[GRASS-user] areas with no centroid

GRASS GRASS user
1

After editing a map with wxgui I ended up with 39 areas and 38 centroids. How do I find and delete the area with no centroid?

I have tried many combinations of v.info, v.category, v.to.db, and visualizing with d.vect. If I use v.clean tool=rmarea with slowly increasing thresholds it gets rid of an area I want before it finds the one I don't so I don't think it's a sliver.

GRASS GIS 7.3.svn > v.info demo
  . . .
Number of points: 0 Number of centroids: 38 Number of lines: 0 Number of boundaries: 112
Number of areas: 39 Number of islands: 19
  . . .
GRASS GIS 7.3.svn > v.category demo op=report
Layer/table: 1/demo
type count min max
point 0 0 0
line 0 0 0
boundary 0 0 0
centroid 38 1 75
area 0 0 0
face 0 0 0
kernel 0 0 0
all 38 1 75

Thanks, Dave
--

2

Dave Roberts wrote

After editing a map with wxgui I ended up with 39 areas and 38
centroids. How do I find and delete the area with no centroid?

I have tried many combinations of v.info, v.category, v.to.db, and
visualizing with d.vect. If I use v.clean tool=rmarea with slowly
increasing thresholds it gets rid of an area I want before it finds the
one I don't so I don't think it's a sliver.

GRASS GIS 7.3.svn > v.info demo
  . . .
Number of points: 0 Number of centroids: 38
Number of lines: 0 Number of boundaries: 112
Number of areas: 39 Number of islands: 19
  . . .
GRASS GIS 7.3.svn > v.category demo op=report
Layer/table: 1/demo
type count min max
point 0 0 0
line 0 0 0
boundary 0 0 0
centroid 38 1 75
area 0 0 0
face 0 0 0
kernel 0 0 0
all 38 1 75

Thanks, Dave
--
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d. vect has following option :

cat: Display category numbers of features

try to display the cat info for the polygones to check where the centroid is
missing.

have then a look at v.extract and extract only these polygones you need.

HTH

-----
best regards
Helmut
--
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3

Hi Helmut,

    Thanks for the suggestion, but the area with no centroid doesn't have a cat. I think somehow I deleted the centroid instead of the area, and the cat went with it.

    It's not really causing any problems I'm aware of; it's just odd.

Thanks, Dave

On 11/27/16 13:24, Helmut Kudrnovsky wrote:

Dave Roberts wrote

After editing a map with wxgui I ended up with 39 areas and 38
centroids. How do I find and delete the area with no centroid?

I have tried many combinations of v.info, v.category, v.to.db, and
visualizing with d.vect. If I use v.clean tool=rmarea with slowly
increasing thresholds it gets rid of an area I want before it finds the
one I don't so I don't think it's a sliver.

GRASS GIS 7.3.svn > v.info demo
  . . .
Number of points: 0 Number of centroids: 38
Number of lines: 0 Number of boundaries: 112
Number of areas: 39 Number of islands: 19
  . . .
GRASS GIS 7.3.svn > v.category demo op=report
Layer/table: 1/demo
type count min max
point 0 0 0
line 0 0 0
boundary 0 0 0
centroid 38 1 75
area 0 0 0
face 0 0 0
kernel 0 0 0
all 38 1 75

Thanks, Dave
--
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grass-user mailing list

grass-user@.osgeo

http://lists.osgeo.org/mailman/listinfo/grass-user

d. vect has following option :

cat: Display category numbers of features

try to display the cat info for the polygones to check where the centroid is
missing.

have then a look at v.extract and extract only these polygones you need.

HTH

-----
best regards
Helmut
--
View this message in context: http://osgeo-org.1560.x6.nabble.com/areas-with-no-centroid-tp5297590p5297591.html
Sent from the Grass - Users mailing list archive at Nabble.com.
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4

Thanks for the suggestion, but the area with no centroid doesn't
have a cat.

that's exactly what I've meant.

then do v.extract cats="cats of the polygones with cat" to extract only
these polygones you need.

from the v.extract manual :

cats=range
Category values
Example: 1,3,7-9,13

-----
best regards
Helmut
--
View this message in context: http://osgeo-org.1560.x6.nabble.com/areas-with-no-centroid-tp5297590p5297603.html
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5

Thanks Helmut

v.extract demo cats=1-100 out=new

worked like a charm! Sorry I missed your point the first time.

Dave

On 11/27/16 23:46, Helmut Kudrnovsky wrote:

Thanks for the suggestion, but the area with no centroid doesn't
have a cat.

that's exactly what I've meant.

then do v.extract cats="cats of the polygones with cat" to extract only
these polygones you need.

from the v.extract manual :

cats=range
Category values
Example: 1,3,7-9,13

-----
best regards
Helmut
--
View this message in context: http://osgeo-org.1560.x6.nabble.com/areas-with-no-centroid-tp5297590p5297603.html
Sent from the Grass - Users mailing list archive at Nabble.com.
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