将colmap空三导入blender

主要问题是姿态系统的转换

经实验发现：

外参

colmap的外参四元数计算得到的R为Rc2w，即相机到世界的R。
Tx，Ty，Tz是原点在相机坐标系下的坐标，即P=[R|t]中的t
相机原点在世界系下的坐标为：C = -Rw2c·t
其中Rw2c=Rc2w的转置或逆

内参

blender不支持skew参数

焦距f = len/senor_size_max_width_or_heght*max(heiht,width)
主点由shift_x和shift_y表达

注意

colmap使用的cv系，对应的图像坐标系统为x向右，y向下。
blender实验的cg系，对应的图像坐标系统为x向右，y向上。
因此，旋转矩阵需要乘以一个变化矩阵，即：

        R_bcam2cv = Matrix(
        ((1, 0,  0),
        (0, -1, 0),
        (0, 0, -1)))

实验

        R_bcam2cv = Matrix(
        ((1, 0,  0),
        (0, -1, 0),
        (0, 0, -1)))
        print(R_bcam2cv)
        
        
        quat_a = mathutils.Quaternion((0.979036, 0.0658575 ,-0.189701 ,0.0341345))
        
        location = Vector((3.62986 ,0.228074 ,-0.737925))
        rotation = quat_a.to_matrix()
        location = -1*rotation.transposed() @ location
        rotation = rotation.transposed() @ R_bcam2cv
        print(location)
        
        instricstr = "2 2 3072 2048 2777.04 2756.82 1536 1024 "
        exstric = "1 0.973498 0.0553783 -0.21697 0.0464699 4.51543 0.363207 1.23276 "
        
        instric = instricstr.split()

        instrics = np.array(instric)
        instrics = instrics.astype(np.float)
        instric = instrics
        
        print(instric)
        
        #cam.dof_object = empty

        #scene.render.resolution_percentage = scale * 100


        # create a new camera
        bpy.ops.object.add(
        type='CAMERA',
        location=location)
        ob = bpy.context.object
        ob.name = 'CamFrom3x4PObj'
        cam = ob.data
        
        
        cam.name = 'CamFrom3x4P'
        cam.type = 'PERSP'
        #cam.lens = instric[4]/instric[2]*2.
        #cam.lens_unit = 'MILLIMETERS'
        cam.sensor_width  = 2
        sensor_width_in_mm = cam.sensor_width

        sensor_fit = 'AUTO'
        get_sensor_fit(sensor_fit, instric[2], instric[3])
        cam.sensor_fit = 'HORIZONTAL'
        
        print(cam.sensor_fit)
        
        #cam.shift_x = 0
        #cam.shift_y = 0
        cam.clip_start = 1.0
        cam.clip_end = 250000000.0

        w   = instric[2]
        h   = instric[3]
        f_x = instric[4]
        f_y = instric[5]
        c_x = instric[6]
        c_y = instric[7]

        cam.shift_x = -(c_x / w - 0.5)
        cam.shift_y = (c_y - 0.5 * h) / w

        cam.lens = f_x / w * sensor_width_in_mm

        pixel_aspect = f_y / f_x
        
        scene = bpy.context.scene
        scale = 1
        scene.render.resolution_x = float(instric[2]) / scale
        scene.render.resolution_y = instric[3] / scale
        
        scene.render.pixel_aspect_x = 1.0
        scene.render.pixel_aspect_y = pixel_aspect



        ob.matrix_world = Matrix.Translation(location)@(rotation.to_4x4())
        
        location, rotation = scene.camera.matrix_world.decompose()[0:2]
        print(location,rotation)

原始影像与渲染影像：

参考：
https://docs.blender.org/api/current/bpy.types.Camera.html
https://github.com/zju3dv/pvnet-rendering/blob/master/blender/blender_utils.py
https://www.rojtberg.net/1601/from-blender-to-opencv-camera-and-back/