[mapserver-users] Rendering weather data

[Paul Ramsey]

Once you have vectors, the classic trick I've seen for doing the barbs
is to do math to map the windspeed into an appropriate char() value
and store the barbs as TTF font entries. So you only end up with one
class, and the barb is an appropriately rotated label.

P.

On Tue, Sep 27, 2011 at 10:31 AM, Brent Fraser <bfraser at geoanalytic.com> wrote:
>    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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