IMU units for acceleration? about rpg_dvs_ros HOT 5 CLOSED

I see line 628 of https://github.com/uzh-rpg/rpg_dvs_ros/blob/master/davis_ros_driver/src/driver.cpp should convert from caer g units to m/s^2 unit. (I don't know what the switch is there for, since caer should deliver the IMU data in same form for each type of DAVIS).

                       if (davis_info_.chipID == DAVIS_CHIP_DAVIS346B)
                        {
                            // convert from g's to m/s^2 and align axes with camera frame
                            msg.linear_acceleration.x = -caerIMU6EventGetAccelY(event) * STANDARD_GRAVITY;
                            msg.linear_acceleration.y = -caerIMU6EventGetAccelX(event) * STANDARD_GRAVITY;
                            msg.linear_acceleration.z = -caerIMU6EventGetAccelZ(event) * STANDARD_GRAVITY;
                            // convert from deg/s to rad/s and align axes with camera frame
                            msg.angular_velocity.x = -caerIMU6EventGetGyroY(event) / 180.0 * M_PI;
                            msg.angular_velocity.y = -caerIMU6EventGetGyroX(event) / 180.0 * M_PI;
                            msg.angular_velocity.z = -caerIMU6EventGetGyroZ(event) / 180.0 * M_PI;
                        }
                        else
                        {
                            // convert from g's to m/s^2 and align axes with camera frame
                            msg.linear_acceleration.x = -caerIMU6EventGetAccelX(event) * STANDARD_GRAVITY;
                            msg.linear_acceleration.y = caerIMU6EventGetAccelY(event) * STANDARD_GRAVITY;
                            msg.linear_acceleration.z = -caerIMU6EventGetAccelZ(event) * STANDARD_GRAVITY;
                            // convert from deg/s to rad/s and align axes with camera frame
                            msg.angular_velocity.x = -caerIMU6EventGetGyroX(event) / 180.0 * M_PI;
                            msg.angular_velocity.y = caerIMU6EventGetGyroY(event) / 180.0 * M_PI;
                            msg.angular_velocity.z = -caerIMU6EventGetGyroZ(event) / 180.0 * M_PI;
                        }

Line 112 of https://github.com/uzh-rpg/rpg_dvs_ros/blob/master/davis_ros_driver/include/davis_ros_driver/driver.h defines
`
static constexpr double STANDARD_GRAVITY = 9.81;

`

https://github.com/inilabs/libcaer/blob/master/include/events/imu6.h defines cAER units for acceleration as g's. Therefore I think that the g units of cAER are being multiplied by another factor of g in this code, rather than being divided by it. I must be missing something.

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Thanks for pointing this out. I think the switch is now obsolete. This code was there to fix an earlier version of libcaer regarding the DAVIS346B.
7e741c2

It seems that libcaer has been fixed in the time since that commit, making sure that the IMU for the DAVIS346B has the same notation as the one for the DAVIS240C, and we did not notice. We did not fix it since we always compute the camera-to-IMU transformation (rotation and translation) using Kalibr.
We will remove this now obsolete switch. @eliasm @supitalp just be aware.

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Fixed in PR #59

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Thanks Guillermo, and reading the code I now I see I was mistaken. A 1g acceleration from cAER is correctly multiplied by 9.8m/s^2 to result in a final 9.8m/s^2 ROS value.
It still doesn't explain why I'm getting wrong values in my jAER rosbag acceleration, but it is probably something in that RosBagFileInputStream class, not here.

Have you validating physical correctness of the acceleration values by application using rpg-dvs code?

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Hi Tobi. We have validated the physical correctness of the acceleration values for the DAVIS240C sensors. In case of the mini DAVIS346B, we have reported to iniLabs that the values given by the accelerometer are off by some amount, and so, we have to calibrate the IMU (while at rest) and compensate for this offset whenever we use our visual-inertial odometry algorithms.

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