# 3D Theory - UTM - Universal Transverse Mercator

A projective spatial reference frame employs a projection of the ellipsoid onto some simple surface such as a cone or a cylinder, for example, the Lambert Conformal Conic (LCC) or the Universal Transverse Mercator (UTM) projections.

Universal Transverse Mercator. One further required argument must be supplied for UTM in order to specify the zone number (1..60). This is given in the form "Z<n>", where <n> is the zone number. An optional argument of "S" may be supplied in order to specify that the coordinates are in the southern hemisphere (otherwise, northern hemisphere will be assumed). A further optional argument may be used to specify the ellipsoid using one of the ellipsoid codes that are defined here. If no ellipsoid is specified, then "WE" is assumed, i.e. the WGS84 ellipsoid. An optional "WGS84" string can be specified if you wish all elevations to relative to the WGS84 geoid, i.e. mean sea level otherwise, all elevations will be relative to the ellipsoid. An example spatial reference frame definition of this format is [ "UTM", "Z10", "S", "GD" ], for a southern hemisphere UTM spatial reference frame in zone 10 with all elevations being with respect to mean sea level.

### x3d coding

(<northing>, <easting>, <elevation>) or (<easting>, <northing>, <elevation>). The order of northing and easting is controlled by the geoSystem field. If "northing_first" is specified, the order is northing then easting. If "easting_first" is specified, the order is easting then northing. If neither is specified, "northing_first" is the default. Elevation is always specified third. Northings, eastings, and elevation are all given in units of metres. The zone of the coordinate, and whether it is in the southern hemisphere, are defined in the geoSystem string. Elevation is given with reference to the ellipsoid (the default) or the WGS84 geoid (if  the "WGS84" parameter is specified in the geoSystem field). For example, (4145173, 572227, 0) is the zone 10 northern hemisphere UTM coordinate for Menlo Park, California, USA.

Supported earth geoids

Code Name
WGS84 WGS84 geoid

See following diagram for the geographic extent of each UTM zone: UTM Grid Zones of the World