Opened 5 years ago

Last modified 5 years ago

#2550 new defect

Polygons disappear after v.generalize simplification

Reported by: dido Owned by: grass-dev@…
Priority: major Milestone: 6.4.6
Component: Vector Version: 6.4.4
Keywords: Polygons disappear v.generalize simplification Cc:
CPU: x86-64 Platform: MSWindows 7

Description

Polygons disappear after v.generalize simplification.

A large rectangular polygon dataset is used with ~14 000 features. Polygons are first processed with rmarea to remove all polygons of size 900 m2. Then a simplification is executed with v.generalize using a factor of 10, all other parameters defaulted.

After simplification several large polygons are missing from the set rendering it useless.

System is a win7x64; QGIS 2.6.1 and GRASS 6.4.4

Dataset can be provided upon request (being a 7.5mb shapefile).

Change History (5)

comment:1 in reply to:  description Changed 5 years ago by mmetz

Replying to dido:

Polygons disappear after v.generalize simplification.

A large rectangular polygon dataset is used with ~14 000 features. Polygons are first processed with rmarea to remove all polygons of size 900 m2. Then a simplification is executed with v.generalize using a factor of 10, all other parameters defaulted.

After simplification several large polygons are missing from the set rendering it useless.

System is a win7x64; QGIS 2.6.1 and GRASS 6.4.4

Dataset can be provided upon request (being a 7.5mb shapefile).

I assume the workflow is v.in.ogr + v.clean tool=rmarea + v.generalize threshold=10.

Several functions relating to v.generalize have just been fixed in trunk and I would like to test. Can you please provide a link to the shapefile or send the shapefile to markus.metz.giswork at gmail dot com? Thanks!

comment:2 Changed 5 years ago by dido

Import is done using v.in.ogr with snapping threshold = 1 and min area = 0.000000000001. This one probably engages a v.clean operation also.

I've sent you a temporary download link for the dataset.

comment:3 in reply to:  description Changed 5 years ago by mmetz

Replying to dido:

Polygons disappear after v.generalize simplification.

A large rectangular polygon dataset is used with ~14 000 features. Polygons are first processed with rmarea to remove all polygons of size 900 m2. Then a simplification is executed with v.generalize using a factor of 10, all other parameters defaulted.

After simplification several large polygons are missing from the set rendering it useless.

I can confirm the problem. This is a bug in the vector libraries regarding topology updating and has been fixed in GRASS 7. Please wait for GRASS 7.0.0RC2 or use a daily build.

comment:4 Changed 5 years ago by martinl

Milestone: 6.4.5

Ticket retargeted after milestone closed

comment:5 Changed 5 years ago by martinl

Milestone: 6.4.6
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