[mapguide-trac] #251: Reduce server load, response time and transfer size, when using AJAX selections

[MapGuide Open Source]

#251: Reduce server load, response time and transfer size, when using AJAX
selections
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   Reporter:  ksgeograf          |       Owner:                                   
       Type:  enhancement        |      Status:  new                              
   Priority:  medium             |   Milestone:  1.3                              
  Component:  Rendering Service  |     Version:  1.2.0                            
   Severity:  major              |    Keywords:  overlay size speed selection ajax
External_id:                     |  
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 Currently the mapguide server operation GETDYNAMICOVERLAYIMAGE is used to
 render the map, when a selection is made.

 This requires that the server re-renders the image and transfers the whole
 image to the client.

 It would be a lot more efficient if the server only produced a transparent
 overlay image and returned that. My testing shows that it is possible to
 produce the desired image by a simple process:


 {{{
 1. Edit the MapDefinition xml, and set the alpha value of the background
 color to 0 (transparent).
 2. Show the map, having only one layer visible and selectable.
 3. Select the feature in the visible layer.
 4. Toggle the layer invisible in the legend.
 }}}

 The returned png is transparent and contains a nicely alpha blended
 selection overlay.

 A sample measuring indicates that the normal selection procedure requires
 350kb datatransfer and 1.2 seconds delay. The overlay-only version
 requires 7kb data and 300 ms.

 This can be implemented, either by a new operation :
 "GETDYNAMICOVERLAYSELECTION"
 or by an aditional parameter to GETDYNAMICOVERLAYIMAGE : "SELECTIONONLY".

 Eiter way, it should do the same as the current GETDYNAMICOVERLAYIMAGE
 but:

 {{{
 1. Ensure the background is transparent
 2. Not render any layers, only the final selection part
 }}}

-- 
Ticket URL: <http://trac.osgeo.org/mapguide/ticket/251>
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