[QGIS-trac] [Quantum GIS] #1727: Support Multiple Rules per Style for a Layer

[Quantum GIS]

#1727: Support Multiple Rules per Style for a Layer
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   Reporter:  springmeyer                      |              Owner:  nobody
       Type:  enhancement                      |             Status:  new   
   Priority:  minor: annoyance or enhancement  |          Milestone:        
  Component:  Build/Install                    |            Version:  HEAD  
   Keywords:                                   |   Platform_version:        
   Platform:  Debian                           |           Must_fix:  No    
Status_info:  0                                |  
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 It appears that currently QGIS can only apply one style (or set of
 'symbols') to a layer (one2one relationship). But to support proper scale
 dependent rendering of layers it will be necessary to allow multiple rules
 (with their own min/max visibility) to contain sets of symbols and be
 applied to a single layer (many2one between style rules-> layer).

 This is essentially what all the major web rendering engines support, and
 well described by the SLD spec (see request for SLD support in #1167).

 The challenge here is not writing the code to process and render multiple
 rules, but in designing and supporting a good user interface to expose the
 ability to edit styles in this way. It is notable that even the new GeoExt
 Styler does not yet support this (but has it as a first item on the
 roadmap as of June 10,2008):

 From http://projects.opengeo.org/styler :
 '''
 Symbolizer improvements

 In order to support features like roads with outlines, we need the ability
 to define more than one symbolizer on a rule. Right now there is an
 assumption that each rule only has one symbolizer. This is not a
 constraint of SLD, just on what we've built thus far. The first release of
 Styler also does not support all the potential options for SLD strokes and
 labels. These should be accessible in the UI, to give users full control
 over their output.

 Design proposal: Symbolizers
 Implementation details:
 http://projects.opengeo.org/styler/wiki/Symbolizers and
 http://projects.opengeo.org/styler/ticket/39
 '''

 Nevertheless this is an essential feature, that if implemented will bring
 QGIS to a high level of usefulness for creating mapping styles for web
 applications.

-- 
Ticket URL: <http://trac.osgeo.org/qgis/ticket/1727>
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