A "Double" projection just uses an equivalent
sphere as an intermediate developable surface.
The NAD27 Transverse Mercator projection used for
the State Plane Coordinate systems was a "Double."
It is also known as a "Gauss-Schreiber" Transverse
Mercator. At very large scales (1:1,000) the
computational differences rarely exceed a few
tenths of a foot within a couple of degrees from
the central meridian.
With a UN small-scale map (1:5,000,000), you
cannot tell the difference. Just consider it a
spherical treatment of a Transverse Mercator.
Prof. Clifford J. Mugnier ([EMAIL PROTECTED])
Surveying, Geodesy, & Photogrammetry
LOUISIANA STATE UNIVERSITY
Department of Civil & Env. Engineering
2408 CEBA Building
Baton Rouge, Louisiana 70803
Voice & Facsimile: (225) 388-8536
====================================
See: http://www.ASPRS.org/resources.html
http://www.ce.lsu.edu/~mugnier/
====================================
----- Original Message -----
From: "George M Smith" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, September 24, 2001 6:40 PM
Subject: MI-L Double transverse Mercator
>
> Anyone familiar with a "Double Transverse
Mercator" projection. I've
> run
> across it with respect to a 5,000,000 scale
UNESCO map of Africa.
>
> Thanks
>
> George M Smith
>
>
> GeoMax Information
> www.geomax.com
> [EMAIL PROTECTED]
> 303.4404539
> 303.4404539 Fax
> GIS analysis, software and training , data
capture and manipulation
> Specialists in Geology and Minerals Exploration
>
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