Airsim: Getting Acceleration

Created on 26 Sep 2017 · 6Comments · Source: microsoft/AirSim

Is there an API call to get the drone's acceleration? I'd like something like the getVelocity() function in RpcLibClient.hpp

The main reason I want this is because I'd like to populate ROS IMU messages. I can populate the velocity and orientation fields myself, but not the acceleration fields.

Source

hngenc

Most helpful comment

Hey @sytelus ,
are there any news regarding sensor API's? I could not find a specific issue for that yet.

Fab7c4 on 4 Mar 2018

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All 6 comments

Maybe I can help you if you provide more information:

Which acceleration do you want? Ground truth from the physics engine or simulated estimations from the IMU?
What is your setup? Software in the loop or hardware in the loop?

Ricardus312 on 27 Sep 2017

Thanks for your response, @Ricardus312!

I'd like simulated estimations from the IMU.
I can use either SITL or HITL, although I'd prefer a solution that works with the simple_flight_controller.

hngenc on 27 Sep 2017

Well, it seems we both have the same problem (https://github.com/Microsoft/AirSim/issues/476). I haven't figured out how to get the acceleration from the IMU yet, but I think I am pretty close from it. I will share with you all what I have discovered until now, maybe it could be useful for you:

SitL setup (Simple Flight). On simple flight, if you press 'R' button during simulation, it starts to record flight images and writing a log file (in Windows, it saves to UserDocumentsAirSimThisDate). That log file outputs the position and orientation of the drone, sampling several times per second, and you can modify easily the code of the log function to make it output velocities and accelerations, both linear and angular. Here is how to get velocities and accelerations (ground truth) in simple flight:
- Go to the directory of your Unreal project (usually at DocumentsUnreal ProjectsProject_name in Windows, but if you are using the default Blocks environment that comes with AirSim, it could be on AirSimUnrealEnvironmentsBlocks)
- Open the 'Project.sln' file with Visual Studio (e.g. if you are using the default blocks environment, the file is Blocks.sln).
- On the solutions explorator, navigate to GamesProjectPluginsAirSimSourceRecordingRecordingFile.cpp" and open it (other option is going directly to the directory "..Project_namePluginsAirSimSourceRecording" and open with Visual Studio the file "RecordingFile.cpp".
- About line 50 of that file, you will see this code:
  line.append(std::to_string(timestamp_millis)).append("t")
  .append(std::to_string(kinematics.pose.position.x())).append("t")
  .append(std::to_string(kinematics.pose.position.y())).append("t")
  .append(std::to_string(kinematics.pose.position.z())).append("t")
  .append(std::to_string(kinematics.pose.orientation.w())).append("t")
  .append(std::to_string(kinematics.pose.orientation.x())).append("t")
  .append(std::to_string(kinematics.pose.orientation.y())).append("t")
  .append(std::to_string(kinematics.pose.orientation.z())).append("t")
  
  All you have to do is add to that code these lines, and you will get all the velocities and accelerations (ground truth):
  .append(std::to_string(kinematics.twist.linear.x())).append("t")
  .append(std::to_string(kinematics.twist.linear.y())).append("t")
  .append(std::to_string(kinematics.twist.linear.z())).append("t")
  .append(std::to_string(kinematics.twist.angular.x())).append("t")
  .append(std::to_string(kinematics.twist.angular.y())).append("t")
  .append(std::to_string(kinematics.twist.angular.z())).append("t")
  .append(std::to_string(kinematics.accelerations.linear.x())).append("t")
  .append(std::to_string(kinematics.accelerations.linear.y())).append("t")
  .append(std::to_string(kinematics.accelerations.linear.z())).append("t")
  .append(std::to_string(kinematics.accelerations.angular.x())).append("t")
  .append(std::to_string(kinematics.accelerations.angular.y())).append("t")
  .append(std::to_string(kinematics.accelerations.angular.z())).append("t")
- Also, if you don't want to get the screen captures, you only have to replace (or comment) the line 21 of that file:
  imageSavedOk = FFileHelper::SaveArrayToFile(image_data, *filePath);
  For this other one:
  imageSavedOk = true;
- Regarding the IMU accelerations, if you read the paper
  (https://github.com/Microsoft/AirSim/blob/master/docs/paper/main.pdf), in the point 3.4 it says that
  
  "AirSim offers sensor models for accelerometer, gyroscope, barometer, magnetometer
  and GPS. All our sensor models are implemented as C++ header-only library and
  can be independently used outside of AirSim"
So in theory, it is possible to write a code that just imports the IMU sensor, calls a method and gets

the angular velocities and accelerations from it. Unfortunately, I am not a C++ programmer (yet) and

my understanding of the code is very limited, so I still haven't been able to do this by myself. The code

for the sensors is at "..Project_namePluginsAirSimSourceAirLibincludesensors". Check out the

code in "..imuImuSimple.hpp". I think that somebody with good C++ skills could easily modify the

code in "RecordingFile.cpp" to call the IMU ang get its outputs, but I still haven't that "good C++

skills".

For the Hardware int the Loop setting, theoretically it is possible to get the MavLink messages between your external flight controller hardware and the simulator using an external program called Px4LogViewer, look at the docs (https://github.com/Microsoft/AirSim/blob/master/docs/px4_logging.md).