How to calculate Azimuth from Angle in map file?

[Richard Greenwood]

On 8/20/07, Brent Fraser <bfraser at geoanalytic.com> wrote:
> Mapservites,
>
>     I've got shapefiles with angle values (0 degrees =
> positive X axis,  increasing counter clockwise) but
> Mapserver uses azimuths ( 0 = positive Y axis, increasing
> clockwise) when rotating symbols.
>
>   Is there any way to calculate azimuth from angle in the
> map file?  I don't want to modify the dbf portions of the
> shapefile if I don't have to; there's 13,000 of them, and I
> may get updates so maintenance could be a pain.
>
>   It would be nice if I could do something like:
>
>       STYLE
>        SYMBOL "pt_Building"
>        ANGLE (90 - [angle])    # this doesn't work, so don't
> try it!
>        COLOR        80 80 80
>       END
>
> Any ideas?
>
> Brent Fraser
> GeoAnalytic Inc.
> Calgary, Alberta

Not sure if this will work in a map file, but the formula I use to
convert "mathematical" angles to azimuths is:

azimuth = (450-m) - int( (450-m) / 360 ) * 360

where "m" is the "mathematical" angle.

-- 
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com