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Bob,<br>
<br>
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).<br>
<br>
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....<br>
<br>
<pre class="moz-signature" cols="72">Best Regards,
Brent Fraser</pre>
<br>
On 9/27/2011 11:54 AM, Bob Basques wrote:
<blockquote cite="mid:4E81C783020000A80002E797@heckle" type="cite">
<p style="margin-bottom: 0; margin-top: 0"> <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>
<br>
<p style="margin-bottom: 0; margin-top: 0"> <font face="Comic
Sans MS" size="3">bobb</font> </p>
<br>
<br>
<br>
<p style="margin-bottom: 0; margin-top: 0"> <br>
<br>
>>> Brent Fraser <a class="moz-txt-link-rfc2396E" href="mailto:bfraser@geoanalytic.com"><bfraser@geoanalytic.com></a> wrote:<br>
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<p style="margin-bottom: 0; margin-top: 0"> 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 <a class="moz-txt-link-rfc2396E" href="http://localhost/symbolgen?[speed]">"http://localhost/symbolgen?[speed]"</a><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 moz-do-not-send="true"
href="http://www.ncl.ucar.edu/Applications/">http://www.ncl.ucar.edu/Applications/</a><br>
especially <a moz-do-not-send="true"
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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