# how to get the actual distance between two points

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Soumya Behera on 17 Dec 2015
Commented: Image Analyst on 17 Dec 2015
I have a rectangular arena ,the length and breadth of the rectangle is known in units of centimeters ,I have an image(521*441) of the arena .How can we calculate the distance between any two points in the arena if I know the coordinates of the points in the image??

Image Analyst on 17 Dec 2015
See my attached spatial calibration demo to let you designate two points and say what the real world distance is. Then measurements you make will be reported in those, for example meters.
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Image Analyst on 17 Dec 2015
It will show you how to find the centroids. After that, you can order them in whatever order or pattern you want.

Renato Agurto on 17 Dec 2015
This should do the job:
length_cm = 30;
width_cm = 20;
length_px = 521;
width_px = 441;
length_cm_pro_px = length_cm/length_px;
width_cm_pro_px = width_cm/width_px;
% point1: (x1, y1)
% point2: (x2, y2)
dx = x2-x1;
dy = y2-y1;
distance_in_cm = sqrt((dx*length_cm_pro_px)^2 + (dy*width_cm_pro_px)^2);
cheers!
Renato
Soumya Behera on 17 Dec 2015
Yes sir your answer too helped me .Thanks a lot for that .I will create it sir but for the time being can you please help me solving it??.Thankyou