title: Calculate radial velocity
body: <p>I am trying to simulate noise-filtering in a Doppler-shift radar. It should filter out objects moving below 25 m/s relative to the radar (approaching or moving away). There should be two ways of avoiding detection by the radar: if the object is moving in any direction but at a speed below 25 m/s OR moving at any speed but perpendicular to (or rather, circling) the radar. In both these cases the object's radial velocity relative to the stationary radar should be below 25 m/s and thus fool the radar into filtering it out as noise. I know the objects position and velocity vector (2D and 3D). I am a complete idiot when it comes to math so I just cant get my head around this. Any help please?</p>
  
  <p>Edit: Badly formed question. I want to get the true radial velocity relative to the radar and filter objects that are moving faster than 25 m/s but in a relative heading that would make the radial velocity towards the radar less than 25 m/s. One example would maybe be an object moving at 30 m/s and 45 degrees perpendicular to the radar would be filtered out but not if the object was moving at 300 m/s.</p>