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.