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Hello, I have two questions on D435i(or T265) IMU sensor output rate.
- I found that the accelerometer gives output rate of 62.5Hz, while the gyroscope gives output rate of 200Hz. Why are those different? Is it because the gyroscope output is not averaged by time, but the accelerometer output is averaged by a certain time to give output in 62.5Hz? I'd like to know how the IMU output is handled internally. (whether it is the raw output, or time-averaged)
- One more question, the T265 gives the estimated pose stream in 200Hz. If the accelerometer raw output is 62.5Hz, how the pose is calculated in 200Hz? Is it only propagating without accelerometer updates?
Your answer would be really appreciated.
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Intel have published a guide to getting data from the D435i and T265 (which both use the same IMU component).
https://www.intelrealsense.com/how-to-getting-imu-data-from-d435i-and-t265/
The guide states: "The D435i depth camera generates and transmits the gyro and accelerometer samples independently, as the inertial sensors exhibit different FPS rates (200 / 400Hz for gyro, 63 / 250Hz for accelerometer). Each IMU data packet is timestamped using the depth sensor hardware clock to allow temporal synchronization between gyro, accel and depth frames"
".The T265 tracking camera utilizes the same IMU sensor as the D435i. However, unlike the D435i, which delivers the raw IMU data directly to the host PC, the T265 redirects IMU readings into an Intel Movidius Myriad 2 Vision Processing Unit (VPU). The inertial sensor data is also complemented by video from two fisheye monochrome sensors that are fed into the VPU as well".
The guide also says about the 6DOF pose:
**********
Each sample contains:
– Position vector [xyz]
– Orientation quaternion [xyzw]
– Linear velocity and acceleration vectors
– Angular velocity and acceleration vectors
– Tracking confidence [hi/med/low]
It adds that pose is not available on D435i, and is hardware-generated at 262 Hz on T265.
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Intel have published a guide to getting data from the D435i and T265 (which both use the same IMU component).
https://www.intelrealsense.com/how-to-getting-imu-data-from-d435i-and-t265/
The guide states: "The D435i depth camera generates and transmits the gyro and accelerometer samples independently, as the inertial sensors exhibit different FPS rates (200 / 400Hz for gyro, 63 / 250Hz for accelerometer). Each IMU data packet is timestamped using the depth sensor hardware clock to allow temporal synchronization between gyro, accel and depth frames"
".The T265 tracking camera utilizes the same IMU sensor as the D435i. However, unlike the D435i, which delivers the raw IMU data directly to the host PC, the T265 redirects IMU readings into an Intel Movidius Myriad 2 Vision Processing Unit (VPU). The inertial sensor data is also complemented by video from two fisheye monochrome sensors that are fed into the VPU as well".
The guide also says about the 6DOF pose:
**********
Each sample contains:
– Position vector [xyz]
– Orientation quaternion [xyzw]
– Linear velocity and acceleration vectors
– Angular velocity and acceleration vectors
– Tracking confidence [hi/med/low]
It adds that pose is not available on D435i, and is hardware-generated at 262 Hz on T265.
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