[mapserver-users] Rendering weather data

[Norman Vine]

On Sep 27, 2011, at 2:03 PM, Paul Ramsey wrote:

> 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.

This might help
http://carocoops.org/bb/viewtopic.php?t=169


> 
> 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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>> 
>> 
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