How to enter the real world units and distance while doing the spatial calibertion?

I'm very much thankful to you analyst. I'm really appreciating your work on spatial_calibration demo . But I had a doubt on the spatial calibration. Here it is,

1. Suppose if we consider the "cameraman" image, which is given in the menu of demo, and I wanted to know his height in terms of feet or meters. In such a case how to do the calibration, when it is asking like choose the real world units and enter the distance in that units.

2. In another case, that too in the case of "coins" image, the distance between any to coins usually may be in terms centimeters, in such a case how to get the actual distance that exists there.

Since I'm not getting the distance that is actually present. Please I'm kindly requesting you to help me out on how to give the values while doing the spatial calibration in such scenarios or situations.

Thank you.

Answer 1

[Image Analyst]

You have to have something to measure first that is of known dimensions (lengths, distances). For example if I had an image of the moon, how do I know it's the real moon from through a telescope instead of a poster on the wall? Well you have to measure some known distance, for example a ruler on the wall next to your poster, or the diameter of the moon if you know it's the real one. Once you enter that known distance then you can go on to measure any arbitrary distances or areas in the image.

[Balakrishnan Sekar]

Sir,thank you so much for providing the demo file. It is very useful. Sir in my work, I am in need of measuring diameter of a circle. I couldn't understand the concept of choose the real world units and enter the distance in that units. I want final output diameter in mm. What is that distance in that units ? Should I enter diameter of the circle ??? Could you please explain me.