RFC: Astro::ECI (or Astro::Coord::ECI, or ...)

All,

I have been attempting to put together some satellite tracking (or at least observing) modules in Perl. The code has fallen into three (so far) modules: one representing the satellite, one representing the Sun, and a superclass representing "static" (i.e. Earthbound) coordinates and providing all the coordinate transformations. For the sake of discussion, call the superclass Astro::ECI (for Earth-Centered Inertial), and the subclasses Astro::ECI::TLE (for Two- (or three-, both are handled) Line Element), and Astro::ECI::Sun (an exercise for the student).

The question is, what should I actually call these things? Does Astro::TLE cut it, or do people think something like Astro::Coord::TLE would be better? Or something else? I assume that if the superclass changes names the subclasses will too, though Perl does not require it.

There's about 50% overlap between Astro::ECI (or whatever) and Astro::Coords. The differences that come to mind are:

* Astro::Coords doesn't seem to be interested in the Earthbound side of things. Astro::ECI does ECI (of course), geocentric Cartesian, geocentric latitude/longitude, and geodetic latitude/longitude, with a mechanism for user-defined reference ellipsoids. Different objects can use different ellipsoids

* Astro::Coords relies on Astro::SLA and SLALIB, whereas Astro::ECI is pure Perl.

* Astro::ECI is designed to be the superclass for a position predictor. I can't really say about Astro::Coords.

* Astro::Coords spends a fair amount of time and effort worrying about alternate representations of data (hour angles, degrees/minutes/seconds of arc ...). Astro::ECI is radians and kilometers, period.

* Astro::Coords uses either Time::Piece or DateTime objects. Currently, Astro::TLE uses scalar times, though it may support DateTime in the future (and the check is in the mail ...).

* Astro::Coords is published under the GPL. I intend to publish under the Perl Artistic License.

There's not as much overlap between the proposed Astro::ECI::Sun (or whatever) and the Astro::Sun.* modules as might appear. Astro::ECI::Sun calculates the position of the Sun at any given time, whereas the Astro::Sun.* modules calculate local sunrise/sunset. The superclass provides a method that gets you sunrise and sunset (or begin/end twilight), and another for meridian passage (local noon, local midnight). I _think_ that Astro::Coords will give the position of the Sun and Moon, at least.

Astro::ECI::TLE implements the NORAD SGP.* and SDP.* orbital models. If there's anything remotely similar in CPAN, I haven't found it.

Both suggestions and metasuggestions (i.e. possible additional or alternate places to take the questions) are welcome. I can't guarantee what will come out of all this, because I still need to figure out what permissions I need before I publish, and whether I can get them.

Thanks,
Tom Wyant (mailing address to the contrary notwithstanding)
.

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