Control CoverageFunction CV_ValueObject

Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 25

5.11 CV_InterpolationMethod

CV_InterpolationMethod is a list of codes that identify interpolation methods that may be used for evaluating continuous coverages. See Annex C for descriptions of specific interpolation methods.

5.12 Subclasses of CV_ContinuousCoverage

This International Standard specifies schemas for five subclasses of CV_ContinuousCoverage Figure 4. CV_ThiessenPolygonCoverage is specified in Clause 7, CV_ContinuousQuadrilateralGridCoverage is specified in Clause 8, CV_HexagonalGridCoverage is specified in Clause 9, CV_TINCoverage is specified in Clause 10, and CV_SegmentedCurveCoverage is specified in Clause 11. Figure 4 — Continuous coverages 6 Discrete coverages

6.1 Discrete coverage types

The domain of a CV_DiscreteCoverage consists of a collection of geometric objects. CV_DiscreteCoverages are subclassed on the basis of the type of geometric object in the spatial domain Figure 5. Each subclass of CV_DiscreteCoverage is associated with a specific subclass of CV_GeometryValuePair. The subclasses of both classes inherit the attributes and operations specified for the parent classes, and the association between the parent classes, but with the restrictions described below. Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 26 Figure 5 — Discrete coverage types Because the superclass is not abstract, an instance of the superclass may consist of mixed types of CV_GeometryValuePair.

6.2 CV_DiscretePointCoverage

6.2.1 General

A discrete point coverage is characterized by a finite domain consisting of points. Generally, the domain is a set of irregularly distributed points. However, the principal use of discrete point coverages is to provide a basis for continuous coverage functions, where the evaluation of the continuous coverage function is accomplished by interpolation between the points of the discrete point coverage. Most interpolation algorithms depend upon a structured pattern of spatial relationships between the points. This requires either that the points in the spatial domain of the discrete point coverage be arranged in a regular way, or that the spatial domain of the continuous coverage be partitioned in a regular way in relation to the points of the discrete point coverage. Grid coverages Clauses 8 and 9 employ the first method; Thiessen polygon Clause 7 and TIN Clause 10 coverages employ the second. EXAMPLE A set of hydrographic soundings is a discrete point coverage.