PTgui does a nice job of stitching a flat nadir view into a panorama using viewpoint correction, provided the surface is fairly flat. Aircraft cockpits seldom have a flat deck and represent a special challenge. In fact, a tripod will not fit in many cockpits - there are few good resting spots for the three legs.
Others may be interested in the technique being developed by the author. A Manfrotto SuperClamp can be adapted with a 3/8 stud to support a Nikon D800/16mm f2.8/NN RS-2 ring mount, shown in View A in a helicopter cabin. For the nadir shot, a Manfrotto SuperClamp/Magic Arm/Camera Plate is independently attached between the mounting tube and the camera, shown in View B. Finally the quick release on the 16mm lens ring is loosened so the NN RS-2 and its clamp can be removed, leaving the camera suspended and looking down with an unobstructed nadir view, show in View C.
In this situation, taken at the same no parallax point (NPP), the nadir shots are treated like any other and will stitch on the first pass without viewpoint correction. The finished panorama looks like this:
Careful handling of the camera, firm mounting and a skillful transition are important if objects are very close. Note the stitch error on the tube just below the NPP. The clamp rotated a small amount during the switch between mounts. With the tube only about 30cm from the NPP, the image is particularly sensitive to parallax. The cabin floor shows no error, as it is farther away. Another cockpit panorama made in this way except that a tripod fit the floor for all images except the nadir:
Note the stitch error on the tube just below the NPP. The clamp rotated a small amount during the switch between mounts. With the tube only about 30cm from the NPP, the image is particularly sensitive to parallax. The cabin floor shows no error, as it is farther away.
Stitching errors are not unexpected at such close quarters but can usually be corrected in Photoshop without too much trouble. This one is relatively easy and is worth doing. See http://ge.tt/8VXWdCh1/v/0?c .
John, I was obliged to work from a screen capture of the nadir area of the displayed panorama. You would need to extract a nadir view from the equirectangular image. You can do this is various ways: e.g. the patch tool in Pano2VR, or generate cube faces with Pano2QTVR or use PTGui (http://www.johnhpanos.com/patch_view.pdf). For convenience, I rotated the view to make the bar horizontal. The basic editing sequence then went something like this:
Just completed another panorama using the same technique. In this case a tripod could be used by removing the pilot's seat cushion and placing two of the legs in the bucket seat and one against the bottom of the control column. After the separate clamps were added to suspend the camera in the nadir position, the Nodal Ninja head was disassembled, the tripod removed, and the seat cushion replaced for the nadir shot:
(However don't bump the pilot's harnesses in the process or you will end up with a stitching error that needs to be fixed... as can be seen.)
The image features a very wide depth of field, accompanied by seven stops of exposure-fused bracketing, and hidden battery-powered LED lamps for areas in the the shadows such as the rudder pedals. Another panorama in the nose of the aircraft was made in the same way:
Two recent examples of this technique... suspending the camera from the aircraft canopy on interior structure, and removing the tripod for the nadir shot. How nice to have the nadir image stitch like the others, without viewpoint correction: