[QGIS-trac] [Quantum GIS] #3736: Repeated QgsGrassRasterProvider::identify slow

[Quantum GIS]

#3736: Repeated QgsGrassRasterProvider::identify slow
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   Reporter:  rblazek           |              Owner:  rblazek      
       Type:  bug               |             Status:  new          
   Priority:  minor: annoyance  |          Milestone:  Version 1.7.0
  Component:  GRASS             |            Version:  Trunk        
   Keywords:                    |   Platform_version:               
   Platform:  All               |           Must_fix:  Yes          
Status_info:  0                 |  
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 In the GRASS provider, I have followed the recommended use of GRASS in
 applications, that means, if a value on certain pixel is requested, it
 runs GRASS module (executable) with coordinates as parameter and
 receives a value from stdout.

 If a user moves cursor over the whole map, it may run the GRASS module
 some 1000 times on medium size screen. If there are 10 maps open in
 QGIS, it starts 10000 executables in about 1 second. That is probably
 a bit slow.

 We could add some delay in the Value tool plugin to avoid too many
 requests, but that is not solution if the values have to be logged
 somehow, for example to draw a chart.

 It seems that instead of running the GRASS module each time, we have
 to keep it running and send coordinates to the module via stdin.

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/3736>
Quantum GIS <http://qgis.org>
Quantum GIS is an Open Source GIS viewer/editor supporting OGR, PostGIS, and GRASS formats