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### `LinSphCoordinateSystem`: Combining Spherical and Linear Coordinates

Earth, space, and astronomical data often exist in a spherical coordinate space. For instance, one might want to know the longitude and latitude of a position in a satalitte image of the Earth. In addition to longitude and latitude dimensions, the dataset may have one or more additional linear axes, such as Frequency. To support this hybrid system of linear and spherical axes, the Horizon package provides the `LinSphCoordinateSystem` class.

Spherical axes are tricky because they involve a projection of a curved surface (like the surface of the Earth) onto a flat plane (the satalite's camera plane where a CCD detector is located). There are a large number of ways this projection can be done; 25 different ways are currently supported by Horizon. The linear effects that are handled by the `LinearCoordinateSystem` are also handle by this hybrid system as well. (Thus, any system that `LinearCoordinateSystem` can handle, this class can handle as well, with or without any additional spherical axes.)

You can see an example of the use of this system in support of an astronomical image in §4.2.