# Plot Domains

**MAP PROJECTIONS**

**ps**- Polar Stereographic

This projection is developed by mapping latitude and longitude to a plane. This results in a polar coordinate system in the sense that longitudes map to angles and latitudes map to radius. For a northern hemisphere projection, the projection plane is defined as a flat surface parallel to the equator and passing through 60 North. A point on the earth's surface is projected onto the plane by passing a line from the south pole through the point on the earths surface to the plane. The resulting Cartesian coordinate system has 0,0 as either the north or south pole. The plon defines the longitude which maps to the negative Y axis. This projection is recommended for polar and middle latitude plots and for hemispheric plots centered on the north or south pole. The formula is:

alpha is the latitude of interest, alpha-t is the true latitude which is 60, theta is the longitude, theta-p is the projection longitude, C is the map factor which is 1.866 (true at 60), rho is the radius of the earth in 100s of km (63.71).**ll**- Latitude-Longitude

This is the simplest of the projections where longitude is mapped to x and latitude to y. This is good for tropical plots where distances are preserved and can be used elsewhere if the appropriate dx and dy are picked to preserve distances. This can be done by using dy = dx * cos(clat). The formula is:

where alpha is the latitude of interest, theta is the longitude, theta-p is the projection longitude.**lc**- Lambert Conformal

This is very similar to polar stereographic except that the projection plane is a cone fitted over the earth centered over a pole and passing through 30 and 60 degrees of latitude. The projection is still made by passing a line from the opposite pole through the point on the earth's surface to the plane. This projection is very good for middle latitude plots. The formula is:

alpha is the latitude of interest, alpha1 and alpha2 are the true latitudes which are 30 and 60, theta is the longitude, theta-p is the projection longitude, C is the map factor, rho is the radius of the earth in 100s of km (63.71).**me**- Mercator

This is a cylindrical projection in that a cylinder is placed over the earth and the point on the earth is projected on the cylinder by passing a line from the center of the earth through the point on the earth to the cylinder. This projection attempts to preserve relative x and y distances at a particular latitude but tends to enlarge regions near the poles. This is a good projection for tropical and middle latitude plots. The formula is:

where alpha is the latitude of interest, theta is the longitude, theta-p is the projection longitude, rho is the radius of the earth in 100s of km (63.71).**sat**- Satellite

This projection assumes a satellite located at some radius from the earth projects a line through a specific point on the earth's surface to a plane placed perpendicular to a line from the satellite to the center of the earth. As of this version, this projection is set up only for geostationary satellites. The longitude over which the satellite is located is defined by plon. The formula is:

alpha is the latitude of interest, theta is the longitude, theta-p is the projection longitude, C is the map factor, rho-E is the radius of the earth in 100s of km (63.71), rho-S is the radius of the satellite in 100s of km (421.61).**NON-MAP PROJECTIONS****xy**- XY

This projection assumes a domain which has a standard Cartesian coordinate setup.**pix**- Pixel

This projection assumes a domain which has coordinates resembling those of a display with Y increasing down.**xlogp**- X log P

This projection assumes a domain which has coordinates resembling those of a upper air cross-section with Y increasing down in a logarithmic scale.**cat**- Category

This projection assumes a domain which has category based coordinate system where X is the category number.**NON-PROJECTIONS**

These projections only exist to allow labelling of various plots.**therm**- Thermodynamic plot**hodo**- Hodograph plot**vert**- Vertical cross-section plot**miss**- No projection