Computed point cloud centroid?

[msobanion]

Hello,
Thank you for your help back in August! I ended up using your point normal shader code in a per-point uncertainty calculation and visualization shader I developed for TLS point cloud data. At this point in time, it is meant for only one scan position but I hope to incorporate registration error for multi-scan point clouds and maybe even airborne lidar in the future. I have written a paper that will be published in the ASCE Journal of Surveying Engineering and I plan to upload my shader code as an open-source software resource to be used with Displaz. Before the paper is finalized for publication and the shader code is uploaded I had a question:

While developing this shader, I ran into some interesting behavior when I displayed back-calculated values for horizontal angle (0 to 360 degrees for TLS) based on a scan origin of (0,0,0). When visualizing the change in horizontal angle of the points with a color ramp, the origin of rotation appeared offset from the actual scan origin. I was able to fix this by manually editing the ply point cloud file to include a fake point located at 0,0,0. Any idea why this might be happening in Displaz, like an auto computed point cloud centroid or something? It would be great if manual editing of the ply file was not necessary.

Thank you again for creating Displaz, it was very helpful for the development of my uncertainty shader. I have cited your creation of Displaz in the paper and added you to the acknowledgements.

Matt O'Banion