User:Jcreer/Direction Conventions and Conversions

SMS supports the following direction conventions:

Cartesian:: Add definition

Meteorologic: Add definition

Oceanographic: Add definition

Shore Normal: "TO" convention based on a Theta(grid) which defines the grid orientation relative to the positive X axis (CCW direction). So:

Theta(grid)	Direction of I axis
0	East
90	North
180	West
270	South

For a shore normal grid, the direction angle is interpreted as relative to the I axis with CCW as positive. Therefore, if Theta(grid) is 0 degrees (I axis aligned with X axis) then:

                   0                        To the east
                 45                        To the north east
                -45                        To the south east

When SMS converts from one convention to another the conversions always goes through Cartesian. For example, to convert from Oceanographic to Meteorologic, SMS converts from Oceanographic to Cartesian, and then from Cartesian to Meteorologic.

The conversions that are:

Cartesian = 90 - Oceanographic

Cartesian = 270.0 - Meteorologic

Cartesian = ShoreNormal + GridOrientation

Meteorologic = 270.0 - Cartesian (add or subtract 360 if out of range)

ShoreNormal = Cartesian - GridOrientation (add or subtract 360 if out of range)

Oceanographic = 90.0 - Cartesian (add or subtract 360 if out of range)