Vector topology - Revision history

Neteler: added link to progman

2023-10-10T07:36:23Z

added link to progman

← Older revision		Revision as of 07:36, 10 October 2023
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	* Intro to [[Vector Database Management\|vector data model]] (with drawing)		* Intro to [[Vector Database Management\|vector data model]] (with drawing)
	* More user-oriented topology details in the manual at: [~~http~~://grass.osgeo.org/grass-stable/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]		* More user-oriented topology details in the manual at: [https://grass.osgeo.org/grass-stable/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]
			* [https://grass.osgeo.org/programming8/vectorlib.html Vectorlib in the GRASS GIS 8 Programmer's Manual]

	== GRASS GIS: pseudo-topology and real topology ==		== GRASS GIS: pseudo-topology and real topology ==

Neteler: /* Topology general characteristics */

2023-10-10T07:25:24Z

Topology general characteristics

← Older revision		Revision as of 07:25, 10 October 2023
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	Vector map topology can be cleaned at user level by {{cmd\|v.clean}} command.		Vector map topology can be cleaned at user level by {{cmd\|v.clean}} command.

	More details in the manual at: [http://grass.osgeo.org/grass-stable/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]		* Intro to [[Vector Database Management\|vector data model]] (with drawing)
			* More user-oriented topology details in the manual at: [http://grass.osgeo.org/grass-stable/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]

	== GRASS GIS: pseudo-topology and real topology ==		== GRASS GIS: pseudo-topology and real topology ==

Neteler: /* See also */ programming7 -> programming8

2023-10-10T07:24:32Z

Neteler: update grass70 -> stable

2023-10-10T07:23:49Z

update grass70 -> stable

← Older revision		Revision as of 07:23, 10 October 2023
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	Vector map topology can be cleaned at user level by {{cmd\|v.clean}} command.		Vector map topology can be cleaned at user level by {{cmd\|v.clean}} command.

	More details in the manual at: [http://grass.osgeo.org/~~grass70~~/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]		More details in the manual at: [http://grass.osgeo.org/grass-stable/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]

	== GRASS GIS: pseudo-topology and real topology ==		== GRASS GIS: pseudo-topology and real topology ==

Neteler: +Extracts nodes by number of line connections

2022-08-27T14:27:39Z

+Extracts nodes by number of line connections

← Older revision		Revision as of 14:27, 27 August 2022
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	If you want only isles and not regular areas in the SHAPE file, use <tt>{{cmd\|v.centroids}} layer=X</tt> with a layer number that is unused, then <tt>{{cmd\|v.out.ogr}} layer=X</tt> to write out the islands.		If you want only isles and not regular areas in the SHAPE file, use <tt>{{cmd\|v.centroids}} layer=X</tt> with a layer number that is unused, then <tt>{{cmd\|v.out.ogr}} layer=X</tt> to write out the islands.

			== Extracts nodes by number of line connections ==

			See: https://gist.github.com/petrasovaa/356b2bf9671b2b6801963f4368d7db0b

	== See also ==		== See also ==

Neteler: +Vector data export

2015-06-09T20:29:07Z

+Vector data export

← Older revision		Revision as of 20:29, 9 June 2015
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	== GRASS GIS topology management ==		== GRASS GIS topology management ==

	Topology general characteristics:		=== Topology general characteristics ===

	* geometry and attributes are stored separately (concept: ''don't read both if it is not necessary'' - usually it is not)		* geometry and attributes are stored separately (concept: ''don't read both if it is not necessary'' - usually it is not)
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	* currently only 2D topology is supported (also 3D faces but no true 3D topology with kernels)		* currently only 2D topology is supported (also 3D faces but no true 3D topology with kernels)

	Topology is ~~written~~ for '''native GRASS GIS vector format'''~~; in~~ case of linked OGR sources (see {{cmd\|v.external}} module), only pseudo-topology (boundaries constructed from polygons) is written.		Topology is stored for '''native GRASS GIS vector format''' (the default). In case of linked OGR sources (see {{cmd\|v.external}} module), only pseudo-topology (boundaries constructed from polygons) is written.

	The following rules apply to the vector data:		The following '''topological rules''' apply to the vector data:

	* Boundaries should not cross each other (i.e., boundaries which would cross must be split at their intersection to form distict boundaries). On the contrary, lines can cross each other, e.g. bridges over rivers.		* Boundaries should not cross each other (i.e., boundaries which would cross must be split at their intersection to form distict boundaries). On the contrary, lines can cross each other, e.g. bridges over rivers.
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	</pre>		</pre>

	=== See also ===		== Vector data export ==

			The topological GRASS GIS vector data can be written out to common GIS vector formats with <tt>{{cmd\|v.out.ogr}}</tt>.

			=== Export of islands ===

			If you want only isles and not regular areas in the SHAPE file, use <tt>{{cmd\|v.centroids}} layer=X</tt> with a layer number that is unused, then <tt>{{cmd\|v.out.ogr}} layer=X</tt> to write out the islands.

			== See also ==

	* [[Vector topology cleaning]]		* [[Vector topology cleaning]]

Neteler: +Intro added from http://grass.osgeo.org/programming7/vlibTopology.html

2015-06-08T21:17:51Z

+Intro added from http://grass.osgeo.org/programming7/vlibTopology.html

← Older revision		Revision as of 21:17, 8 June 2015
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	'''Q:''' What is the difference between pseudo-topology and real topology?
			== GRASS GIS topology management ==

			Topology general characteristics:

			* geometry and attributes are stored separately (concept: ''don't read both if it is not necessary'' - usually it is not)
			* the format is topological (areas build from boundaries)
			* currently only 2D topology is supported (also 3D faces but no true 3D topology with kernels)

			Topology is written for '''native GRASS GIS vector format'''; in case of linked OGR sources (see {{cmd\|v.external}} module), only pseudo-topology (boundaries constructed from polygons) is written.

			The following rules apply to the vector data:

			* Boundaries should not cross each other (i.e., boundaries which would cross must be split at their intersection to form distict boundaries). On the contrary, lines can cross each other, e.g. bridges over rivers.
			* Lines and boundaries share nodes only if their endpoints are identical. Lines or boundaries can be forced to share a common node by snapping them together. This is particulary important since nodes are not represented in the coor file, but only implicitly as endpoints of lines and boundaries.
			* Common area boundaries should appear only once (i.e., should not be double digitized).
			* Areas must be explicitly closed. This means that it must be possible to complete each area by following one or more boundaries that are connected by common nodes, and that such tracings result in closed areas.
			* It is recommended that area features and linear features be placed in separate layers. However if area features and linear features must appear in one layer, common boundaries should be digitized only once. For example, a boundary that is also a line (e.g., a road which is also a field boundary), should be digitized as a boundary to complete the area(s), and a boundary which is functionally also a line should be labeled as a line by a distinct category number.

			Vector map topology can be cleaned at user level by {{cmd\|v.clean}} command.

			More details in the manual at: [http://grass.osgeo.org/grass70/manuals/vectorintro.html#vector-model-and-topology Vector model and topology]

			== GRASS GIS: pseudo-topology and real topology ==

			'''Q:''' What is the difference between pseudo-topology (v.external`) and real topology?

	'''A:''' The differences are listed in the table below.		'''A:''' The differences are listed in the table below.

Neteler: /* See also */

2014-12-04T07:22:01Z

Neteler: /* See also */

2014-11-20T20:14:54Z

Neteler: link to progman7

2014-03-05T09:43:33Z

link to progman7

← Older revision		Revision as of 09:43, 5 March 2014
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	* [[Vector topology cleaning]]		* [[Vector topology cleaning]]
			* see also [http://grass.osgeo.org/programming7/vectorlib.html#vlibTopoManagement Vector library topology management] background

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Topology]]		[[Category:Topology]]
	[[Category:Vector]]		[[Category:Vector]]

← Older revision		Revision as of 07:24, 10 October 2023
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	* [[Vector topology cleaning]]		* [[Vector topology cleaning]]
	* Intro to [[Vector Database Management\|vector data model]] (with drawing)		* Intro to [[Vector Database Management\|vector data model]] (with drawing)
	* see also [http://grass.osgeo.org/~~programming7~~/vectorlib.html#vlibTopoManagement Vector library topology management] background		* see also [http://grass.osgeo.org/programming8/vectorlib.html#vlibTopoManagement Vector library topology management] background
	* [[Vector patching]]		* [[Vector patching]]

← Older revision		Revision as of 07:22, 4 December 2014
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	* [[Vector topology cleaning]]		* [[Vector topology cleaning]]
			* Intro to [[Vector Database Management\|vector data model]] (with drawing)
	* see also [http://grass.osgeo.org/programming7/vectorlib.html#vlibTopoManagement Vector library topology management] background		* see also [http://grass.osgeo.org/programming7/vectorlib.html#vlibTopoManagement Vector library topology management] background
	* [[Vector patching]]		* [[Vector patching]]

← Older revision		Revision as of 20:14, 20 November 2014
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	* [[Vector topology cleaning]]		* [[Vector topology cleaning]]
	* see also [http://grass.osgeo.org/programming7/vectorlib.html#vlibTopoManagement Vector library topology management] background		* see also [http://grass.osgeo.org/programming7/vectorlib.html#vlibTopoManagement Vector library topology management] background
			* [[Vector patching]]

	[[Category:FAQ]]		[[Category:FAQ]]
	[[Category:Topology]]		[[Category:Topology]]
	[[Category:Vector]]		[[Category:Vector]]