# Draw a triangle with centroid using OpenCV

• Difficulty Level : Medium
• Last Updated : 18 Dec, 2018

Prerequisite: Geometric shapes using OpenCV

Given three vertices of a triangle, write a Python program to find the centroid of the triangle and then draw the triangle with its centroid on a black window using OpenCV.

Examples:

Input: (100, 200) (50, 50) (300, 100)
Output: (150, 116)


Libraries Needed:

OpenCV
Numpy


Approach:
Create a black window with three color channels with resolution 400 x 300. Draw three lines which are passing through the given points using the inbuilt line function of the OpenCV. It will create a triangle on the black window. Find the centroid of the triangle using the following simple formula. Draw this centroid on the black window using circle function of OpenCV with zero thickness.

Below is the implementation of the above approach:

 # Python3 code to draw a triangle and find centroid  # importing librariesimport numpy as npimport cv2  # Width and height of the black window width = 400height = 300  # Create a black window of 400 x 300img = np.zeros((height, width, 3), np.uint8)  # Three vertices(tuples) of the triangle p1 = (100, 200)p2 = (50, 50)p3 = (300, 100)  # Drawing the triangle with the help of lines#  on the black window With given points # cv2.line is the inbuilt function in opencv librarycv2.line(img, p1, p2, (255, 0, 0), 3)cv2.line(img, p2, p3, (255, 0, 0), 3)cv2.line(img, p1, p3, (255, 0, 0), 3)  # finding centroid using the following formula# (X, Y) = (x1 + x2 + x3//3, y1 + y2 + y3//3) centroid = ((p1+p2+p3)//3, (p1+p2+p3)//3)  # Drawing the centroid on the window  cv2.circle(img, centroid, 4, (0, 255, 0))  # image is the title of the windowcv2.imshow("image", img)cv2.waitKey(0)

Output:

(150, 116) My Personal Notes arrow_drop_up