How to Measure the Distance Between the Red crosses?

I am trying to do shape identification using the harris corner detection method. I want to detect 2 corners of a shape and use the distance between those corners to identify the shape (square, triangle, circle, or star). How do I measure the distance between the red crosses in the picture below? How would I then classify that distance as a triangle?

Answer 1

[Abhisek Pradhan]

imdistline can be used to find the distance between two points in an image by interactively setting the positions. For detecting whether the image is a triangle or not I would suggest referring the example in below-mentioned links. Or we may need to get the length of all three sides to conclude it to be a triangle.

https://www.mathworks.com/matlabcentral/answers/289472-how-can-i-detect-triangle