Convert CV2 extrinsic to Blender camera.object.location and camera.object.rotation_euler parameters

extrinsic_to_blender.py

import math
import cv2
import numpy as np


def isRotationMatrix(R):
    Rt = np.transpose(R)
    shouldBeIdentity = np.dot(Rt, R)
    I = np.identity(3, dtype=R.dtype)
    n = np.linalg.norm(I - shouldBeIdentity)
    return n < 1e-6


# Calculates rotation matrix to euler angles
# The result is the same as MATLAB except the order
# of the euler angles ( x and z are swapped ).
def rotationMatrixToEulerAngles(R):

    assert isRotationMatrix(R)

    sy = math.sqrt(R[0, 0] * R[0, 0] + R[1, 0] * R[1, 0])

    singular = sy < 1e-6

    if not singular:
        x = math.atan2(R[2, 1], R[2, 2])
        y = math.atan2(-R[2, 0], sy)
        z = math.atan2(R[1, 0], R[0, 0])
    else:
        x = math.atan2(-R[1, 2], R[1, 1])
        y = math.atan2(-R[2, 0], sy)
        z = 0

    return np.array([x, y, z])


def extrinsic_to_blender(rotation, translation):
    adjustment_mat = np.array([[1, 0, 0], [0, -1, 0], [0, 0, -1]])
    rotataion_matrix, _ = cv2.Rodrigues(rotation)
    blender_camera_location = -rotataion_matrix.T @ translation
    blender_camera_rotation = rotationMatrixToEulerAngles(
        rotataion_matrix.T @ adjustment_mat
    )
    return blender_camera_rotation, blender_camera_location