[OpenLayers-Users] What Makes a Layer "queryable"? (ref: WMSGetFeatureInfo())

[Bill Thoen]

Using OL over MapServer, if you pass a list of layers to 
WMSGetFeatureInfo() where one of them is not queryable, you get no 
results even for the ones that are queryable. What I'm wondering is what 
do I test in a layer to make sure it's queryable before I pass it to 
WMSGetFeatureInfo()? For example, if you forget to specify a template 
reference in your mapfile, then the layer cannot be queryed. I think it 
also must have metadata specified --wms_title and wms_srs, at least. And 
if you want to see the attributes you also need to specify the metadata 
element gml_include_items and set DUMP to TRUE. But I don't have 
mapscript working yet and I can't get into the mapfile from OpenLayers 
using JavaScript.

Or do you have to do something like test each layer at its centroid with 
WMSGetFeatureInfo() to see if it returns results from that layer and  
adjust what you're passing into OL accordingly? Or is there another, 
less kludgy approach that I've missed?

Thanks,
- Bill Thoen