[GRASSLIST:4683] Re: robinson projection

[Glynn Clements]

Glynn Clements wrote:

> Second, the equations which describe many of the projections are
> periodic (especially in longitude), and the inverse of a periodic
> function is multi-valued (e.g. sin(t) = sin(t + 2.n.pi) for all
> integral n, so if k = sin(t), arcsin(k) is the set {t+2.n.pi} for all
> integral n rather than a single value).

Sorry, I'm getting confused. Periodicity of the equations is more
usually an issue for latitude. Cylindrical and pseudo-cylindrical
projections typically have a non-periodic correspondence between
longitude and easting.

In that situation, horizontal periodicity is due to longitudinal
"wrapping", i.e. 270E == 90W. However, the net effect is the same; as
the wrapping occurs inside the PROJ library, r.proj can't do anything
about it.

-- 
Glynn Clements <glynn at gclements.plus.com>