pcl_viewer needs a camera scale option

I have a point cloud taken from very, very close, such that the distance between points is on the order of 1E-5. Unfortunately, when I try to view it in pcl_viewer, it shows up as what appears to be a single point.

I can partially address this by changing between perspective and parallel projection and then very carefully zooming in on it. But eventually I get to a point where the camera motion is too big to properly center it for additional zooming.

It seems like the appropriate fix is to scale the vtkCamera. Unfortunately, I can't figure out where the code for events in pcl_viewer is even located (I spent an hour looking for it last week and no luck).

If someone could point me in the right direction, I may be able to add this option. Or if the option already exists, let me know so I can document it. =)

The issue identifies pcl_viewer and vtkCamera but no source file or test. Start by tracing pcl_viewer’s camera-event handling and checking whether an existing projection or zoom option covers this case. Done means defining and documenting a camera scale option that lets very close point clouds be centered and viewed.