[Proj] Terminology for origins, and everything
Gerald I. Evenden
geraldi.evenden at gmail.com
Fri Oct 3 13:58:17 EDT 2008
The problems with the variety of nomenclatures is going to persist until some
lingua franca of cartography is established. If I recall correctly, if you
are a pilot that flies internationally, all you need to know is English to
communicate with any airport control tower. Similarly we need something
similar restriction for describing cartographic projections.
In the case of origins I feel the case is simply:
1. Designate the names of the two coordinate systems involved such as
geographic and Cartesian. A "projection" transforms information in one
coordinate system to and from the alternate system. For this case the
coordinate systems axis are called latitude and longitude for the geographic
system and easting and northing for the Cartesian system.
2. If "base" geographic coordinates, lat_0 or lon_0, are specified then they
represent the location in geographic space of the Cartesian system origin.
When either lat_0 or lon_0 are not specified then they are respectively
assumed to have a 0 value unless otherwise specified. Other projection
conditions that may be caused by their usage require additional description.
3. "False" eastings and northings are values that are added to the respective
easting and northing coordinates and thus offset the coordinates from their
origin. Usage is normally restricted to grid systems in order to maintain
positive Cartesian values over the region of application. Omission denotes 0
This is a suggested starter. Something for heated debate and resolution.
I, for one, wish to refine item 1. into parts that refine the use of the
term "projection" so as to ensure that it does not expand to include other
issues. A strict use of the meaning of "cartographic projection." This is
obviously reminiscent of much earlier debates of including datum shifts into
proj, etc.. ;-)
An interesting factor about item 2. is that one projection prohibits (or
ignores in proj's case) the specification of lat_0: UTM.
My terminology for geographic and Cartesian are certainly open.
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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