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Transverse (-–Jt -–JT) & Universal Transverse Mercator UTM (-–Ju -–JU)

           

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:

$\bullet$
The central meridian

$\bullet$
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
\begin{figure}\centering\epsfig{figure=eps/GMT_transverse_merc.eps}\end{figure}

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:

$\bullet$
UTM zone (1-60). Use negative value for zones in the southern hemisphere

$\bullet$
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 up previous contents index
Next: Oblique Mercator (–-Jo -–JO) Up: Cylindrical Projections Previous: Mercator Projection (-–Jm -JM)
Paul Wessel
1999-03-25