[mapserver-users] Accessing raster cell values

[Andrew Mason]

Hello List,

This question may be a general newbie GIS question and not solely  
related to Mapserver, so apologies if I'm posting to the wrong place.

I am serving a GeoTiff via Mapserver using WMS, and displaying it  
using OpenLayers, so far so good.
I need to be able to click on a point on the map and display the  
value held within that particular Raster cell.
Can anyone suggest what mechanism I should use for this? WCS looks  
like it might be the thing I need, but I'm having difficulty finding  
much in the way of examples and instructions.
I've followed what examples there are and all I can get Mapserver to  
return using WCS, is a Geotiff with every pixel set to zero.
So I've obviously not got it working correctly, and even if it were  
I'm not sure how to get the information I need out of the returned  
Geotiff when my client is OpenLayers.

Can anyone suggest a way to access a raster's values when it is  
served by Mapserver and viewed using OpenLayers?

Thank you

Andrew Mason