[Proj] Re: "Double ellipsoid" case?

Gerald I. Evenden geraldi.evenden at gmail.com
Wed Dec 3 14:27:22 EST 2008

On Wednesday 03 December 2008 1:43:19 pm Christopher Barker wrote:
> >> The practical consequence is that they do not have a conformal
> >> projection; hence local distances measured from a point are not quite
> >> uniform in all directions,
> measuring distance is a problem with Mercator anyway -- the scale varies
> with latitude -- a lot more that difference between a sphere and an
> ellipsoid.
> One thing that IS absurd is that Google maps puts a scale bar on every
> map -- even the whole earth scale, where it is essentially meaningless.

Frankly, it is silly and misleading to put a scale bar on any map.  Even for a 
conformal map a scale bar is superfluous because the scale issue only applies 
to an infinitely small segment of the map.  Attempting to make a measurement 
over any finite distance is subject to error that is ever increasing with 

The *ONLY* method of measuring distance is with geodesic software and knowing 
the geographic coordinates of the points in question.

Yes, people with continue to put scale bars on maps but *NEVER* use anything 
more precise than your knuckles or finger span when measuring distances with 
one.  That will remind you of the limitation of such a tedius and meanless 
cartographic icon.

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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