More information about camera focal lengths and offsets of the principal point

Hi Holger,

Could you please provide the details about the camera which was used for capturing the Nuscenes data. I need focal lengths and offsets of the principal point from the top-left corner of the image frame.

And also, I would like to understand how the calibrated_sensor (rotation and translation) data is captured.

Thanks,
Lakshmi

Hi. That’s exactly what the calibrated sensor table is about (see https://github.com/nutonomy/nuscenes-devkit/blob/master/schema.md). Rotation and translation are the extrinsics. camera_intrinsic is the intrinsics for the camera. From these you can retrieve focal lengths and principal point.
For the calibration procedure, see https://www.nuscenes.org/data-collection.

Hi Holger,
I calculate that the focal length is about 8.9mm. Is that right?
for exmaple: 1266/[sqrt(1600^2+1200^2)/(25.4/1.8)]

What are the numbers? Image resolution is 1600x900.
The lens is F1.8 f5.5mm 1/1.8".

1266 come from a camera_intrinsic,original image resolution is 1600x1200(uncropped), 1 in = 25.4mm

Thank you for your reply

You are right about the image resolution.
Take a look at https://github.com/nutonomy/nuscenes-devkit/issues/185.
The poster there references this image: https://www.vision-doctor.com/images/stories/kamera/grundlagen/camera_sensor_sizes.png
The diagonal of 9mm (close to 8.9mm) corresponds to “7.2mm x 5.4mm” (close to 5.5).
Perhaps your formula computes the diagonal?

OK,I see, Thanks.:grin::grin: