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)

<-- (Note: A definition for the first three can be taken from :

           https://www.xmswiki.com/wiki/Template:Angle_Convention)

(Note: It would also be good to have some images to illustrate. You can see an idea of this by doing the following:

 - create a new spectral coverage
 - create a point in the coverage
 - double click on the point to bring up the spectral energy dialog
 - click "Create Grid" and click OK two times to get a grid
 - click "Generate Spectra" to bring up the Generate Spectra grid
 - enter 0, 25, 1, 1 in the parameters table
    At this point the picture in the upper right corner of the dialog displays the direction. You can change the convention to see samples of the images I am talking about)

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