what is the units of extrinsic parameters?

[simpzan]

Hi, there. I am trying to run test-surround-view with following extrinsic parameters, it doesn't work. the parameters are calculated with opencv solvePnP(). what is the expected unit/format for the extrinsic parameters? and how to obtain them? Thanks!

#Position x
-0.03677052527289915;
#Position y
0.8791858435421135;
#Position z
0.08443662467164369
#Rotation x (roll)
-0.9773921430544583
#Rotation x (pitch)
0.02197753813021769
#Rotation x (yaw)
0.06278809969454573

[zongwave]

hi, the units of positions is in millimeters, rotations is in degrees Please refer to this page to understand how to get extrinsic parameters of a fisheye camera. https://sites.google.com/site/scarabotix/ocamcalib-toolbox

Thanks, Zong Wei

[simpzan]

@zongwave seems like Export Data only export intrinsic parameters. so I need to modify the matlab code to export the RRfin to get the extrinsic parameters, right?

[zongwave]

this tool export extrinsic parameters RRfin in terms of rotation matrix , you should convert the matrix into Euler angles roll/pitch/yaw

https://sites.google.com/site/scarabotix/ocamcalib-toolbox

RRfin

Contains the extrinsic parameters of every checkerboard with the respect to the camera reference frame. RRfin is a 3x3xM matrix, where M correspond to the respective image number. The first two columns of RRfin identify the ROTATION matrix (which is given by the column vectors Rx and Ry; Rz can be obtained as cross product between Rx and Ry). The third column of RRfin identifies the TRANSLATION vector of the checkerboard (i.e. [tx;ty;tz])

[simpzan]

@zongwave I just get the following RRfin matrix.

   0.008067090116959  -0.001721306462260  -0.598260206191614
   0.002777823138339   0.009548147942833  -1.367026172935751
   0.005215913693398  -0.002422803113083  -3.522215947851525

according to the doc,

• Rx is the first column, namely (0.008067090116959, 0.002777823138339, 0.005215913693398)
• and Ry is the second column, namely (-0.001721306462260, 0.009548147942833, -0.002422803113083),
• and Rz = Rx cross product Ry, namely (-0.00005653243414877, 0.00001056678510185, 0.00008180725482393).

now Rx, Ry, Rz vectors are all known, how to get the rotation matrix? I just googled a bit, the Rx is matrix of following form, not a vector. so I am still confused.

         | 1  0       0     |
    Rx = | 0  cos A  -sin A |
         | 0  sin A   cos A |

[zongwave]

RRfin defines a rotation 3-vector, matlab function "rodrigues" can be used to calculate corresponding rotation matrix. details of rodrigues rotation formula at wiki: https://en.wikipedia.org/wiki/Rodrigues%27_rotation_formula

rodrigues Transform rotation matrix into rotation vector and viceversa.

    Sintax:  [OUT]=rodrigues(IN)
    If IN is a 3x3 rotation matrix then OUT is the
    corresponding 3x1 rotation vector
    if IN is a rotation 3-vector then OUT is the 
    corresponding 3x3 rotation matrix

[liss1810]

this tool export extrinsic parameters RRfin in terms of rotation matrix , you should convert the matrix into Euler angles roll/pitch/yaw

https://sites.google.com/site/scarabotix/ocamcalib-toolbox RRfin Contains the extrinsic parameters of every checkerboard with the respect to the camera reference frame. RRfin is a 3x3xM matrix, where M correspond to the respective image number. The first two columns of RRfin identify the ROTATION matrix (which is given by the column vectors Rx and Ry; Rz can be obtained as cross product between Rx and Ry). The third column of RRfin identifies the TRANSLATION vector of the checkerboard (i.e. [tx;ty;tz])

Hi, @zongwave , extrinsic parameters of a fisheye camera means the position and Euler angles of a fisheye camera in world(vehicle) reference frame?

[wangqiang624731186]

@zongwave I just get the following RRfin matrix.

   0.008067090116959  -0.001721306462260  -0.598260206191614
   0.002777823138339   0.009548147942833  -1.367026172935751
   0.005215913693398  -0.002422803113083  -3.522215947851525

according to the doc,

* Rx is the first column, namely `(0.008067090116959, 0.002777823138339, 0.005215913693398)`

* and Ry is the second column, namely `(-0.001721306462260, 0.009548147942833, -0.002422803113083)`,

* and Rz = Rx cross product Ry, namely `(-0.00005653243414877, 0.00001056678510185, 0.00008180725482393)`.

now Rx, Ry, Rz vectors are all known, how to get the rotation matrix? I just googled a bit, the Rx is matrix of following form, not a vector. so I am still confused.

         | 1  0       0     |
    Rx = | 0  cos A  -sin A |
         | 0  sin A   cos A |

Have you solved the problem yet?

[wangqiang624731186]

@simpzan Have you solved the problem yet?

[shreshtashetty]

This might be a bit late, but just in case anyone working with libxcam moving forward has this doubt, following is the confirmation I've got from the OCamCalib forums:

The affine transform RRfin is [x y t]. Thus, to create a rotation matrix of RRfin for frame/image f do the following:

x = RRfin(1,:,frame);
y = RRfin(2,:,frame);
T = RRfin(3,:,frame);
z = cross(x,y);

R = [x y z]

And then with the R just created, the euler angles can be got as follows (in python3 code):

from scipy.spatial.transform import Rotation

r = Rotation.from_matrix(R)
angles = r.as_euler("zyx", degrees=True)

I hope this is right. If not, I hope the people maintaining this repo correct me.

[sandeshchand87]

hi, the units of positions is in millimeters, rotations is in degrees Please refer to this page to understand how to get extrinsic parameters of a fisheye camera. https://sites.google.com/site/scarabotix/ocamcalib-toolbox

Thanks, Zong Wei

This link is not available. It is not cleared to extract the extrinsic parameters from ocamcalib tool.