# How to use .getObjPoints in CharucoBoard?

**URL:** <https://forum.opencv.org/t/how-to-use-getobjpoints-in-charucoboard/14489>\
**Category:** Python\
**Created:** [September 9, 2023, 1:04am UTC](https://forum.opencv.org/t/how-to-use-getobjpoints-in-charucoboard/14489 "2023-09-09T01:04:43Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![XIvePao](https://avatars.discourse-cdn.com/v4/letter/x/e19adc/32.png) [@XIvePao](https://forum.opencv.org/u/XIvePao)\
**Post date:** [September 9, 2023, 1:04am UTC](https://forum.opencv.org/t/how-to-use-getobjpoints-in-charucoboard/14489/1 "2023-09-09T01:04:43Z")

</div>

When I generate a CharucoBoard. How do you find the positions of the Aruco Markers on the generated image?

Using getObjPoints does not work at all.  
 ![Figure_1](https://us1.discourse-cdn.com/flex020/uploads/opencv/original/2X/b/bedb35e04579ca5dbfe73e4acaf5b0d3a965c95c.png)

```auto
import sys, getopt
import time
import numpy as np

import cv2
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import matplotlib as mpl

def main():

    width = 1920
    height = 1080
    box_size = 200

    box_width_num = int(width/box_size)
    box_height_num = int(height/box_size)

    aruco_dict = cv2.aruco.getPredefinedDictionary(cv2.aruco.DICT_6X6_50)
    board = cv2.aruco.CharucoBoard((box_width_num, box_height_num), 2.0, 1.0, aruco_dict)
    img = board.generateImage( (width, height) )

    #print(board.getIds())
    squares = board.getObjPoints()

    img = cv2.cvtColor(img,cv2.COLOR_GRAY2RGB)

    for i in range(len(squares)):
        square = squares[i]
        minimum = (np.min(square, axis=0)*box_size*0.5).astype(int)
        maximum = (np.max(square, axis=0)*box_size*0.5).astype(int)

        img = cv2.rectangle(img, (minimum[0] , minimum[1] ), ( maximum[0] , maximum[1] ), (0, 255, 0), 4)

    fig = plt.figure()
    ax = fig.add_subplot(1,1,1)
    plt.imshow(img, interpolation = "nearest")
    ax.axis("off")
    plt.show()

if __name__ == " __main__":
   main()

```