What are the parameters that I need to consider when figuring out the horizontal viewing distance of a camera mounted overhead for effective tracking?

Question

I am currently working on developing a hybrid Indoor Positioning system where images from an overhead camera will be used to identify and track people.

I am new to the field of visual tracking and a challenge that I have recently faced was choosing a suitable camera/lens combination.

My question is what are the parameters that would help me choose the right camera with the right field of view?

To clarify, I installed a raspberry pi camera module v2 on the ceiling and recorded its video output wirelessly. It seems the field of view was too small for looking at the scene effectively. My conclusion is there must be some techniques/equations which can guide me in choosing the horizontal view distance of the camera in relation to its height from the ground floor.

Answer 1

A field of view of a camera is generally measured in degrees. If you connect the imaginary focus point of the lens with two sides of the camera sensor, in case of rectilinear lenses, you get your field of view. Obviously you can do that in the horizontal and in the vertical direction, you get practically two different fields of view. Usually the wider one is considered the field of view, and the other one is linked to the previous one by the aspect ration of the sensor (e.g. 16:9).

So the physical size of the imager and the focus length are what influence the field of view.

Den pending on the distance resolution might be important. Given a flat surface you are filming, perpendicular to the camera's optical axis , given the field of view, the physical size of the sensor and its resolution, using simple geometry, it can ba calculates how many pixels of the sensor will be used to register 1mm on the surface. This will be important to see if e.g. a QR code can be read by the camera or not.

For fisheye lenses, the calculations are not this simple, but are analogue. This page describes how fisheye lenses are modelled. For a Field of View, similar as in the rectilinear case, the angle between the outermost rays hitting the sensor have to be calculated.