HowTo:Extract 2D screen coordinates from 3D scenes

Introduction

At some point in your POV-Ray career you may need to retrieve high precision 2D screen coordinates of a point in a 3D POV-Ray render. Simply measuring the number of pixels in MS Paint is rarely a good solution because the precision is too low, even for very large renders. Instead, you need to use POV-Ray's own mechanisms to calculate and output finer measurements.

I faced this problem when designing two images for Wikipedia. For the first image, I needed to overlay 2D vector elements on top of a 3D POV-Ray render in order to show a series of measurements I made of important angles in the 3D bitmap. For the second image, I used the points outputted from a POV-Ray render to create a brand new 2D vector image from scratch. In both cases I used GeoGebra to create the 2D vector elements, but you could use InkScape as well.