[QGIS-trac] [Quantum GIS] #1102: Digitizing over an image hides image with white mask

[Quantum GIS]

#1102: Digitizing over an image hides image with white mask
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   Reporter:  nedhorning                        |              Owner:  nobody
       Type:  bug                               |             Status:  new   
   Priority:  major: does not work as expected  |          Milestone:        
  Component:  Digitising                        |            Version:  HEAD  
   Keywords:  image digitiing                   |   Platform_version:        
   Platform:  Windows                           |           Must_fix:  No    
Status_info:  0                                 |  
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 There is a problem when digitizing a polygon on top of a raster image.
 When digitizing a polygon layer on top of an image the area defined by the
 bounding box of the polygon verticies (or any point covered by the cursor)
 becomes an opaque white which hides the underlaying image. This is a
 problem for us since we are trying to digitize features that can be seen
 in a satellite image.

 After loading the satellite image and doing an enhancement we create a new
 polygon vector file and place it on top of the raster image. We then make
 it editable and then start drawing a polygon. As we draw, the image area
 under the bounding box of the polygon becomes white effectively creating a
 mask that hides the image. The white mask disappears after the polygon is
 closed. We can “erase” the white mask by refreshing the screen (using ctrl
 +R) but it reappears as soon as the cursor is moved. If we move the vector
 layer under the raster layer then the digitizing works fine with no white
 mask but after the polygon is finished it cannot be seen since the vector
 layer is under the raster layer.

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Ticket URL: <https://trac.osgeo.org/qgis/ticket/1102>
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