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Suppose I have got the face euler angles (pitch, yaw, roll). How can draw the 3D Coordinate Axes which show the face pose?

Here is an example from here:

enter image description here

David Buck
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tidy
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  • why not just take the code from your link ? – berak May 13 '15 at 06:48
  • I do not want to use OpenGL to draw the result. – tidy May 13 '15 at 06:52
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    Create the 3D axes as vertices/vectors. apply the rotation to them. project them to your camera/image plane – Micka May 13 '15 at 07:05
  • Thanks, @Micka. Would you please give me more details about your answer? Any code example or opensource reference for that? – tidy May 13 '15 at 07:42
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    no. read about camera model, computer graphics, rendering pipeline, camera projection. If you want the easy way, use OpenGL. If not, learn and understand how it is done (won't be too difficult for projecting just simple lines). - opencv has some functions to help you building up the camera model and transforming your vertices, but you will have to understand what you want to do and how to achieve it. - http://en.wikipedia.org/wiki/3D_projection – Micka May 13 '15 at 07:44
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    Do what @Micka suggested. If you do not want to use OpenGL, then what do you want? Do you want to use OpenCV? – bendervader May 20 '15 at 06:17
  • You are being picky about the solution, so you should explain what your parameters are. What tools are you open to using @HoneyTidy – OYRM May 21 '15 at 14:32
  • Yes, I want to use OpenCV to draw the result. – tidy May 22 '15 at 01:51
  • It is a standard technique to draw projected lines in OpenCV for visualizations. No opengl is necessary. – Andrzej Pronobis May 22 '15 at 07:02

5 Answers5

9

This can be done in pure OpenCV as long as you have your camera parameters. You should be able to create three vectors corresponding to axis x, y, z (basically points [0,0,0] [1, 0, 0], [0, 1, 0], [0, 0, 1] which you will later project into the image plane. You should first rotate those points according to your yaw/pitch/roll (e.g. by multiplying them by a rotation matrix).

In order to project 3D points to the image plane, use the projectPoints function. It takes 3D points, camera parameters and generates 2D image points. Once you have the image points, you can simply use the line function to draw lines between the projected central point ([0,0,0] in 3D) and each of the resulting projections of the axis points.

Andrzej Pronobis
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6

A simple example:

def draw_axis(img, R, t, K):
    # unit is mm
    rotV, _ = cv2.Rodrigues(R)
    points = np.float32([[100, 0, 0], [0, 100, 0], [0, 0, 100], [0, 0, 0]]).reshape(-1, 3)
    axisPoints, _ = cv2.projectPoints(points, rotV, t, K, (0, 0, 0, 0))
    img = cv2.line(img, tuple(axisPoints[3].ravel()), tuple(axisPoints[0].ravel()), (255,0,0), 3)
    img = cv2.line(img, tuple(axisPoints[3].ravel()), tuple(axisPoints[1].ravel()), (0,255,0), 3)
    img = cv2.line(img, tuple(axisPoints[3].ravel()), tuple(axisPoints[2].ravel()), (0,0,255), 3)
    return img

![]

3

I used thie code. It's from Basel Face model(BFM), you can find matlab code from their web sites


def draw_axis(img, yaw, pitch, roll, tdx=None, tdy=None, size = 100):

    pitch = pitch * np.pi / 180
    yaw = -(yaw * np.pi / 180)
    roll = roll * np.pi / 180

    if tdx != None and tdy != None:
        tdx = tdx
        tdy = tdy
    else:
        height, width = img.shape[:2]
        tdx = width / 2
        tdy = height / 2

    # X-Axis pointing to right. drawn in red
    x1 = size * (math.cos(yaw) * math.cos(roll)) + tdx
    y1 = size * (math.cos(pitch) * math.sin(roll) + math.cos(roll) * math.sin(pitch) * math.sin(yaw)) + tdy

    # Y-Axis | drawn in green
    #        v
    x2 = size * (-math.cos(yaw) * math.sin(roll)) + tdx
    y2 = size * (math.cos(pitch) * math.cos(roll) - math.sin(pitch) * math.sin(yaw) * math.sin(roll)) + tdy

    # Z-Axis (out of the screen) drawn in blue
    x3 = size * (math.sin(yaw)) + tdx
    y3 = size * (-math.cos(yaw) * math.sin(pitch)) + tdy

    cv2.line(img, (int(tdx), int(tdy)), (int(x1),int(y1)),(0,0,255),3)
    cv2.line(img, (int(tdx), int(tdy)), (int(x2),int(y2)),(0,255,0),3)
    cv2.line(img, (int(tdx), int(tdy)), (int(x3),int(y3)),(255,0,0),3)

    return img
Hong-jik Kim
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1

Some clarification of the code given above

def draw_axis(img, rotation_vec, t, K, scale=0.1, dist=None):
    """
    Draw a 6dof axis (XYZ -> RGB) in the given rotation and translation
    :param img - rgb numpy array
    :rotation_vec - euler rotations, numpy array of length 3,
                    use cv2.Rodrigues(R)[0] to convert from rotation matrix
    :t - 3d translation vector, in meters (dtype must be float)
    :K - intrinsic calibration matrix , 3x3
    :scale - factor to control the axis lengths
    :dist - optional distortion coefficients, numpy array of length 4. If None distortion is ignored.
    """
    img = img.astype(np.float32)
    dist = np.zeros(4, dtype=float) if dist is None else dist
    points = scale * np.float32([[1, 0, 0], [0, 1, 0], [0, 0, 1], [0, 0, 0]]).reshape(-1, 3)
    axis_points, _ = cv2.projectPoints(points, rotation_vec, t, K, dist)
    img = cv2.line(img, tuple(axis_points[3].ravel()), tuple(axis_points[0].ravel()), (255, 0, 0), 3)
    img = cv2.line(img, tuple(axis_points[3].ravel()), tuple(axis_points[1].ravel()), (0, 255, 0), 3)
    img = cv2.line(img, tuple(axis_points[3].ravel()), tuple(axis_points[2].ravel()), (0, 0, 255), 3)
    return img
Winand
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Avivos
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1

It is also possible to use the opencv function drawFrameAxes for this.

scale = 0.1 
img = cv2.drawFrameAxes(img, K, distortion, rotation_vec, translation_vec, scale)
HiRod
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