Fixing nadir parallax errors

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Revision as of 19:09, 21 March 2007 by Erik Krause (Talk | contribs)

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

Npx-uncorrected-originals.jpg

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:

Npx-uncorrected-equirectangular.jpg

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:

Npx-uncorrected-nadir.jpg

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:

Npx-rectilinear-extracted.jpg

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:

Npx-corrected-nadir.jpg

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:

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

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