How to determine the speed of the car that overtook you?

Question

Machine learning

Good afternoon!
How to determine the speed of the car that overtook you?
There are:
- its exact constant speed (by gps);
- there is a video from your car, the camera looks straight ahead;
- the overtaking car was in a parallel lane.
What methods can be used to solve this problem?
Thanks

Answer 1

1. Select two frames from the entire video between which the speed is measured, the car on these frames should be as close as possible (to make it easier to measure the distance to it), but the distance between the frames themselves should be larger (to reduce the measurement error).
   
2. Determine the distance to the car on each of the two frames (no way without it, alas). To do this, you can photograph a car of similar dimensions from the same angle until its position in the picture exactly matches the position of the measured car in the frame from the registrar, then accurately measure the distance to some point (near wheel, for example).
   
3. Determine the angle at which the car is to your axis of motion and the center of the recorder frame (I hope they match) in each frame. To do this, as well as in (2), you can move and photograph a car similar in size.
   
4. Knowing the distance and the angle on two different frames, a triangle is built and its unknown side is found (if the other two sides and the angles to them are known).
   
5. Knowing the frame rate, the time between two frames is calculated (it is desirable that it be more, but not so that the car is already too far on the second frame).
   
6. Distance divided by time equals speed. This is the overtaking speed, the absolute speed can be obtained by adding the own speed.
   

Answer 2

The simplest basic option, like in cameras on the roads:
1 The size of the license plate in Russia is 99% standard
2 When overtaking, a series of pictures are taken
3 The measurement of the size of the license plate is compared
4 The speed is calculated with cunning mathematics (I will look for a theory in the evening)

Answer 3

Estimate the distance according to the situation, the average length of the car and so on. You have time - from the video. Get the relative speed, and from it - the absolute.

Answer 4

You can try to calculate, calculate the dynamics of changes in some linear size of the car - for example, state. numbers or better the distance between the headlights. So right away, of course, I won’t give the formula, but it seems to be computable.