# CPP Coordinate System

This is the approved revision of this page, as well as being the most recent.

A CPP (la carte parallelogrammatique projection, also called equirectangular projection or equidistant cylindrical projection) system is a local system. The projection maps meridians to vertical straight lines of constant spacing (for meridional intervals of constant spacing), and circles of latitude to horizontal straight lines of constant spacing (for constant intervals of parallels). The projection is neither equal area nor conformal. The CPP system has become a standard for global raster datasets, such as Celestia and NASA World Wind, because of the particularly simple relationship between the position of an image pixel on the map and its corresponding geographic location on Earth.

The origin of the system must be defined in latitude/longitude decimal degrees.

The conversion from of a point from latitude/longitude to CPP is:

The conversion of a point from CPP to latitude/longitude is:

${\displaystyle {\text{newpoint}}_{\text{longitude}}={\text{origin}}_{\text{longitude}}+{\frac {{\text{point}}_{x}}{R*\cos {\big (}{\text{origin}}_{\text{latitude}}{\big )}}}}$
${\displaystyle R=6378206.4m.}$ (Clarke 1866 major spheroid radius)