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## Transverse Mercator (-–Jt -–JT)

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

  The latitude of origin

  Scale along the equator in inch/degree or 1:xxxxx (-Jt), or map width (-JT)

The optional latitude of origin defaults to Equator if not specified. 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 5.19: Rectangular Transverse Mercator map

The transverse Mercator can also be used to generate a global map--the equivalent of the 360o Mercator map. Using the command

    pscoast -R0/360/-80/80 -JT-30/-45/3.5i -B30g15/15g15WSne -Dc -A2000 -G0 -P >! GMT_TM.ps

we made the map illustrated in Figure 5.20. Note that when a world map is given (indicated by -R 0/360/s/n), the arguments are interpreted to mean oblique degrees, i.e., the 360o range is understood to mean the extent of the plot along the central meridian, while the ``south'' and ``north'' values represent how far from the central longitude we want the plot to extend. These values correspond to latitudes in the regular Mercator projection and must therefore be less than 90 degrees.

Figure 5.20: A global Transverse Mercator map

Next: Universal Transverse Mercator UTM Up: Cylindrical Projections Previous: Mercator Projection (-–Jm -JM)