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The transverse Mercator was invented by Lambert in 1772.
In this projection the cylinder touches a meridian along
which there is no distortion. The distortion increases away
from the central meridian and goes to infinity at 90o from
center. The central meridian, each meridian 90o away
from the center, and equator are straight lines; other parallels
and meridians are complex curves. The projection is defined
by specifying:
- The central meridian
- Scale along the equator in inch/degree or 1:xxxxx (-Jt), or map width (-JT)
Our example shows a transverse Mercator map of south-east
Europe and the Middle East with 35oE as the central
meridian:
pscoast -R20/30/50/45r -Jt35/0.18i -B10g5 -Dl -A250 -G200 -W0.25p -P >! GMT_transverse_merc.ps
Figure 5.18:
Rectangular Transverse Mercator map
 |
A particular subset of the transverse Mercator is the
Universal Transverse Mercator (UTM) which was adopted
by the US Army for large-scale military maps. Here, the
globe is divided into 60 zones between 84oS and
84oN, most of which are 6o wide. Each of
these UTM zones have their unique central meridian.
GMT implements both the transverse Mercator and the
UTM projection. When selecting UTM you must specify:
- UTM zone (1-60). Use negative value for zones in the southern hemisphere
- Scale along the equator in inch/degree or 1:xxxxx (-Ju), or map width (-JU)
In order to minimize the distortion in any given zone,
a scale factor of 0.9996 has been factored into the formulae.
The scale only varies by 1 part in 1,000 from true scale at
equator.
Next: Oblique Mercator (–-Jo -–JO)
Up: Cylindrical Projections
Previous: Mercator Projection (-–Jm -JM)
Paul Wessel
1999-03-25