

Line 391 in 869a369

JSBSim sends in little-endian

Even I thought that using little-endian wouldn't be much of a problem, but added that just for making sure.
Should I remove the function?

Also, I didn't understand what you meant by fdm_packet should be a pod. What's a pod actually?

[rajat2004]

Fixed the connection issues.
Please note that this is in no way functional right now, the SITL isn't even initialising properly. Just that Airsim & Ardupilot are able to communicate
I'll add a readme also for how to build AirSim and use this Ardupilot connector and address the remaining review comments

[rajat2004]

Readme added

[rajat2004]

Fixed the gyro initialization by using EKF 10. The bad values are probably due to the collision of the drone with the ground in the beginning. Still figuring out the GPS problem

[peterbarker]

On Tue, 21 May 2019, Rajat Singhal wrote: + for(int i=0; i<kArduCopterRotorControlCount; ++i) { Should this be added to the style-guide?

Probably :-)

[rajat2004]

Made some changes, now it doesn't get the random GPS location. But still, there's no sat fix. It's not even detecting the GPS as u-blox which is displayed in the Mavproxy console. Any idea on what is causing this?
The GPS sent by the simulator is consistent (cause the drone won't take off)

I haven't squashed this commit so that it would be easier to review these changes and rewind if required

[rajat2004]

Also seeing Time has wrapped messages now. Probably due to incorrect use of the timestamp field.
Or because of the horrible timing between Ardupilot & Airsim right now?

[rajat2004]

Yeah, so the problem is with the timestamp, AirSim sends time from 1970 rather than the simulator start

[rajat2004]

Did a bit of hack(similar to the older JSBSim timing), but it's working!!
Getting the GPS lock also, able to arm
While trying to takeoff, the rotors are spinning but it doesn't move, it detects it as crash and then disarms.

But still, progress!
I'll push the changes in a few mins after a bit of cleanup

[rajat2004]

Added the sensor conversion changes.
Also added the params file, @tridge Thanks a lot for that!
Right now it's the full list, will change it to only those which have been modified
Readme has also been updated

[rajat2004]

This PR is no longer compatible with the ArduCopterSoloAPI in Airsim, instead, the corresponding Airsim branch is https://github.com/rajat2004/AirSim/tree/pr-arducopter.
All further development will be done on this branch

The earlier Airsim Solo compatible branch is here - https://github.com/rajat2004/ardupilot/tree/airsim-soloapi

Readme has been updated for using the Arducopter vehicle

[rajat2004]

JSON sensor packet parsing has been added, corresponding changes have been made to the Airsim branch

[rajat2004]

@peterbarker @tridge @khancyr @lucasdemarchi Could you do a fresh review of the PR as it currently stands? All the points raised till now have been addressed

[tridge]

nice work! This is ready to merge when it passes CI

[rajat2004]

@tridge Thanks!
Should we wait for the AirSim PR to get merged first? (however, that might take a long time, and merging this will make it easier to setup and for other developers to work on top of this)

Just wanted to confirm once

[tridge]

@rajat2004 no, we should merge here first I think. done!
I know you will be adding more features, but that can be done in a followup PR

[rajat2004]

Follow-up PR for adding Lidar is here - #11835
Also, #11821 is a PR for fixing ArduPilot build on MacOS

Please have a look at the above PRs and review