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Cylindrical vs. Spherical Projection

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Phil Steer
Posted on Saturday, August 05, 2000 - 2:11 am:   Edit PostDelete Post

Could you explain the difference between cylindrical and spherical projection? In particular, which should you use when creating:

i) a flat 360 degree panorama?
ii) a panorama for display with Panorama Tools PTViewer?

Many thanks.
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John Strait
Posted on Monday, August 07, 2000 - 10:22 pm:   Edit PostDelete Post

In cylindrical projection, the image is first mapped onto the surface of a cylinder and then the cylinder is unrolled. See http://mathworld.wolfram.com/CylindricalProjection.html for a nice schematic drawing of cylindrical projection.

What The Panorama Factory calls a spherical projection is more correctly termed "equirectangular projection." The horizontal coordinate is the longitude and the vertical coordinate is the latitude. See http://mathworld.wolfram.com/EquirectangularProjection.html.

Swing-lens cameras (e.g. Noblex, Widelux, Horizon)
and rotational cameras (e.g. Cirkut, Roundshot, Panoscan) produce cylindrical projections. In these cameras, the film is effectively bent into a cylinder within the camera when the film is exposed.

Equirectangular projections can't be produced in a physical camera because the film would need to be bent in two axes at the same time. That is, the film would have to be bent onto a section of a sphere.

Each type of projection produces its own characteristic distortions. See http://www.fh-furtwangen.de/~dersch/PTVJ/doc.html to see the same image shown with both types of projection.

Cylindrical projection cannot reproduce the full 180 degree vertical field of view from floor to ceiling without using an infinitely tall piece of paper! For this reason, full 180x360 viewers usually require equirectangular panoramic projection.

PTViewer requires equirectangular panoramic images (referred to as spherically reprojected in The Panorama Factory).

When preparing images for printing or for online display as a "flat 360," the choice of cylindrical or spherical reprojection is largely an esthetic choice. Personally I prefer the spherical reprojection, but that's really a personal choice.
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Unregistered guest
Posted on Tuesday, April 12, 2005 - 6:15 am:   Edit PostDelete Post


I'm using an equiangular mirror and I'm obtaining a 360 image. I would like to make a code to unwarp it, but i don't know how.
Can you help me,
Many thanks

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