Bug report #13296: topology checker misleading errors - QGIS Application - QGIS Issue Tracking

Bug report #13296

topology checker misleading errors

Added by Giovanni Manghi about 9 years ago. Updated over 5 years ago.

Status:	Closed
Priority:	Normal
Assignee:	-
Category:	C++ plugins/Topology checker
Affected QGIS version:	2.8.3	Regression?:	No
Operating System:		Easy fix?:	No
Pull Request or Patch supplied:	No	Resolution:	end of life
Crashes QGIS or corrupts data:	No	Copied to github as #:	21354

Description

When digitizing adjacent polygons using the "avoid intersection" rule, is easy enough at some point (especially if the layer is reprojected) to get gaps or overlapped areas... at least the topology checker says so. A further check, with GRASS, seems to exclude this problems, as holes (gaps) and overlapping areas are not detected.

History

#1 Updated by Thomas Nogatz over 8 years ago

Could you describe please how you did check the layer with GRASS?

#2 Updated by Giovanni Manghi over 8 years ago

Thomas Nogatz wrote:

Could you describe please how you did check the layer with GRASS?

you have to import your vector into a GRASS mapset/location. You can do it using native GRASS or you can also use the QGIS/GRASS plugin (also to create a new mapset/location). The import module is v.in.ogr and you should use in first place without using any snapping option. After importing the vector you may end with up to 3 different GRASS layers: 0, 1, 2.

1 is the "normal" layer as you would expect
0 is a layer with polygons representing the holes/rings/spaces in the original layer
2 is a layer with polygons representing the overlapped areas in the original layer

if after the import you end up with just the 1 layer, then your original layers has no holes/rings/spaces and no overlapping areas.