coverageFunction, CoverageFunctionType Coverage schema

Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 211 If the gml:coverageFunction property is omitted for a gridded coverage including rectified gridded coverages the gml:startPoint is assumed to be the value of the gml:low property in the gml:Grid geometry, and the gml:sequenceRule is assumed to be linear and the gml:axisOrder property is assumed to be ―+1 +2‖. EXAMPLE These defaults are best illustrated by a simple example as follows: AverageTempPressure xmlns=http:www.opengis.netapp xmlns:gml =‖http:www.opengis.netgml3.2‖ xmlns:xsi=http:www.w3.org2001XMLSchema-instance xsi:schemaLocation=http:www.opengis.netapp .CoverageExamples.xsd gml:domainSet gml:Grid dimension=2 gml:limits gml:GridEnvelope gml:low0 0gml:low gml:high4 4gml:high gml:GridEnvelope gml:limits gml:axisLabelsx ygml:axisLabels gml:Grid gml:domainSet gml:rangeSet gml:DataBlock gml:rangeParameters gml:CompositeValue gml:valueComponents Temperature uom=urn:x-si:v1999:uom:degreesCtemplateTemperature Pressure uom=urn:x-si:v1999:uom:kPatemplatePressure gml:valueComponents gml:CompositeValue gml:rangeParameters gml:tupleList3,101.2 5,101.3 7,101.4 11,101.5 13,101.6 17,101.7 19,101.7 23,101.8 29,101.9 31,102.0 37,102.1 41,102.2 43,102.3 47,102.4 53,102.5 59,102.6gml:tupleList gml:DataBlock gml:rangeSet AverageTempPressure Since no coverageFunction is specified the function is assumed to be that of linear scann ing with ―+1 +2‖ order starting at the location 0 0. If we look at the DataBlock, we see that we have the mapping shown in Table 4. 212 Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. Table 7 — Data block example Grid location Data value 0 0 3,101.2 1 0 5,101.3 2 0 7,101.4 3 0 11,101.5 0 1 13,101.6 1 1 17,101.7 2 1 19,101.7 3 1 23,101.8 0 2 29,101.9 1 2 31,102.0 2 2 37,102.1 3 2 41,102.2 0 3 43,102.3 1 3 47,102.4 2 3 53,102.5 3 3 59,102.6

19.3.12 CoverageMappingRule

gml:CoverageMappingRule provides a formal or informal description of the coverage function, per: element name=CoverageMappingRule type=gml:MappingRuleType substitutionGroup=gml:AbstractObject complexType name=MappingRuleType final=all choice element name=ruleDefinition type=string element name=ruleReference type=gml:ReferenceType choice complexType EXAMPLE MathML can be used for formal descriptions, informal ones may be any free text. The mapping rule may be defined as an inline string gml:ruleDefinition or via a remote reference through xlink:href gml:ruleReference. If no rule name is specified, the default is ‗Linear‘ with respect to members of the domain in document order.

19.3.13 GridFunction, GridFunctionType

gml:GridFunction provides an explicit mapping rule for grid geometries, i.e. the domain shall be a geometry of type grid. It describes the mapping of grid posts discrete point grid coverage or grid cells discrete surface coverage to the values in the range set. The content model is as follows: element name=GridFunction type=gml:GridFunctionType substitutionGroup=gml:AbstractObject complexType name=GridFunctionType sequence Copyright © 2007 Open Geospatial Consortium, Inc. All Rights Reserved. 213 element name=sequenceRule type=gml:SequenceRuleType minOccurs=0 element name=startPoint type=gml:integerList minOccurs=0 sequence complexType The gml:startPoint is the index position of a point in the grid that is mapped to the first point in the range set this is also the index position of the first grid post. If the gml:startPoint property is omitted the gml:startPoint is assumed to be equal to the value of gml:low in the gml:Grid geometry. Subsequent points in the mapping are determined by the value of the gml:sequenceRule.

19.3.14 sequenceRule, SequenceRuleType, SequenceRuleEnumeration

The sequenceRule is described by the content model: complexType name=SequenceRuleType simpleContent extension base=gml:SequenceRuleEnumeration attribute name=order type=gml:IncrementOrder attribute name=axisOrder type=gml:AxisDirectionList extension simpleContent complexType The gml:SequenceRuleType is derived from the gml:SequenceRuleEnumeration through the addition of an axisOrder attribute. The gml:SequenceRuleEnumeration is an enumerated type defined as: simpleType name=SequenceRuleEnumeration restriction base=string enumeration value=Linear enumeration value=Boustrophedonic enumeration value=Cantor-diagonal enumeration value=Spiral enumeration value=Morton enumeration value=Hilbert restriction simpleType These rule names are defined in ISO 19123. If no rule name is specified the default is “Linear”. The axisOrder attribute has the following content model: simpleType name=AxisDirectionList list itemType=gml:AxisDirection simpleType simpleType name=AxisDirection restriction base=string pattern value=[\+\-][1-9][0-9] restriction simpleType The value of a gml:AxisDirection indicates the incrementation order to be used on an axis of the grid. EXAMPLE 1 +3 means that the points in the grid are to be traversed from lowest to highest on the 3rd axis.