Python Opencv SolvePnP 产生错误的翻译向量

Question

我正在尝试使用同形异义词校准并找到Blender 3d中单个虚拟摄像机的位置和旋转。我正在使用Blender，这样我就可以在进入更困难的现实世界之前仔细检查我的结果。

我在固定相机的视图中渲染了十张棋盘在不同位置和旋转的图片。使用OpenCV的Python，我使用cv2.calibrateCamera从十张图像中检测到的棋盘角中找到内在矩阵，然后在cv2.solvePnP中使用它来查找外在参数（平移和旋转）。

然而，尽管估计的参数接近实际参数，但仍有一些可疑的事情发生。我对翻译的初步估计是(-0.11205481,-0.0490256,8.13892491).实际位置(0,0,8.07105)。很接近吧？

但是，当我稍微移动和旋转相机并重新渲染图像时，估计的平移变得更远了。 估计： (-0.15933154,0.13367286,9.34058867) .实际： (-1.7918,-1.51073,9.76597) .Z 值接近，但 X 和 Y 不接近。

我完全糊涂了。如果有人能帮我解决这个问题，我将不胜感激。以下是代码（它基于 OpenCV 提供的 Python2 校准示例）：

#imports left out
USAGE = '''
USAGE: calib.py [--save <filename>] [--debug <output path>] [--square_size] [<image mask>]
'''   
args, img_mask = getopt.getopt(sys.argv[1:], '', ['save=', 'debug=', 'square_size='])
args = dict(args)
try: img_mask = img_mask[0]
except: img_mask = '../cpp/0*.png'
img_names = glob(img_mask)
debug_dir = args.get('--debug')
square_size = float(args.get('--square_size', 1.0))
pattern_size = (5, 8)
pattern_points = np.zeros( (np.prod(pattern_size), 3), np.float32 )
pattern_points[:,:2] = np.indices(pattern_size).T.reshape(-1, 2)
pattern_points *= square_size
obj_points = []
img_points = []
h, w = 0, 0
count = 0
for fn in img_names:
    print 'processing %s...' % fn,
    img = cv2.imread(fn, 0)
    h, w = img.shape[:2]
    found, corners = cv2.findChessboardCorners(img, pattern_size)        
    if found:
        if count == 0:
            #corners first is a list of the image points for just the first image.
            #This is the image I know the object points for and use in solvePnP
            corners_first =  []
            for val in corners:
                corners_first.append(val[0])                
            np_corners_first = np.asarray(corners_first,np.float64)                
        count+=1
        term = ( cv2.TERM_CRITERIA_EPS + cv2.TERM_CRITERIA_COUNT, 30, 0.1 )
        cv2.cornerSubPix(img, corners, (5, 5), (-1, -1), term)
    if debug_dir:
        vis = cv2.cvtColor(img, cv2.COLOR_GRAY2BGR)
        cv2.drawChessboardCorners(vis, pattern_size, corners, found)
        path, name, ext = splitfn(fn)
        cv2.imwrite('%s/%s_chess.bmp' % (debug_dir, name), vis)
    if not found:
        print 'chessboard not found'
        continue
    img_points.append(corners.reshape(-1, 2))
    obj_points.append(pattern_points)        
    print 'ok'
rms, camera_matrix, dist_coefs, rvecs, tvecs = cv2.calibrateCamera(obj_points, img_points, (w, h))
print "RMS:", rms
print "camera matrix:n", camera_matrix
print "distortion coefficients: ", dist_coefs.ravel()    
cv2.destroyAllWindows()    
np_xyz = np.array(xyz,np.float64).T #xyz list is from file. Not shown here for brevity
camera_matrix2 = np.asarray(camera_matrix,np.float64)
np_dist_coefs = np.asarray(dist_coefs[:,:],np.float64)    
found,rvecs_new,tvecs_new = cv2.solvePnP(np_xyz, np_corners_first,camera_matrix2,np_dist_coefs)
np_rodrigues = np.asarray(rvecs_new[:,:],np.float64)
print np_rodrigues.shape
rot_matrix = cv2.Rodrigues(np_rodrigues)[0]
def rot_matrix_to_euler(R):
    y_rot = asin(R[2][0]) 
    x_rot = acos(R[2][2]/cos(y_rot))    
    z_rot = acos(R[0][0]/cos(y_rot))
    y_rot_angle = y_rot *(180/pi)
    x_rot_angle = x_rot *(180/pi)
    z_rot_angle = z_rot *(180/pi)        
    return x_rot_angle,y_rot_angle,z_rot_angle
print "Euler_rotation = ",rot_matrix_to_euler(rot_matrix)
print "Translation_Matrix = ", tvecs_new

Answer 1

我想你可能认为tvecs_new是相机位置。有点令人困惑的是，事实并非如此！事实上，它是世界原点在相机坐标中的位置。要在物体/世界坐标中获得相机姿势，我相信您需要

-np.matrix(rotation_matrix).T * np.matrix(tvecs_new)

您可以使用cv2.decomposeProjectionMatrix(P)[-1]获得欧拉角，其中P是[r|t] 3 x 4 外禀矩阵。

我发现这是一篇关于内在和外在的好文章......