Relationship with ISO 19123 The coverage model and representations

Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 203 complexType name=GridLimitsType sequence element name=GridEnvelope type=gml:GridEnvelopeType sequence complexType complexType name=GridEnvelopeType sequence element name=low type=gml:integerList element name=high type=gml:integerList sequence complexType The gml:low and gml:high elements are each gml:integerLists, which are coordinate tuples, the coordinates being measured as offsets from the origin of the grid along each axis, of the diagonally opposing corners of a ―rectangular‖ region of interest. EXAMPLE The following example illustrates a simple Grid. gml:Grid dimension=2 gml:limits gml:GridEnvelope gml:low0 0gml:low gml:high3 3gml:high gml:GridEnvelope gml:limits gml:axisLabelsx ygml:axisLabels gml:Grid In this example the Grid has posts points at locations 0,0, 0,1,1,0,1,1 through to 3,3. When a grid point is used to represent a sample space e.g. image pixel, the grid point represents the center of the sample space see ISO 19123:2005, 8.2.2.

19.2.3 RectifiedGrid

A rectified grid is a grid for which there is an affine transformation between the grid coordinates and the coordinates of an external coordinate reference system. It is defined by specifying the position in some geometric space of the grid ―origin‖ and of the vectors that specify the post locations. gml:RectifiedGrid implements ISO 19123 CV_RectifiedGrid see D.2.11 and ISO 19123:2005, 8.9 and is declared as follows: element name=RectifiedGrid type=gml:RectifiedGridType substitutionGroup=gml:Grid complexType name=RectifiedGridType complexContent extension base=gml:GridType sequence element name=origin type=gml:PointPropertyType element name=offsetVector type=gml:VectorType maxOccurs=unbounded sequence extension complexContent complexType Note that the grid limits post indexes and axis name properties are inherited from gml:GridType and that gml:RectifiedGrid adds a gml:origin property contains or references a gml:Point and a list of gml:offsetVector properties specified using gml:VectorType as its data type as described in 10.1.4.5.