One problem is the source data: the magnitude is in one raster file (GRIB format, float64) and the direction in another. GDAL's OGR library will read the GRIB files, but I don't know of any way to use two rasters to define a vector layer. I think there is some work going on with respect to displaying vector field data in mapserver, so maybe this will be solved by that work. Otherwise pre-processing the two rasters into a point datasource containing lon,lat,speed,direction attributes may be the way to go.
The other issue of wind barb symbol rendering may have to be solved by hand constructing a barb for 0 knots, 5 knots, etc (50-ish symbols?) , and having 50-ish corresponding classes (this could be a performance problem for mapserver). But I'm open to better ideas... SLD? HTTP/CGI request?, something like one class of:
CLASS
STYLE
GEOMTRANSFORM "start"
COLOR 0 255 0
SIZE 15.0
SYMBOL "http://localhost/symbolgen?[speed]";
ANGLE [direction]
END
END
but likely the cost of getting the symbol would be greater that
creating 50 separate class objects.
And for those interested in mapping and graphing weather data, have a look at http://www.ncl.ucar.edu/Applications/
especially http://www.ncl.ucar.edu/Applications/barb.shtml -- Best Regards, Brent Fraser
<<attachment: Wind_barbs.gif>>
<<attachment: windbarbs.png>>
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