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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
Hi Heiko, The only difference between the behaviour of ncWMS and THREDDS in this respect is that ncWMS will automatically scan each dataset and deduce a "sensible" colour scale range for each variable, then save this in the config file ($HOME/.ncWMS/config.xml). THREDDS has no such background process for scanning datasets (at the moment), so you have to enter this information manually in wmsConfig.xml. (You can use THREDDS' built-in Godiva2 client to help you work out sensible defaults if you like.) Both of these mechanisms set the *default* colour scale range for each variable. This is used if the COLORSCALERANGE parameter is omitted, and hence allows backward-compatibility with standard WMS clients. An "auto" colour scale range is quite different, and sets the scale range on a per-image basis. As you say, this isn't particularly useful except for quick-looks and debugging. See http://www.resc.rdg.ac.uk/trac/ncWMS/wiki/WmsExtensions for full details of the COLORSCALERANGE parameter in ncWMS. THREDDS behaves identically, except from the point of view of configuration, as described above. I know this is a little confusing - sorry about this. If you configure your colour scale ranges manually (sorry) in wmsConfig.xml your external WMS users should be able to access your images without a problem. (One day we might be able to port the ncWMS dataset-scanning mechanism to THREDDS, but we're concerned about performance and scalability. THREDDS servers can have a *lot* of datasets.) Hope this helps, Jon -----Original Message----- From: Heiko Klein [mailto:Heiko.Klein@xxxxxx] Sent: 21 September 2010 13:21 To: Jon Blower Cc: thredds@xxxxxxxxxxxxxxxx Subject: Re: Re-enabling a auto-scaling defaultColorScaleRange in ncWMS The method you implemented before you added the defaultColorScaleRange parameter in ncWMS was different from what you describe here. I'm quite sure that all images had the same scale and the values where adapted to the data-values within the file, i.e. for sea-ice concentration data, I got a scale between -5% - 105%. This was much better than what I get currently with the default -50 - 50. Seen from a performance point of you, it makes sense that an auto-colorrange tries to adjust the scale per image-data - but in the tiled WMS world, this doesn't make any sense, and if you plot a scale, you will need to decide what data to scale to, since no region is selected at all. And since the COLORSCALERANGE is a ncWMS extension, it is difficult for a general purpose wms-client to adapt to it. With the new ncWMS in 4.2, we will need to adapt our client to make use of these extensions to get useful pictures. Those producing the data are partly external users, and have only very limited rights, and definitely no administrative rights to configure the wmsConfig. Best regards, Heiko On 2010-09-21 12:49, Jon Blower wrote: > Hi Heiko, > > The problem with colorscalerange=auto is that the scale range is > automatically chosen *for each image*. The purpose of setting values in > the wmsConfig.xml is to ensure that each image from the same variable > gets the same colour scale for consistency with the legend and between > tiles in tiling clients. > > You can still use the URL parameter&COLORSCALERANGE=auto if you want > your image to be automatically contrast-stretched, but beware that the > image won't match the legend. > > Does this make sense? > > Cheers, Jon > > -----Original Message----- > From: Heiko Klein [mailto:Heiko.Klein@xxxxxx] > Sent: 21 September 2010 09:04 > To: thredds@xxxxxxxxxxxxxxxx > Cc: Jonathan Blower > Subject: Re-enabling a auto-scaling defaultColorScaleRange in ncWMS > > I upgraded to a snapshot of thredds 4.2 and I have seen the new > configuration options to ncWMS. In particular, the > defaultColorScaleRange seems to be new. > > I liked the old auto-colorScaleRange which determined the max and min > value from the datasets. Is this option still available within the > wmsConfig.xml file? I tried > <defaultColorScaleRange>auto</defaultColorScaleRange> and it didn't > work. > > Best regards, > > Heiko -- Dr. Heiko Klein Tel. + 47 22 96 32 58 Development Section / IT Department Fax. + 47 22 69 63 55 Norwegian Meteorological Institute http://www.met.no P.O. Box 43 Blindern 0313 Oslo NORWAY
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