Projection parameters

A map projection by itself isn't enough to define a projected coordinate system. You can state that a dataset is in Transverse Mercator, but that's not enough information. Where is the center of the projection? Was a scale factor used? Without knowing the exact values for the projection parameters, the dataset can't be reprojected.

Learn more about the Transverse Mercator projection.

You can also get some idea of the amount of distortion the projection has added to the data. If you're interested in Australia but you know that a dataset's projection is centered at 0,0, the intersection of the equator and the Greenwich prime meridian, you might want to think about changing the center of the projection.

Each map projection has a set of parameters that you must define. The parameters specify the origin and customize a projection for your area of interest. Angular parameters use the geographic coordinate system units, while linear parameters use the projected coordinate system units.

Linear parameters

False easting is a linear value applied to the origin of the x-coordinates. False northing is a linear value applied to the origin of the y-coordinates.

False easting and northing values are usually applied to ensure that all x- and y-values are positive. You can also use the false easting and northing parameters to reduce the range of the x- or y-coordinate values. For example, if you know all y-values are greater than 5,000,000 meters, you could apply a false northing of -5,000,000.

Height defines the point of perspective above the surface of the sphere or spheroid for the vertical Nnear-side perspective projection.

Angular parameters

For other conic cases, the y-coordinate origin is defined by the latitude of origin parameter.

The four parameters above are used with the two-point equidistant and Hotine Oblique Mercator projections. They specify two geographic points that define the central axis of a projection.

Learn more about the two-point equidistant projection.

Unitless parameters

Learn more about the Krovak projection.

Related Topics

3/3/2014