# Geometry :

Subject: Re: [geometry] Support for geographic coordinate system
Date: 2014-11-18 18:17:05

Hi Barend,

Barend Gehrels wrote:
> Sure, it makes sense and I agree (a bit). While srs describes a
> spatial reference system, it includes a reference ellipsoid. So the
> spheroids can be part of the namespace srs, defining also other
> things. But yes, it is GIS-specific. But isn't the whole geographic
> coordinate system GIS-specific?
>
> called a refererence ellipsoid.

>
> You earlier mentioned that we should call it a spheroid, because the
> Earth is in fact spheroid-shaped, so it is mathematically more correct
> to call it a spheroid. For the Earth it is. But that makes it
> GIS-specific too...
>
> Each spheroid is an ellipsoid, where two axes happen to be the same.
> But there are also bodies which are true ellipsoids, e.g. Jupiter's
> moon Io (same article). So yes, why not call it in general an
> ellipsoid, it is one, and that is the common name...
>
> If we have that, we can use the namespace re (reference ellipsoid).
>
> The model we are currently defining, of course, you can then still
> call a spheroid because it defines only two axes.

Yes, that's exactly the reason. An ellipsoid may define 3 different
axes. Currently we're unable to support such case.

>
> So it then becomes for example:
>
> boost::geometry::re::spheroid<>
>
> srs is for me still an option too
>
> Another alternative is "datum" which has the advantage that it is not
> an abbreviation. Geodesic datum contains a reference ellipsoid and
> more, but as a namespace it might be convenient.
>
> boost::geometry::datum::spheroid<>

From the above I prefer srs. re may be confusing (complex Re) and datum
seems to be even closer to geography/geodesy than srs.

So, let's sumarize, in the ascending order of preference (though I'm not