Outside Ray to Box intersection
Now that we have intersection of rays inside a box, we have to think about intersection of rays outside a box.
So we have a box with corner edges imgPos - halfPixel and ending at imgPos - halfPixel + nRows*BinWidth
and a proton starting in vacuum, outside the patient, for example 1 meter away, with a slight angle 0.1deg or so. The idea is to calculate at what position xyz it intersects with that big box. Or if it misses it, in which case it should return a NaN or so.
Also ctest for this.