[thredds] LayerLimit

• To: "thredds@xxxxxxxxxxxxxxxx" <thredds@xxxxxxxxxxxxxxxx>
• Subject: [thredds] LayerLimit
• From: Gerben de Boer <Gerben.deBoer@xxxxxxxxxxx>
• Date: Wed, 25 Jun 2014 13:00:23 +0000

A TDS WMS GetMap request returns at most 1 WMS layer per request. If one 
requests more, by specifying a comma-separate list form layers= and styles=, 
TDS returns an error message

<ServiceExceptionReport xmlns="http://www.opengis.net/ogc"; 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; version="1.3.0" 
xsi:schemaLocation="http://www.opengis.net/ogc 
http://schemas.opengis.net/wms/1.3.0/exceptions_1_3_0.xsd";>
<ServiceException>
You may only create a map from 1 layer(s) at a time
</ServiceException>
</ServiceExceptionReport>

However, the WMS 1.3.0 standard prescribes that in this case TDS should 
explicitly mention a <LayerLimit> element in the GetCapabilities:

"The optional <LayerLimit> element in the service metadata is a positive 
integer indicating the maximum number of layers a client is permitted to 
include in a single GetMap request. If this element is absent, the server 
imposes no limit." (page 23, OpenGIS(r) Web Map Server Implementation 
Specification)

This means that THREDDS should add this element to the GetCapabilities 
(LayerLimit=1) (or return more maps to be OGC compliant).
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