[mapserver-users] Rendering weather data

[Brent Fraser]

     At FOSS4G I was struck by the number of presentations involving 
weather data and time series display.  Maybe I noticed because I have a 
need to render wind velocity in KML, and while I haven't settled on 
mapserver to do the rendering I've been wondering how to render wind 
barb symbols (see attached graphics) efficiently.

   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

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