[Proj] Mercator Problem

Gerald I. Evenden gerald.evenden at verizon.net
Wed Oct 19 14:43:12 EDT 2005

I've tried to stay out of this problem but it persists.  Mugnier's statement 
below is the best response to the original problem although it should be 
added that the normal Mercator is useful as a conformal projection of areas 
with east-west extent near the equator.

The only viable means of determining distance between points is by means of 
any one of the geodesic formulas available.  The program 'geod' in the old 
proj4 distribution uses one of these methods.  Vincenti's from the Geodetic
Survey is a slightly better method and is available as FORTRAN code.

If the points involved are in a local grid system or from a map, invert them 
to geodetic coordinates and use above methods.

With current computing equipment and methods I don't think we need to resort 
to good-old-day methods for computing the distance between points.

On Monday 17 October 2005 03:51 pm, Clifford J Mugnier wrote:
> The Normal Aspect of the Mercator projection has only one practical
> application, and that is for computing a Loxodrome or Rhumb Line with the
> associated geometric manipulations/intersections of that line with the
> graticule, etc.  Computing distances is a folly on the Normal Aspect
> Mercator.  With two endpoints, just compute the inverse of the cartesian
> coordinates back into latitude and longitude and then compute the correct
> distance with a geodesic inverse.

Jerry and the low riders:Daisy May and Joshua
"The being cannot be termed rational or virtuous,
who obeys any authority, but that of reason."
---Mary Wollstonecraft 1792

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