Detect Shapes in an array of points

Question

Hello

I have an array of points. I want to know if this array of point represents a circle, a square or a triangle.

Where should i begin? (i use C#)

Thanks Jon

Answer 1

I'm going to take a wild stab and say if you have 3 points the shape represents a triangle, 4 points is some kind of quadrilateral, any more than that is a circle.

Perhaps there's more information to your problem you could provide.

Answer 2

imagine it is each of these one-by-one and try to fit each of these shapes on the data.. for a square, you could find the four extreme points, and try charting out a square that goes through all of them..
Once you have got a shape in place.. you could measure the distance between each of the points and the part of the shape that is nearest to it.. then square these distances and add them up.. the shape which has the smallest sum-of-squares is probably your best bet

Answer 3

Use the Hough Transform.

Answer 4

Depending on your problem, a good approach for this problem may be to use the Hough transform and all its derived algorithm

It consists in a transformation of the image space to an other space where the coordinate represents the objects parameters (angle and initial point for a line, coordinates of the center and radius for a circle)

The algorithm transforms each point of your array of points in points in the other space. Then you have to search in the new space if some points are prevailing. From these points, you will get the parameters of your object.

Of course, you need to do it once to recognize the lines (so you will know how many lines are in your bitmap and where they are) and to it to recognize the circles (it is not exactly the same algorithm)

You may have a look to this lecture (for Hough Circle Transform), but you could easily find the algorithm for line

EDIT: you can also have a look to these answers

Shape recognition algorithm(s)

Detecting an object on the image based on geometrical form