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<font face="Comic Sans MS" size="3">Could the barb class be built up from primitives, stem anddifferent flags on the tail, based on the numbers passed in. Basically you would be writing the barb symbol out for each label location needed, instead of sampling from a list of many? Just use a max/min thresholding to decide when the symbol has something added to it or not. Still a bit laborious to setup, but I think it gets you there.</font> </p>
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<font face="Comic Sans MS" size="3">bobb</font> </p>
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>>> Brent Fraser <bfraser@geoanalytic.com> wrote:<br> </p>
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     At FOSS4G I was struck by the number of presentations involving<br>weather data and time series display.  Maybe I noticed because I have a<br>need to render wind velocity in KML, and while I haven't settled on<br>mapserver to do the rendering I've been wondering how to render wind<br>barb symbols (see attached graphics) efficiently.<br><br>   One problem is the source data: the magnitude is in one raster file<br>(GRIB format, float64)  and the direction in another.  GDAL's OGR<br>library will read the GRIB files, but I don't know of any way to use two<br>rasters to define a vector layer.  I think there is some work going on<br>with respect to displaying vector field data in mapserver, so maybe this<br>will be solved by that work.  Otherwise pre-processing the two rasters<br>into a point datasource containing lon,lat,speed,direction attributes<br>may be the way to go.<br><br>   The other issue of wind barb symbol rendering may have to be solved<br>by hand constructing a barb for 0 knots, 5 knots, etc (50-ish symbols?)<br>, and having 50-ish corresponding classes (this could be a performance<br>problem for mapserver).  But I'm open to better ideas...  SLD?  HTTP/CGI<br>request?, something like one class of:<br><br>   CLASS<br>     STYLE<br>       GEOMTRANSFORM "start"<br>       COLOR 0 255 0<br>       SIZE 15.0<br>       SYMBOL "http://localhost/symbolgen?[speed]"<br>       ANGLE [direction]<br>     END<br>   END<br><br>   but likely the cost of getting the symbol would be greater that<br>creating 50 separate class objects.<br><br>And for those interested in mapping and graphing weather data, have a<br>look at <a href="http://www.ncl.ucar.edu/Applications/">http://www.ncl.ucar.edu/Applications/</a><br>especially <a href="http://www.ncl.ucar.edu/Applications/barb.shtml">http://www.ncl.ucar.edu/Applications/barb.shtml</a><br><br>--<br>Best Regards,<br>Brent Fraser<br><br>
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