# How to compute the 3D location of a 2D point on the ground?

I know the focal length f and the principal point of a camera P(x,y) and I can assume the ground plane is orthogonal to the image plane.

I have a 2D point on the picture that I know is on the ground, how do I get it on 3D using camera coordinates. However I am not sure how to approach this? Any advice is appreciated.

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Sort by » oldest newest most voted Do you simply want the range from the camera? Or do you need precise 3d location?

Either way you need

1. The focal length in mm or the size of the FPA in mm.
2. The height above the ground.
3. If you want the precise 3d location, you need where the camera is, over the ground.

This assumes the point you want is level with the ground. If it is notably off the ground, you can't do it with one stationary camera.

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If I have an x,y I need to get an x,y,z for some point x,y but I am not sure what the mathematical process is. Can you help me ? I could implement the algorithm myself

You need the height of an object? And you know the xy of the camera and the xy of the object?

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