General interpolationType CV_HexagonalGridCoverage

Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 48

9.2.3 locate

The operation locate p: DirectPosition: CV_ValueHexagon is inherited from CV_ContinuousCoverage with the restriction that it shall return a CV_ValueHexagon. It shall accept a DirectPosition as input and return the CV_ValueHexagon that contains that DirectPosition. Figure 21 — CV_HexagonalGridCoverage

9.2.4 evaluate

The operation evaluate p: DirectPosition, list: Sequence CharacterString: Record is inherited from CV_Coverage. Evaluation of a CV_HexagonalGridCoverage involves two steps. The first is to find the CV_ValueHexagon that contains the input DirectPosition; the second is to interpolate the feature attribute values at the DirectPosition from the CV_GridPointValuePairs at the centres of the surrounding CV_ValueHexagons. Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 49

9.2.5 CoverageFunction

The association CoverageFunction shall link this CV_HexagonalGridCoverage to the set of CV_ValueHexagons of which it is composed.

9.2.6 ControlPoints

The association ControlPoints shall link the CV_HexagonalGridCoverage to the CV_GridValuesMatrix for which it is an evaluator.

9.3 CV_GridValuesMatrix

CV_GridValuesMatrix is documented in 8.14, but is specialized by four constraints: a It is a CV_RectifiedGrid. b source.dimension = 2 The inherited attribute dimension has a value of 2. c source Direction of offsetVectors differ by 60 degrees The offsetVectors differ in direction by 60 degrees. d source,offsetVector[1].length = source.offsetVector[2].length The lengths of the offsetVectors are equal.

9.4 CV_ValueHexagon

9.4.1 General

CV_ValueHexagon is a subclass of CV_ValueObject.

9.4.2 geometry

The attribute geometry: GM_Polygon shall hold the geometry of the CV_ValueHexagon centred on the CV_GridPointValuePair identified by the association Control.

9.4.3 Control

The association Control shall link this CV_ValueHexagon to the CV_GridPointValuePair at its centre. 10 Triangulated irregular network TIN coverages

10.1 General

The basic idea of a TIN is to partition the convex hull of the points in the domain of a discrete point coverage into a computationally unique set of non-overlapping triangles. Each triangle is formed by three of the points in the domain of the discrete point coverage. The Delaunay triangulation method is commonly used to produce TIN tessellations with triangles that are optimally equiangular in shape, and are generated in such a manner that the circumscribing circle containing each triangle contains no point of the discrete point coverage other than those at the vertices of the triangle Figure 22. GM_TIN ISO 19107:2003 describes a Delaunay triangulation.