[Proj] Cosmetic latitudes...
strebe at aol.com
Fri Mar 20 20:26:56 EST 2009
On Mar 20, 2009, at 2:34:00 AM, "Mikael Rittri" <Mikael.Rittri at carmenta.com> wrote:
A) For some projections, a parameter for central latitude can be given,
but it does not really affect the shape of the map - it just creates
an extra offset in the northing values (in addition to the offset
due to the FalseNorthing).
My question: is there an established terminology for such
a central latitude?
When documenting projections, I would like to write something
like "the central latitude can be specified but is just cosmetic",
with a link to a glossary entry for "cosmetic central latitude".
But is "cosmetic" the best word?
Being merely a coordinate translation, most of the small-scale map projection literature ignores the "central latitude". Snyder includes it explicitly in his formulations, referring to it as the "latitude of origin" and denoting it as φ₀. See, for example:
Snyder, J.P. 1987. Map Projections — A Working Manual, p. 100. (US Geological Survey Professional Paper 1395). US Government Printing Office, Washington D.C.
Deetz & Adams (Elements of Map Projection) includes what is effectively the radius of the latitude of origin in their formulations of conic projections, but do not attempt to name it.
"Latitude of origin" seems sufficient and unambiguous. The central meridian and latitude of origin project to the cartesian origin. Rather than using the term "cosmetic" I would note that it is just a simple translation that does not bear on the geometry of the projection, and thenceforth label it the "latitude of origin".
— daan Strebe
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