question about calibration file

[amiltonwong]

Dear all,

Take example as Desk Sequence (png file and bag file) for testing. For png images, the focal length and principle setting and distortion setting in file cameraCalibration.cfg is: 0.771557 1.368560 0.552779 0.444056 1.156010 640 480 0.771557 1.368560 0.552779 0.444056 1.156010 640 480 That means: fx=0.771557, fy=1.368560, cx= 0.552779,cy=0.444056, distortion param = 1.156010

While for /camera_info within LSD_room.bag file are: K[0]: 254.326954 K[1]: 0 K[2]: 267.381897 K[3]: 0 K[4]: 375.934381 K[5]: 231.599091 K[6], K[7]: 0 K[8]: 1 That means: fx=254.326954, fy=375.934381, cx= 267.381897,cy= 231.599091 and also D is found to be 0.

Why are these two K settings(Camera matrix) so different significantly?

Hope someone can hint me for this question.

THX~ Milton

[budhi15]

My guess is that they used separate cameras?

[hiankun]

Also, the values in cameraCalibration.cfg might have been devided by camera width and height.

[amiltonwong]

@budhi15, Maybe. But I choose the same image source (which I extract from LSD_room.bag file) and apply them in two approaches, two results are almost the same: [1] rosbag play /root/Downloads/LSD-SLAM/Desk_Sequence/LSD_room.bag rosrun lsd_slam_core live_slam image:=/image_raw camera_info:=/camera_info

or

[2](I extract the images frame into /root/images from LSD_room.bag) rosrun lsd_slam_core dataset _files:=/root/images _hz:=0 _calib:=/root/Downloads/LSD-SLAM/Desk_Sequence/LSD_room/cameraCalibration.cfg

So , these two K settings(Camera matrix) which differ significantly may have some relation between themselves, but I can't figure out the conversion formula between them. As suggest from @hiankun, still I cannot find the exact conversion formula.

Hopefully someone could point me to the answer :)

Thanks a lot~

[aggarwal-himanshu]

I guess its in atan model. But still the values dont match

[xslittlegrass]

I did a similar test and the parameters seem to match for me.

The "camera_info" topic of LSD_room.bag has the following message:

header: 
  seq: 2743
  stamp: 
    secs: 1400002262
    nsecs: 209756768
  frame_id: /camera
height: 480
width: 640
distortion_model: ''
D: [0.0, 0.0, 0.0, 0.0, 0.0]
K: [254.32695388793945, 0.0, 267.38189697265625, 0.0, 375.93438148498535, 231.59909057617188, 0.0, 0.0, 1.0]
R: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
P: [254.32695388793945, 0.0, 267.38189697265625, 0.0, 0.0, 375.93438148498535, 231.59909057617188, 0.0, 0.0, 0.0, 1.0, 0.0]
binning_x: 0
binning_y: 0
roi: 
  x_offset: 0
  y_offset: 0
  height: 0
  width: 0
  do_rectify: False

This means

fx=254.326954
fy=375.934381
cx= 267.381897
cy= 231.599091
width = 640 
height = 480 

and the distortion parameters are all zero.

Since the images are already rectified, we can use the calibration format corresponding to the pre-rectified images, which has the format

fx/width fy/height cx/width cy/height 0
width height
none
width height

This means the calibration parameters are:

0.397386 0.783197 0.417784 0.482498 0
640 480
none
640 480

I use these parameters and it works well with the extracted image from the LSD_room.bag file

rosrun lsd_slam_core dataset _files:=/Downloads/LSD_room_bag/images _hz:=0 _calib:=/Downloads/LSD_room_bag/calib.cfg