Finding length of an object with camera

HI,

I want to find the dimensions of objects with camera in 2D plane, so please suggest me some possible methods. I can use a reference object in that image like card etc, to which i am also able to calculate distance from the camera, i.e i know the distance, and the dimensions of the marker, just suggest me some coding, formula or method to find the dimensions in a 2D plane with respect to the reference object(marker).

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/vision/examples/measuring-planar-objects-with-a-calibrated-camera.html

[muhammad]

Dear i want to find the linear distances

Answer 2

[Image Analyst]

See my spatial calibration demo, attached.