[mapserver-users] Rendering weather data

[Brent Fraser]

Bob,

   Maybe.  I had considered some kind of programmed CGI-based URL 
function to create the wind barb (hence the interest in UCAR's NCL), but 
I don't think mapserver has the capability to use a URL as a symbol 
reference (would be a nice enhancement).

    I don't know how to procedurally add components within a map file 
using CLASS, STYLE, and SYMBOL.  Could be done with MapScript I suppose....

Best Regards,
Brent Fraser


On 9/27/2011 11:54 AM, Bob Basques wrote:
>
> 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.
>
>
> bobb
>
>
>
>
>
>
> >>> 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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