Here is a sequence I restitched recently using this new method
http://www.dropbox.com/s/0ktc8nc68y3u4hm/hemi1.mp4 (115Meg)
side by side fisheye 180 (looking down = hemispherical 3d 360)
looks good in Whirligig (stereo dome, pitch -90 ) or LiveViewRift (pitch -90, mapping equid, equid r 1.00 )
details:
PTGui panorama stitching software has an option, Viewpoint optimisation, which is mainly used for creating seamless nadirs with image sequences with 2D still panoramas sequences where there is parallax between successive shots. It effectly parallelises the cameras to the ground plane I guess. It occurred to me -- eventually -- that this would be a good way of calibrating the 3 downward cameras in a ground facing Iximage type arrangement. And it does give much more perfect stitching.
The reason being the Iximage arrangement gives good horizontal stitching along axes where the other two lenses are visible at the periphery of any one of the three lens. But good vertical stitching only at one chosen subject distance.
Originally I was using distant points to calibrate the cameras, as distant points are not affected in their image locations by the non- zero -parallax nature of the camera configuration. But that meant all closer features had vertical parallax stitching errors along the three vertical blending lines. By using viewpoint optimisation with the ground plane as the source of the matching features you get the ground plane distance from the camera rig as the zero vertical parallax subject distance. So you can, by using a variable height monopod say, set the ground plane where you like, when you shoot a calibration video sequence. And the calibration is very robust and repeatable compared with not using Viewpoint optimisation.
