Integrity - Revision history

Claudia.Prajanu at 13:06, 26 July 2018

2018-07-26T13:06:00Z

← Older revision		Revision as of 13:06, 26 July 2018
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	* A hazardously misleading information event occurs when, being the system declared available, the position error exceeds the alert limit.		* A hazardously misleading information event occurs when, being the system declared available, the position error exceeds the alert limit.

	The ''Stanford diagram'' (or ''Stanford plot'') introduced in <ref>~~[http://waas.stanford.edu/metrics.html~~ WAAS Precision Approach Metrics: Accuracy, Integrity, Continuity and Availability - Oct 1999]</ref> and improved in <ref>[[The Stanford – ESA Integrity Diagram: Focusing on SBAS Integrity]]</ref> is a quite handy tool to explain an illustrate most of these concepts and their relations (as well as to asses positioning systems’ performance). The layout of a generic Stanford diagram is shown below, in the Stanford diagram figure. For each sample position and protection level, a point is plotted in the Stanford diagram whose abscissa represents the absolute position error and whose ordinate represents its associated protection level. Usually, separate Stanford plots are represented for the horizontal and vertical components of position errors (and corresponding horizontal and vertical protection levels, respectively). The diagonal axis separates those samples in which the position error is covered by the protection level, above the diagonal, from those, below the diagonal, in which the protection level fails to cover the position error. Stanford plots allow an easy and quick check that integrity holds, just by making sure that all sample points lie on the upper side of the diagonal axis. Also, the proximity of the cloud of sample points to the diagonal gives an idea of the achieved level of safety, as any point above the diagonal but very close to it indicates that an ''integrity event'' was close to occur.		The ''Stanford diagram'' (or ''Stanford plot'') introduced in <ref> WAAS Precision Approach Metrics: Accuracy, Integrity, Continuity and Availability - Oct 1999</ref> and improved in <ref>[[The Stanford – ESA Integrity Diagram: Focusing on SBAS Integrity]]</ref> is a quite handy tool to explain an illustrate most of these concepts and their relations (as well as to asses positioning systems’ performance). The layout of a generic Stanford diagram is shown below, in the Stanford diagram figure. For each sample position and protection level, a point is plotted in the Stanford diagram whose abscissa represents the absolute position error and whose ordinate represents its associated protection level. Usually, separate Stanford plots are represented for the horizontal and vertical components of position errors (and corresponding horizontal and vertical protection levels, respectively). The diagonal axis separates those samples in which the position error is covered by the protection level, above the diagonal, from those, below the diagonal, in which the protection level fails to cover the position error. Stanford plots allow an easy and quick check that integrity holds, just by making sure that all sample points lie on the upper side of the diagonal axis. Also, the proximity of the cloud of sample points to the diagonal gives an idea of the achieved level of safety, as any point above the diagonal but very close to it indicates that an ''integrity event'' was close to occur.

	Both MI and HMI events can either be horizontal or vertical. In the Stanford diagram, as depicted in the figure above, MI events would be represented by those sample points lying below the diagonal axis and on the left-hand side of the vertical dashed line (which is placed at the abscissa equal to the alert limit). The HMI events would be represented by points lying on the right-hand side of the vertical dashed line and below the horizontal dashed line (which is placed at the ordinate equal to the alert limit).		Both MI and HMI events can either be horizontal or vertical. In the Stanford diagram, as depicted in the figure above, MI events would be represented by those sample points lying below the diagonal axis and on the left-hand side of the vertical dashed line (which is placed at the abscissa equal to the alert limit). The HMI events would be represented by points lying on the right-hand side of the vertical dashed line and below the horizontal dashed line (which is placed at the ordinate equal to the alert limit).

Filipe.Pelica: Included editor logo.

2014-09-18T16:49:10Z

Included editor logo.

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	\|Level=Basic		\|Level=Basic
	\|YearOfPublication=2011		\|YearOfPublication=2011
			\|Logo=GMV
	\|Title={{PAGENAME}}		\|Title={{PAGENAME}}
	}}		}}

Teresa.Ferreira: /* Integrity vs. Accuracy */

2013-12-16T18:46:34Z

Integrity vs. Accuracy

← Older revision		Revision as of 18:46, 16 December 2013
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	* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.		* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.
	* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.		* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.
	* From a system performance perspective, accuracy is understood as a global system characteristic, whereas integrity is rather intended as real time decision criterion for using or not using the system. For this reason, it has been a common practice to associate integrity with a mechanism, or set of mechanisms (barriers) that is part of the integrity assurance chain but at the same time is completely independent of the other parts of the system for which integrity is to be assured. Examples of this (although not at user level) are [[EGNOS General Introduction\|EGNOS]] CPF Check Set (independent from CPF Processing Set) or [[GALILEO General Introduction\|Galileo]] GCC IPF (independent from GCC OSPF).		* From a system performance perspective, accuracy is understood as a global system characteristic, whereas integrity is rather intended as real time decision criterion for using or not using the system. For this reason, it has been a common practice to associate integrity with a mechanism, or set of mechanisms (barriers) that is part of the integrity assurance chain but at the same time is completely independent of the other parts of the system for which integrity is to be assured.

	==Integrity Parameters==		==Integrity Parameters==

Teresa.Ferreira at 18:45, 16 December 2013

2013-12-16T18:45:24Z

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	Finally, Stanford diagrams allow also to asses compliance of system availability requirements, which in the plot appear as points whose ordinate is above the alert limit. Hence, correct system performance (in terms of availability and integrity) when all points in the Stanford plot lie inside the triangle defined by the ordinate axis, the diagonal axis, and the horizontal dashed line. [[Accuracy]] could also be assessed by including a vertical line in the diagram at the abscissa equal to the target error upper bound, those points lying on the left-hand side of that line corresponding to correct system accuracy performance.		Finally, Stanford diagrams allow also to asses compliance of system availability requirements, which in the plot appear as points whose ordinate is above the alert limit. Hence, correct system performance (in terms of availability and integrity) when all points in the Stanford plot lie inside the triangle defined by the ordinate axis, the diagonal axis, and the horizontal dashed line. [[Accuracy]] could also be assessed by including a vertical line in the diagram at the abscissa equal to the target error upper bound, those points lying on the left-hand side of that line corresponding to correct system accuracy performance.


	~~==Integrity in Galileo==~~

	All the concepts defined so far had their origin in the civil aviation world, and some of them achieved their current degree of maturity thanks to the advent of SBAS systems (and, in particular, of the American WAAS system). The new integrity concept defined for Galileo, conceived for safety-of-life applications, has not yet been adopted by the civil aviation, but also offers a way to achieve GNSS integrity which must be taken into account not only in the context of safety-of-life applications, but also in that of liability critical applications. However, the Galileo integrity concept can be considered to be equivalent to the integrity concepts adopted so far by the civil aviation, the main difference being that, instead of fixing the integrity risk and then computing an associated protection level, Galileo users should fix a target protection level (or similar concept) and then compute the associated integrity risk by means of the integrity information broadcast by Galileo satellites.

	~~Additional information about the Galileo Integrity Concept can be found [[Galileo integrity concept\|here]].~~

	==Notes==		==Notes==

Carlos.Lopez at 11:33, 23 February 2012

2012-02-23T11:33:46Z

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	{{Article Infobox2		{{Article Infobox2
	\|Category=Fundamentals		\|Category=Fundamentals
	\|~~Title={{PAGENAME}}~~		\|Editors=GMV
	~~\|Authors~~=GMV
	\|Level=Basic		\|Level=Basic
	\|YearOfPublication=2011		\|YearOfPublication=2011
	\|~~Logo~~=~~GMV~~		\|Title={{PAGENAME}}
	}}		}}

	Integrity is the measure of the trust that can be placed in the correctness of the information supplied by a navigation system. Integrity includes the ability of the system to provide timely warnings to users when the system should not be used for navigation{{#tag:ref\| This definition was adapted from the [http://www.navcen.uscg.gov/pdf/2008_Federal_Radionavigation_Plan.pdf 2008 US Federal Radionavigation Plan]<ref> [http://www.navcen.uscg.gov/pdf/2008_Federal_Radionavigation_Plan.pdf US Federal Radionavigation Plan], DOT-VNTSC-RITA-08-02/DoD-4650.5, 2008</ref>\|group="nb"}}.		Integrity is the measure of the trust that can be placed in the correctness of the information supplied by a navigation system. Integrity includes the ability of the system to provide timely warnings to users when the system should not be used for navigation{{#tag:ref\| This definition was adapted from the [http://www.navcen.uscg.gov/pdf/2008_Federal_Radionavigation_Plan.pdf 2008 US Federal Radionavigation Plan]<ref> [http://www.navcen.uscg.gov/pdf/2008_Federal_Radionavigation_Plan.pdf US Federal Radionavigation Plan], DOT-VNTSC-RITA-08-02/DoD-4650.5, 2008</ref>\|group="nb"}}.

Rui.Pereira at 14:40, 29 June 2011

2011-06-29T14:40:58Z

← Older revision		Revision as of 14:40, 29 June 2011
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	* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.		* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.
	* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.		* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.
	* From a system performance perspective, accuracy is understood as a global system characteristic, whereas integrity is rather intended as real time decision criterion for using or not using the system. For this reason, it has been a common practice to associate integrity with a mechanism, or set of mechanisms (barriers) that is part of the integrity assurance chain but at the same time is completely independent of the other parts of the system for which integrity is to be assured. Examples of this (although not at user level) are [[EGNOS]] CPF Check Set (independent from CPF Processing Set) or [[Galileo]] GCC IPF (independent from GCC OSPF).		* From a system performance perspective, accuracy is understood as a global system characteristic, whereas integrity is rather intended as real time decision criterion for using or not using the system. For this reason, it has been a common practice to associate integrity with a mechanism, or set of mechanisms (barriers) that is part of the integrity assurance chain but at the same time is completely independent of the other parts of the system for which integrity is to be assured. Examples of this (although not at user level) are [[EGNOS General Introduction\|EGNOS]] CPF Check Set (independent from CPF Processing Set) or [[GALILEO General Introduction\|Galileo]] GCC IPF (independent from GCC OSPF).

	==Integrity Parameters==		==Integrity Parameters==

Rui.Pereira at 16:57, 29 April 2011

2011-04-29T16:57:50Z

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	==Alert Limit==		===Alert Limit===

	The alert limit for a given parameter measurement is the error tolerance not to be exceeded without issuing an alert.		The alert limit for a given parameter measurement is the error tolerance not to be exceeded without issuing an alert.
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	==Time to Alert==		===Time to Alert===

	When an integrity event occurs, an alarm should be raised within a prescribed (rather short) time lapse after the event (this is the “ability to provide timely warnings” mentioned in the formal definition of integrity). Said prescribed time lapse is known as the ''time to alert'' (TTA), defined in <ref name="Annex10"/> as:		When an integrity event occurs, an alarm should be raised within a prescribed (rather short) time lapse after the event (this is the “ability to provide timely warnings” mentioned in the formal definition of integrity). Said prescribed time lapse is known as the ''time to alert'' (TTA), defined in <ref name="Annex10"/> as:
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	==Integrity Risk==		===Integrity Risk===

	The integrity risk, although not explicitly defined in the civil aviation standards, is a bound to the probability that integrity is not achieved, which must be prescribed for each system or system's application or operating mode as a requirement. Hence:		The integrity risk, although not explicitly defined in the civil aviation standards, is a bound to the probability that integrity is not achieved, which must be prescribed for each system or system's application or operating mode as a requirement. Hence:
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	==Protection Level==		===Protection Level===

	Since during normal operations it is not possible to know the position error of an aircraft, a statistical bound to position error called protection level needs to be computed in order to be able to measure the risk that the alert limit is surpassed. Hence, the system is not declared unavailable when the alert limit is exceeded by the actual position error, but by the protection level (as then the risk for position error to exceed the alert limit would be above the target integrity risk). Protection level is defined by ICAO<ref name="Annex10"/> as follows:		Since during normal operations it is not possible to know the position error of an aircraft, a statistical bound to position error called protection level needs to be computed in order to be able to measure the risk that the alert limit is surpassed. Hence, the system is not declared unavailable when the alert limit is exceeded by the actual position error, but by the protection level (as then the risk for position error to exceed the alert limit would be above the target integrity risk). Protection level is defined by ICAO<ref name="Annex10"/> as follows:
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	Note that any reference to false alarm probability has been intentionally omitted. False alarm probability requirements (if applicable) for any particular positioning system could then be specified, thus setting restrictions to how loose a bound the protection level can be, but this is kept independent of the protection level concept itself. The concepts of horizontal protection level (HPL) and vertical protection level (VPL) are graphically represented in the Horizontal and vertical protection levels figure.		Note that any reference to false alarm probability has been intentionally omitted. False alarm probability requirements (if applicable) for any particular positioning system could then be specified, thus setting restrictions to how loose a bound the protection level can be, but this is kept independent of the protection level concept itself. The concepts of horizontal protection level (HPL) and vertical protection level (VPL) are graphically represented in the Horizontal and vertical protection levels figure.

	Related with the protection ~~lever~~ are ''integrity ~~event~~'' that are defined as:		Related with the protection level are ''integrity events'' that are defined as:

	:A horizontal (respectively vertical) integrity event occurs whenever the horizontal (respectively vertical) position error exceeds the horizontal (respectively vertical) protection level.		:A horizontal (respectively vertical) integrity event occurs whenever the horizontal (respectively vertical) position error exceeds the horizontal (respectively vertical) protection level.

Rui.Pereira at 16:55, 29 April 2011

2011-04-29T16:55:14Z

Show changes

Duarte.Sampaio: /* Integrity vs. Accuracy */

2011-04-13T14:57:49Z

Integrity vs. Accuracy

← Older revision		Revision as of 14:57, 13 April 2011
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	As it has often been cause of confusion, it is worth trying to clarify the distinction between accuracy and integrity:		As it has often been cause of confusion, it is worth trying to clarify the distinction between accuracy and integrity:
	[[File:Accuracy_VS_Integrity.png\|~~left~~\|thumb\|500px\|alt=Accuracy and Integrity\|Accuracy and Integrity]]
			[[File:Accuracy_VS_Integrity.png\|right\|thumb\|500px\|alt=Accuracy and Integrity\|Accuracy and Integrity]]

	* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.		* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.
	* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.		* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.

Duarte.Sampaio: /* Integrity vs. Accuracy */

2011-04-13T14:41:09Z

Integrity vs. Accuracy

← Older revision		Revision as of 14:41, 13 April 2011
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	As it has often been cause of confusion, it is worth trying to clarify the distinction between accuracy and integrity:		As it has often been cause of confusion, it is worth trying to clarify the distinction between accuracy and integrity:
			[[File:Accuracy_VS_Integrity.png\|left\|thumb\|500px\|alt=Accuracy and Integrity\|Accuracy and Integrity]]
	* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.		* From a mathematical point of view, the main difference between them is the point of the tail of the statistical distribution of errors at which to place the cut-off. For instance, civil aviation requirements tend to measure accuracy at the 95% percentile (e.g. "95% of the errors shall be below such and such..."), whereas integrity requirements refer to percentiles that range between 99.999% and 99.9999999% (depending on the particular topic under consideration). The intention behind this is to keep the probability of hazardous situations (that would possibly put at risk human lives) extremely low.
	* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.		* Another key difference is in the alarms; integrity requirements involve alarms being raised when system's performance is bad enough to become risky, while accuracy requirements do not.