[thredds] TDS WMS very slow for curvilinear grids (revisited)

• To: THREDDS community <thredds@xxxxxxxxxxxxxxxx>, <support-thredds@xxxxxxxxxxxxxxxx>
• Subject: [thredds] TDS WMS very slow for curvilinear grids (revisited)
• From: "Signell, Richard" <rsignell@xxxxxxxx>
• Date: Mon, 1 Apr 2013 08:03:01 -0400

THREDDS folks,

The issue of very slow TDS WMS for curvilinear grids game up again in
the ncWMS mailing list, and so I thought I would raise it here again,
since the current implementation is truly unworkable for any
reasonable size curvilinear grid.

As an example, if one tries to browse "potential temperature"  from
this USGS COAWST Forecast Model (a 900x400 curvilinear grid):

http://geoport.whoi.edu/thredds/catalog/coawst_4/use/fmrc/catalog.html?dataset=coawst_4/use/fmrc/coawst_4_use_best.ncd

using Godiva2, it takes about 20 seconds before the data set appears,
another 20 seconds to show the variable list, and then it takes
several *minutes* to produce a single temperature image.

Looking at the TDS threddsServlet.log, I can see that there are a
bunch of WMS requests for 256x256 tiles, to create a ~500x500 browse
window in Godiva 2.

And even a single test image request takes longer than 20 seconds.
http://geoport.whoi.edu/thredds/wms/coawst_4/use/fmrc/coawst_4_use_best.ncd?LAYERS=temp&ELEVATION=-0.03125&TIME=2013-04-01T00%3A00%3A00.000Z&TRANSPARENT=true&STYLES=boxfill%2Frainbow&CRS=EPSG%3A4326&COLORSCALERANGE=10%2C30&NUMCOLORBANDS=64&LOGSCALE=false&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&FORMAT=image%2Fpng&SRS=EPSG%3A4326&BBOX=-101.74989476701,11.888467352229,-53.253084362467,48.463925392208&WIDTH=512&HEIGHT=512

Why so long? If I drop the OPeNDAP URL for this dataset into ToolsUI
and use the Grid Viewer, it takes just a few seconds to plot the
temperature field.


Thanks,
Rich
-- 
Dr. Richard P. Signell   (508) 457-2229
USGS, 384 Woods Hole Rd.
Woods Hole, MA 02543-1598