Transparency based on classification, possible?

[Fawcett, David]

I was thinking about this a little bit.  There is a way that you could do this, but it may be a little ugly.  

If you only want to do this for one (or a few) layer and you don't need to break your data up into too many classes of varied transparency.  

You could create a layer for each desired classification, have one class in each layer and set an expression in that class to only show the features that you want to assign a particular level of transparency to.  You would then set transparency at the layer level.  Also, remember that transparency behaves more like a property that would be called opacity.  A transparency of 20 is more 'see through' than a transparency of 80.  

Legends and queries might be a little funky with this arrangement, but you should be able to work around them.  

David.


-----Original Message-----
From: Fawcett, David
Sent: Fri 9/8/2006 4:44 PM
To: 'Hong'; MAPSERVER-USERS at LISTS.UMN.EDU
Subject: RE: [UMN_MAPSERVER-USERS] Transparency based on classification, possible?
 
No.  

Transparency is set at the layer level.  Take a look at: http://mapserver.gis.umn.edu/docs/reference/mapfile/layer

If you want to use URL variable substitution, you could probably change the transparency of the LAYER on the fly, but not at the class level.  

David.

-----Original Message-----
From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On Behalf Of Hong
Sent: Friday, September 08, 2006 4:37 PM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: [UMN_MAPSERVER-USERS] Transparency based on classification, possible?


Hello,

Is it possible to set the transparency of layer symbolization based on the classification? Something similar to the effect of:

LAYER
	...
	CLASS
		EXPRESSION "expr0"
		TRANSPARENCY 50
	END CLASS
	CLASS
		EXPRESSION "expr1"
		TRANSPARENCY 70
	END CLASS
END LAYER

Thanks.