/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2011, Open Source Geospatial Foundation (OSGeo)
* (C) 2004-2005, Open Geospatial Consortium Inc.
*
* All Rights Reserved. http://www.opengis.org/legal/
*/
/**
* {@linkplain org.opengis.metadata.quality.DataQuality Data quality} and
* {@linkplain org.opengis.metadata.quality.PositionalAccuracy positional accuracy}.
* The following is adapted from
* <A HREF="http://portal.opengeospatial.org/files/?artifact_id=6716">OpenGIS®
* Spatial Referencing by Coordinates (Topic 2)</A> specification.
*
* <P ALIGN="justify">The parameters that define a coordinate reference system
* are chosen rather than measured to satisfy the degrees-of-freedom problem in
* the changeover from observation to coordinate quantities. Coordinate reference
* systems are therefore by definition error-free (i.e., non-stochastic).
* A coordinate reference system is realised through a network of control points.
* The coordinates of those control points, derived from surface and/or from
* satellite observations, are stochastic. Their accuracy can be expressed in a
* covariance matrix, which, due to the degrees-of-freedom problem, will have a
* rank deficiency, described in geodetic literature.</P>
*
* <P ALIGN="justify">Coordinate transformations between coordinate reference
* systems usually have parameter values derived from two sets of point coordinates,
* one set in system 1, the other set in system 2. As these coordinates are stochastic
* (i.e., have random-error characteristics) the derived transformation parameter
* values will also be stochastic. Their covariance matrix can be calculated.</P>
*
* <P ALIGN="justify">Coordinates that have not been "naturally" determined in
* coordinate reference system 2, but have been determined in coordinate system 1
* and then transformed to system 2, have the random error effects of the
* transformation superimposed on their original error characteristics. It may be
* possible in well-controlled cases to calculate the covariance matrices of the
* point coordinates before and after the transformation, and thus isolate the
* effect of the transformation, but in practice a user will only be interested
* in the accuracy of the final transformed coordinates.</P>
*
* <P ALIGN="justify">Nevertheless the option is offered to specify the
* covariance matrix of point coordinates resulting exclusively from the
* transformation. It is outside the scope of this specification to describe
* how that covariance matrix should be used. Because a covariance matrix is
* symmetrical, only the upper or lower diagonal part (including the main diagonal)
* needs to be specified.</P>
*
* <P ALIGN="justify">For some transformations, this accuracy information is
* compacted in some assessment of an average impact on horizontal position and
* vertical position, allowing specification of average absolute accuracy and,
* when relevant and available, average relative accuracy. Hence separate quality
* measures may be specified for horizontal and for vertical position in those
* objects.</P>
*
* @version <A HREF="http://www.opengeospatial.org/standards/as#01-111">ISO 19115</A>
* @since GeoAPI 2.0
*/
package org.opengis.metadata.quality;