[R-sig-Geo] function to convert 3D geographical coordinates to Cartesian?

[Tom Roche]

Is there packaged code to convert geographical coordinates (e.g.,
longitude, latitude, elevation) to Cartesian coordinates in 3-space?
The spherical-to-Cartesian math is straightforward enough, but there's
certainly scope for error, so I'd prefer to use tested, previously-used
code if available.

TIA, Tom Roche <Tom_Roche at pobox.com>