I do want to model something that i a have photographed in 2 different perspectives.
So after modeling it looking through one camera, i do want to slide the vertices back and forth along the vector describing the direction between camera origin and vertex position (and not the view axis, because that would always be the same direction for every pixel of the image)
It's like creating a vertex while viewing from a fixed position/rotation, than making an edge to the viewing origin and vertex sliding the first vertex without clamp.