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.
Hi everyone,
I have a similar question. I’m new to this topic so maybe this is a stupid one. Sorry in advance if this is the case.
If I don’t get it wrong, the focal length that is obtainable from the intrinsic matrix is expressed in pixels. How do I transform it into millimeters? if the sensor size is 7.2mm x 5.4mm as you reported, and the original image size is 1600 x 1200. Does it mean that a pixel is exactly 7.2/1600 x 5.4/1200 = 0.0045 x 0.0045 mm? thus, the focal length is for instance 1260*0.0045 = 5.67mm ?
