How to Make Panoramas for Celestia


0.0: Introduction.

Panoramas are pictures which surround you, giving you the impression that you are there. Since they're only pictures, they may be easier to make than full 3D models of a location.

Panoramic images only look right if your viewpoint is at a specific position, usually at the center. You can look in all directions without distrubing the illusion. If you move away from that position, however, then all the proportions of the projected image become distorted.

Three of the panoramic projections that are used quite often are spherical, cylindrical and cubical.

Most VRML programs are used only to display panoramic images. The 3D objects below make it easy to view panoramas within Celestia.

After you've gone to the center of a panorama within Celestia, here's how you can enable the "Alt-Az" arrow key mode so that you can turn your viewpoint appropriately.

  1. Orient your viewpoint so the horizon is horizontal.
  2. Select the planet on which the model is positioned.
  3. Select Sync Orbit mode (type a y)
  4. Enable Alt-Azimuth mode (type a Ctrl-F)
  5. The left and right arrow keys now will turn your viewpoint properly.

Alternatively, you can put your computer's numeric keypad into "numeric lock" mode and then use the 4 and 6 keys to rotate to the left and right.

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1.0: Spherical Panoramas.

Spherical panoramas are projected onto the inside of a sphere.

Flat images that cover the entire spherical viewing angle (four π steradians) around the observer are produced in any of a variety of projections. Hammer-Aitoff seems to be the most common, although many are available as "simple cylindrical."

Spherical panoramas often are created by astronomers to display all-sky maps.

An image must be in "simple cylindrical" format for use with this model. This is the same projection format as is used for surface texture maps that are placed on the outside of planetary bodies within Celestia.

Software that does a good job of converting Hammer-Aitoff images into simple cylindrical is hard to find. Iris by Christian Buil is one such utility, but it has some problems: I've found it very difficult to avoid a pole-to-pole seam.

For more details, see the file sphere-pano/readme.txt within the Zip archive.

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2.0: Cylindrical Panoramas.

Cylindrical panoramas are projected onto the inside of a cylinder. An image to be used as a cylindrical panorama should show 360 degrees around the observer, but there's no standardized height. Usually they've been constructed from many pictures taken in a circle around the viewpoint.

Cylindrical panoramas often are created by photographers. There's a large variety of software available to stitch photographs together into cylindrical panoramas.

The easiest way to place a cylindrical panorama within Celestia is to project it onto the same spherical 3D model as is described in section 1 above. Scale the panoramic image if necessary, and pad its top and bottom to make its dimensions (in pixels) a power of two on a side. There may be some mild distortion of the perspective near the top and bottom of the resulting image, but it's usually not noticable.

For more details, see the file sphere-pano/readme.txt within the Zip archive.

A sample cylindrical panorama is included in the Zip archive above. Here's a screenshot showing it being used within Celestia. It's an anaglyph (red/blue) 3D panorama of Columbia Memorial Station recently taken by the Spirit excursion vehicle on Mars.

[Columbia Memorial Station]
Columbia Memorial Station in 3D
Here's a Cel:// URL to take you to this viewpoint.

Columbia Memorial Station

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3.0: Cubical Panoramas.

Cubical panoramas consist of 6 square pictures, each covering about 90 degrees. Four of them combine to display the horizon around the observer, one shows the view above, and the sixth shows what's below the viewpoint.

Cubical panoramas often are created using programs like Terragen.

Two types of cubic bodies are available here. The first projects a single image, applying different parts of it onto the different faces of a cube. The other projects six separate images, one onto each face.

For proper positioning within Celestia, the north pole of the cubes is at the center of the "top" face, tile #5, while the prime meridian passes vertically through the center of tile #1.

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4.0: Aligning Panoramas.

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5.0: Acknowledgements.


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A.0 Appendices.