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The conventional suffix for `SPHERE`

files is `.sph`.

[ST][E|H|S]SPHERE # Keyword # auto-generated texture co-ordinates, only allowed withSTSPHERE objects [SINUSOIDAL|CYLINDRICAL|RECTANGULAR|STEREOGRAPHIC|ONEFACE] # next four fields are requiredRadiusXcenterYcenterZcenter

The key word is `[ST][E|H|S]SPHERE`

.
The optional prefix characters mean:

- `
`ST`' - The sphere carries automatically generated texture co-ordinates. See below.
- `
`E`' - The sphere lives in Euclidean space.
- `
`H`' - The sphere lives in Hyperbolic space. See Non-Euclidean Geometry.
- `
`S`' - The sphere lives in spherical space. See Non-Euclidean Geometry.

Sphere objects are drawn using meshes which are rectangular in a polar
co-ordinate system, with the equatorial plane parallel to the
`x,y`

-plane. Their smoothness, and the time taken to draw them,
depends on the setting of the dicing level, 10x10 by default. From
Geomview, the Appearance panel, the `<N>ad`

keyboard command, or a
`dice nu nv`

Appearance attribute sets this.

Texture co-ordinates are generated for `STSPHERE`

objectes; the
keyword following the initial `STSPHERE`

keyword defines the way
this is done. It follows the conventions of the `mktxmesh`
Perl-script which comes with the *Orrery*.

`SINUSOIDAL`- sinusoidal equal-area projection
`CYLINDRICAL`- cylindrical proj:
`s`is the longitude,`t`is the latitude `RECTANGULAR`- rectangular proj:
`s`is the longitude,`t`is`sin(latitude)`

(i.e.`z`

co-ordinate in the sphere's co-ordinate system) `STEREOGRAPHIC`- stereographic projection from the south (
`z=-1`

) pole `ONEFACE`- stretch orthographic view of
`+y`

hemisphere over both, mirroring