Limiting precision in vector nodes - Revision history

Neteler: +URL GeographicLib: Support for high precision arithmetic

2018-04-23T22:45:05Z

+URL GeographicLib: Support for high precision arithmetic

← Older revision		Revision as of 22:45, 23 April 2018
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	* [http://www.ibm.com/developerworks/library/j-jtp0114/ Tricks and traps with floating point and decimal numbers] by Brian Goetz		* [http://www.ibm.com/developerworks/library/j-jtp0114/ Tricks and traps with floating point and decimal numbers] by Brian Goetz
	* [http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html What Every Computer Scientist Should Know About Floating-Point Arithmetic] by David Goldberg		* [http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html What Every Computer Scientist Should Know About Floating-Point Arithmetic] by David Goldberg
			* [https://geographiclib.sourceforge.io/html/highprec.html GeographicLib: Support for high precision arithmetic]

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

Neteler: +Category: Vector

2013-07-12T09:23:14Z

+Category: Vector

← Older revision		Revision as of 09:23, 12 July 2013
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	Any connected databases will need to be copied or reconnected. (see the {{Cmd\|v.db.connect}} module)		Any connected databases will need to be copied or reconnected. (see the {{Cmd\|v.db.connect}} module)


	== See also ==		== See also ==
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	[[Category: FAQ]]		[[Category: FAQ]]
			[[Category: Vector]]

⚠️HamishBowman at 04:30, 12 July 2013

2013-07-12T04:30:17Z

← Older revision		Revision as of 04:30, 12 July 2013
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	{{Cmd\|v.out.ascii}} in=quads format=standard dp=3 \| {{Cmd\|v.in.ascii}} out=quads_dp3 format=standard		{{Cmd\|v.out.ascii}} in=quads format=standard dp=3 \| {{Cmd\|v.in.ascii}} out=quads_dp3 format=standard

	Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)		Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology-building messages upon import. (in case of errors make sure that the original map did not have them too)

	Any connected databases will need to be copied or reconnected. (see the {{Cmd\|v.db.connect}} module)		Any connected databases will need to be copied or reconnected. (see the {{Cmd\|v.db.connect}} module)

⚠️HamishBowman at 01:10, 12 July 2013

2013-07-12T01:10:58Z

← Older revision		Revision as of 01:10, 12 July 2013
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	Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce the node coordinates of vector polygons (''areas'') to three decimal digit precision:		Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce the node coordinates of vector polygons (''areas'') to three decimal digit precision:

	{{Cmd\|v.out.ascii}} in=quads format=standard dp=3 \| v.in.ascii out=quads_dp3 format=standard		{{Cmd\|v.out.ascii}} in=quads format=standard dp=3 \| {{Cmd\|v.in.ascii}} out=quads_dp3 format=standard

	Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)		Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)

⚠️HamishBowman at 01:10, 12 July 2013

2013-07-12T01:10:30Z

← Older revision		Revision as of 01:10, 12 July 2013
Line 3:		Line 3:
	Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce the node coordinates of vector polygons (''areas'') to three decimal digit precision:		Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce the node coordinates of vector polygons (''areas'') to three decimal digit precision:

	v.out.ascii in=quads format=standard dp=3 \| v.in.ascii out=quads_dp3 format=standard		{{Cmd\|v.out.ascii}} in=quads format=standard dp=3 \| v.in.ascii out=quads_dp3 format=standard

	Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)		Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)

⚠️HamishBowman: v.db.connect

2013-07-12T01:09:54Z

v.db.connect

← Older revision		Revision as of 01:09, 12 July 2013
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	Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)		Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)

			Any connected databases will need to be copied or reconnected. (see the {{Cmd\|v.db.connect}} module)

⚠️HamishBowman: minor wording

2013-07-12T01:07:04Z

minor wording

← Older revision		Revision as of 01:07, 12 July 2013
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	There are specifications (e.g. the Greek Cadastral System) which ask the digitizer to create their data with (for example) three digits behind the decimal place. As a general rule for the overwhelming majority of modern computers, exact representation of IEEE floating point numbers is not guaranteed in binary data storage (see links below), but if it's what the spec says it's what has to be attempted anyway.		There are specifications (e.g. the Greek Cadastral System) which ask the digitizer to create their data with (for example) three digits behind the decimal place. As a general rule for the overwhelming majority of modern computers, exact representation of IEEE floating point numbers is not guaranteed in binary data storage (see links below), but if it's what the spec says it's what has to be attempted anyway.

	Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce vector ~~area~~ polygons ~~node coordinates~~ to three decimal digit precision:		Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce the node coordinates of vector polygons (''areas'') to three decimal digit precision:

	v.out.ascii in=quads format=standard dp=3 \| v.in.ascii out=quads_dp3 format=standard		v.out.ascii in=quads format=standard dp=3 \| v.in.ascii out=quads_dp3 format=standard

⚠️HamishBowman: howto

2013-07-12T00:59:32Z

howto

New page

There are specifications (e.g. the Greek Cadastral System) which ask the digitizer to create their data with (for example) three digits behind the decimal place. As a general rule for the overwhelming majority of modern computers, exact representation of IEEE floating point numbers is not guaranteed in binary data storage (see links below), but if it's what the spec says it's what has to be attempted anyway.

Here is an example using the Spearfish sample dataset in GRASS 6.4 to reduce vector area polygons node coordinates to three decimal digit precision:

v.out.ascii in=quads format=standard dp=3 | v.in.ascii out=quads_dp3 format=standard

Topology ''should'' be preserved, but it is worth paying close attention to the verification and topology building messages upon import. (in case of errors make sure that the original map did not have them too)

== See also ==

* [http://www.ibm.com/developerworks/library/j-jtp0114/ Tricks and traps with floating point and decimal numbers] by Brian Goetz
* [http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html What Every Computer Scientist Should Know About Floating-Point Arithmetic] by David Goldberg

[[Category: FAQ]]