Fixing nadir parallax errors

Here is a set of source photos for a spherical panorama:

They were taken using a one second exposure without a tripod, the camera was stabilised by jamming it against the sides of a palm tree. This means that they don't stitch easily because of the large (approximately 60cm) parallax error:

Particularly, the nadir doesn't work at all. This is an extreme version of the usual problems caused by failing to rotate the camera around the No-parallax point:

However the nadir can be stitched by taking advantage of another technique generally used for stitching a linear panorama. The way this works is that if you assume the ground forms a plane just like a mural on a wall; a series of rectilinear Projection images taken from different locations can be assembled by optimising roll, pitch & yaw, Field of View and d & e lens correction parameters separately for each image.

So the first step is to create a series of defished rectilinear images from the fisheye Projection originals. You can do this in any of the GUI front-ends, but you do need to calibrate your lens first:

These can then be stitched together into a single rectilinear Projection image of the nadir with minimal errors. Effectively this is plan view of the ground surface:

This plan image can then be reinserted into the original panorama project as if it was another source photo with a different lens, and then stitched as normal by optimising roll, pitch, yaw, Field of View and d & e lens correction parameters. Here is the result as a QTVR:

<pano file="Npx-corrected.mov" width="600" height="450" scale="tofit" controller="true" cache="true" />

This scene is of the Abu Dhabi corniche, 30th November 2006. The buildings are decorated in preparation for UAE national day.