Create concave hull - Revision history

Neteler: finetuning

2015-06-03T13:45:10Z

finetuning

← Older revision		Revision as of 13:45, 3 June 2015
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	A: You can approximate a concave hull through the following steps:		A: You can approximate a concave hull through the following steps:

	=== GRASS 6 ===		=== GRASS GIS 6 ===
	* create map of lines connecting all points (I find it easier to do this with {{cmd\|v.net.visibility}}, but {{cmd\|v.distance}} works also)		* create map of lines connecting all points (I find it easier to do this with {{cmd\|v.net.visibility}}, but {{cmd\|v.distance}} works also)
	* add a table with a column 'cat' and a column 'length double precision' and categories to these lines ({{cmd\|v.db.addtable}}, {{cmd\|v.category}})		* add a table with a column 'cat' and a column 'length double precision' and categories to these lines ({{cmd\|v.db.addtable}}, {{cmd\|v.category}})
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	* dissolve the areas into one ({{cmd\|v.dissolve}})		* dissolve the areas into one ({{cmd\|v.dissolve}})

	=== GRASS 7 ===		=== GRASS GIS 7 ===

	The addon {{AddonSrc\|vector\|v.concave.hull\|version=7}} creates a concave hull using Delaunay triangulation.		The addon {{AddonCmd\|v.concave.hull}} ({{AddonSrc\|vector\|v.concave.hull\|version=7}}) creates a concave hull using Delaunay triangulation.

	The image shows the results:		The image shows the results:

Neteler: cosmetics

2013-02-25T17:11:44Z

cosmetics

← Older revision		Revision as of 17:11, 25 February 2013
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	Q: I have a set of points and would like to compute the concave hull of it.		Q: I have a set of points and would like to compute the '''concave hull''' of it (this is not the convex hull as done by {{cmd\|v.hull}}):

	A: You can approximate a concave hull through the following steps:		A: You can approximate a concave hull through the following steps:

	* create map of lines connecting all points (I find it easier to do this with v.net.visibility, but v.distance works also)		=== GRASS 6 ===
	* add a table with a column 'cat' and a column 'length double precision' and categories to these lines (v.db.addtable, v.category)		* create map of lines connecting all points (I find it easier to do this with {{cmd\|v.net.visibility}}, but {{cmd\|v.distance}} works also)
	* upload the length of each line to the table (v.to.db)		* add a table with a column 'cat' and a column 'length double precision' and categories to these lines ({{cmd\|v.db.addtable}}, {{cmd\|v.category}})
			* upload the length of each line to the table ({{cmd\|v.to.db}})
	* visually identify a length threshold above which the lines should not be used		* visually identify a length threshold above which the lines should not be used
	* extract only those lines below that threshold (v.extract where="length<MAXLENGTH)		* extract only those lines below that threshold ({{cmd\|v.extract}} where="length<MAXLENGTH)
	* convert the lines to boundaries (v.type)		* convert the lines to boundaries ({{cmd\|v.type}})
	* break overlapping lines (v.clean tool=break, there shouldn't be any duplicate lines, but just in case you can also use rmdupl)		* break overlapping lines ({{cmd\|v.clean}} tool=break, there shouldn't be any duplicate lines, but just in case you can also use rmdupl)
	* add centroids with the same category value to the boundaries (v.centroids step=0)		* add centroids with the same category value to the boundaries ({{cmd\|v.centroids}} step=0)
	* dissolve the areas into one (v.dissolve)		* dissolve the areas into one ({{cmd\|v.dissolve}})

	~~Alternatively, the~~ addon {{AddonSrc\|vector\|v.concave.hull\|version=7}} creates a concave hull using ~~delaunay~~ triangulation.		=== GRASS 7 ===

			The addon {{AddonSrc\|vector\|v.concave.hull\|version=7}} creates a concave hull using Delaunay triangulation.

	The image shows the results:		The image shows the results:

⚠️Mmetz: add v.concave.hull

2013-02-22T10:38:46Z

add v.concave.hull

← Older revision		Revision as of 10:38, 22 February 2013
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	* dissolve the areas into one (v.dissolve)		* dissolve the areas into one (v.dissolve)

	The image to shows the results:		Alternatively, the addon {{AddonSrc\|vector\|v.concave.hull\|version=7}} creates a concave hull using delaunay triangulation.

			The image shows the results:

	[[Image:Concave_hull.jpg\|500px]]		[[Image:Concave_hull.jpg\|500px]]

⚠️MilenaN: Reverted edits by Reverse22 (talk) to last revision by Neteler

2011-12-30T21:37:37Z

Reverted edits by Reverse22 (talk) to last revision by Neteler

← Older revision		Revision as of 21:37, 30 December 2011
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	[[Category:FAQ]]		[[Category:FAQ]]


	~~==Other==~~
	~~[http://thetvtopc.com/Reverse_Cell_Phone_Lookup_Number reverse phone lookup]~~

⚠️Reverse22 at 20:49, 30 December 2011

2011-12-30T20:49:13Z

← Older revision		Revision as of 20:49, 30 December 2011
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	[[Category:FAQ]]		[[Category:FAQ]]


			==Other==
			[http://thetvtopc.com/Reverse_Cell_Phone_Lookup_Number reverse phone lookup]

Neteler: Reverted edits by PhillipPlascencia (talk) to last revision by Mlennert

2010-11-27T14:34:21Z

Reverted edits by PhillipPlascencia (talk) to last revision by Mlennert

← Older revision		Revision as of 14:34, 27 November 2010
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	[[Category:FAQ]]		[[Category:FAQ]]

	~~[http://www.thesiswritingservice.com/ thesis writing]~~

⚠️PhillipPlascencia at 14:41, 25 November 2010

2010-11-25T14:41:03Z

← Older revision		Revision as of 14:41, 25 November 2010
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	[[Category:FAQ]]		[[Category:FAQ]]

			[http://www.thesiswritingservice.com/ thesis writing]

⚠️Mlennert: New page: Q: I have a set of points and would like to compute the concave hull of it. A: You can approximate a concave hull through the following steps: * create map of lines connecting all points...

2008-08-10T13:54:58Z

New page: Q: I have a set of points and would like to compute the concave hull of it. A: You can approximate a concave hull through the following steps: * create map of lines connecting all points...

New page

Q: I have a set of points and would like to compute the concave hull of it.

A: You can approximate a concave hull through the following steps:

* create map of lines connecting all points (I find it easier to do this with v.net.visibility, but v.distance works also)
* add a table with a column 'cat' and a column 'length double precision' and categories to these lines (v.db.addtable, v.category)
* upload the length of each line to the table (v.to.db)
* visually identify a length threshold above which the lines should not be used
* extract only those lines below that threshold (v.extract where="length<MAXLENGTH)
* convert the lines to boundaries (v.type)
* break overlapping lines (v.clean tool=break, there shouldn't be any duplicate lines, but just in case you can also use rmdupl)
* add centroids with the same category value to the boundaries (v.centroids step=0)
* dissolve the areas into one (v.dissolve)

The image to shows the results:

[[Image:Concave_hull.jpg|500px]]

[[Category:FAQ]]