Re: [thredds] 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,


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

Best regards,


Dr. Heiko Klein                              Tel. + 47 22 96 32 58
Development Section / IT Department          Fax. + 47 22 69 63 55
Norwegian Meteorological Institute 
P.O. Box 43 Blindern  0313 Oslo NORWAY

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