[GRASS-user] v.clean Failed to build area

Wed May 2 07:28:21 PDT 2018

My best guess is each line is creating a close polyline - which is why  
the islands do not have duplicate points.

We wrote a program to run though each line, identify the location each  
line begins to backtrack, then break and remove the remaining points.   
Unfortunately, some of the contours do not start and stop at the edge  
of the DEM, but rather have beginning nodes many points within the  
DEM.  Anything on the "back side" of the node is dropped.

Heidi Ochis
Computer Terrain Mapping, Inc
420 21st Ave, Suite 114
Longmont, CO 80501
303-444-1670
hiho at ctmap.com

On May 2, 2018, at 12:32 AM, Markus Metz wrote:

Hi Peter,

On Tue, May 1, 2018 at 11:33 PM, Peter Tittmann <ptittmann at gmail.com>  
wrote:
 >
 > Hi Markus,
 >
 > I'm ashamed to admit that I hacked my way into fixing this problem  
by exporting the vector dataset using `v.out.ogr` to a geopackage then  
importing it. The cleaning tools in v.in.ogr seemed to solve my  
problem..

the reason why this works is that these incorrect boundaries are not  
exported. When re-importing, you will get a clean vector but some of  
the original areas are gone. If you still want to find out what went  
wrong where, you would need to find out where these incorrect  
boundaries first appeared in the processing steps of your original  
vector.

Markus M

 >
 > Very clumsy, but it worked.
 >
 > Thank you!
 >
 > Peter
 >
 > On Fri, Apr 27, 2018 at 11:51 AM, Markus Metz <markus.metz.giswork at gmail.com 
 > wrote:
 >>
 >> [ please keep this on the GRASS mailing list ]
 >>
 >> On Fri, Apr 27, 2018 at 6:43 PM, Peter Tittmann  
<ptittmann at gmail.com> wrote:
 >> >
 >> > Hi Markus,
 >> >
 >> > grass72 -v
 >> > GRASS GIS 7.2.2
 >>
 >> This is already the latest 7.2 release. You might try GRASS 7.4.
 >>
 >> >
 >> > i will try to figure out how to get the latest release up and  
running. If you have any suggestions for fixing the boundaries, that  
would be great.
 >>
 >> If upgrading to the latest GRASS 7.4 release does not help, I  
would need the data for testing to find out why removing small areas  
fails. If the vector has been imported from an external datasource  
without modification of the geometries inside GRASS, this version  
would be preferable. Otherwise the history of  
plot_pa_with_lidar at project_area would be helpful (v.info -h).
 >>
 >> Markus M
 >> >
 >> > Peter
 >> >
 >> > On Thu, Apr 26, 2018 at 11:19 PM, Markus Metz <markus.metz.giswork at gmail.com 
 > wrote:
 >> >>
 >> >>
 >> >>
 >> >> On Fri, Apr 27, 2018 at 1:37 AM, Peter Tittmann <ptittmann at gmail.com 
 > wrote:
 >> >> >
 >> >> > Hi,
 >> >> >
 >> >> > I am attempting to use the `rmarea` tool in v.clean with a  
threshold of ~ 1000 sq meters.
 >> >> >
 >> >> [...]
 >> >>
 >> >> >
 >> >> >  I am getting a rather cryptic message ‘Failed to build area’.
 >> >> >
 >> >> > > v.clean -c --overwrite --verbose  
input=plot_pa_with_lidar at project_area output=plot_pa_rmarea  
tool=rmarea threshold=1017.2
 >> >> > --------------------------------------------------
 >> >> > Tool: Threshold
 >> >> > Remove small areas: 1017.2
 >> >> > --------------------------------------------------
 >> >> > WARNING: Vector map <plot_pa_rmarea> already exists and will  
be overwritten
 >> >> > Using native format
 >> >> > Copying features...
 >> >> >  100%
 >> >> > Rebuilding parts of topology...
 >> >> > Building topology for vector map  
<plot_pa_rmarea at project_area>...
 >> >> > Registering primitives...
 >> >> > 1720636 primitives registered
 >> >> > 3439992 vertices registered
 >> >> > Building areas...
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> > WARNING: Area of size = 0.0 ignored
 >> >> >  100%
 >> >> > 499671 areas built
 >> >> > 6004 isles built
 >> >> > Attaching islands...
 >> >> >  100%
 >> >> > Attaching centroids...
 >> >> >  100%
 >> >> > Topology was built
 >> >> > Number of nodes: 728615
 >> >> > Number of primitives: 1720636
 >> >> > Number of points: 0
 >> >> > Number of lines: 0
 >> >> > Number of boundaries: 1222309
 >> >> > Number of centroids: 498327
 >> >> > Number of areas: 499671
 >> >> > Number of isles: 6004
 >> >> > WARNING: Number of incorrect boundaries: 9
 >> >> > WARNING: Number of duplicate centroids: 14
 >> >> > --------------------------------------------------
 >> >> > Tool: Remove small areas
 >> >> > ERROR: Failed to build new area
 >> >>
 >> >> I guess the problem are these 9 incorrect boundaries. Which  
GRASS version are you using? Can you try again with the latest release  
in case you are not using the latest release?
 >> >>
 >> >> Markus M
 >> >
 >> >
 >
 >
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