Fixing nadir parallax errors

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corrected with [[vertical control points]]:
 
corrected with [[vertical control points]]:
  
<pano file="npx-corrected.mov" width="600" height="450" scale="tofit" controller="true" cache="true" />
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<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
 
This scene is of the Abu Dhabi corniche, 30th November 2006.  The buildings are decorated

Revision as of 01:37, 15 December 2006

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 nadir image with minimal errors, in this case I chose a fisheye projection, though a rectilinear or equirectangular projection would work just as well:

Npx-corrected-nadir.jpg

This image can then be reinserted into the original panorama project as another source photo with a different lens and stitched as normal. Here is the result as a QTVR, the buildings in the distance are a bit wobbly, but this could have been corrected with vertical control points:

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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