User:Jcreer/Direction Conventions and Conversions

From XMS Wiki
< User:Jcreer
Revision as of 19:44, 9 December 2021 by Jcreer (talk | contribs)
Jump to navigationJump to search

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) |align="center"| 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)