[QGIS-trac] [Quantum GIS] #2989: improve reading of DWG to equal DNG functionality

[Quantum GIS]

#2989: improve reading of DWG to equal DNG functionality
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   Reporter:  dcarreira                         |              Owner:  jef          
       Type:  enhancement                       |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.6.0
  Component:  Vectors                           |            Version:               
   Keywords:  dwg, dgn, cad                     |   Platform_version:               
   Platform:  Windows                           |           Must_fix:  No           
Status_info:  0                                 |  
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 QGIS already reads DGN files (at least v7), mixing all geometry types in
 one single layer.


 One can then filter each geometry type by querying the dgn layer. For
 example, to filter all lines you can use this query:
 [[BR]]

 "Type"  IN  ('3','4','12','14','16','15')
 [[BR]]

 The layer will have only lines after this query is applyed. To know which
 type codes correspond to each geometry type you can lookup on certain web
 pages, like:[[BR]]

 http://www.gdal.org/ogr/drv_dgn.html
 [[BR]]
 http://www.gisdevelopment.net/technology/gis/techgi0011.htm
  [[BR]]
 I attached an example dgn file where you can exercise this kind of
 filtering.
 [[BR]]

 You can also by this means, get all text elements:[[BR]]
 "Type" = '17'[[BR]]

 Note that QGIS does not reset the symbology according to the query
 results. So the default line symbology is kept and nothing is visible
 since the layer now holds only points. To workaround this limitation, you
 have only to change the symbology type to "Categorized", and then back to
 "Single Symbol". QGIS will pick up on the geometry type and propose the
 default point symbol. At this stage you can see the text points.

 Since all DGN attributes that are captured by OGR are available to QGIS
 you can also show the texts by labeling the points.

 Finally, you can export each geometry type to separate shapefiles. Later
 on, you can work these shapefiles and further filter elements by level
 (the dgn's equivalent to dwg's layers).

 This process allows QGIS to work with CAD data directly, without requiring
 external tools, like ogr2ogr. Extending this support to dwg would be a
 breakthrough!

-- 
Ticket URL: <https://trac.osgeo.org/qgis/ticket/2989>
Quantum GIS <http://qgis.org>
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