Feature and annotation styling

Copyright © 2006. Open Geospatial Consortium, Inc. All Rights Reserved. 9

6.7 Coordinate reference systems

Coverage geometries and the geometric properties of GML features and annotations include coordinates which are interpreted within the context of a coordinate reference system CRS. According to the rules of GML, the coordinate reference system is specified via URI. This URI may identify the CRS by reference to an authority and an authority maintained code. Alternatively, these URI may identify the physical location of a CRS definition. In those cases where an actual CRS definition is required, GML provides a grammar for encoding such coordinate reference systems. The coordinate reference system definitions encoded in GML can then be packaged with the JPEG 2000 data as for features etc. and referenced from the coverage description, or features, or can exist externally. This enables both network-centric and standalone implementations of GML in JPEG 2000 to be deployed. Some coordinate reference systems may require use of a GML coordinate reference system application schema. Mechanisms for referencing andor transporting GML application schemas are discussed in Clause 8.

6.8 Units of

measure Coverage values and properties of GML features and annotations may employ references to units of measure UOM. According to the rules of GML, the units are specified via URI. This URI may identify the UOM by reference to an authority and an authority maintained code. Alternatively, these URI may identify the physical location of a UOM definition. In those cases where an actual UOM definition is required, GML provides a grammar for the encoding of such units of measure. The units of measure definitions encoded in GML can then be packaged with the JPEG 2000 data as for features etc. and referenced from the coverage description, or features, or can exist externally. This enables both network-centric and standalone implementations of GML in JPEG 2000 to be deployed. Some units of measure may require use of a GML units of measure application schema. Mechanisms for referencing andor transporting GML application schemas are discussed in Clause 8. 7 Encoding rules for GML in JPEG 2000

7.1 Introduction

This section describes specific rules that SHALL be followed when encoding GML data for use within JPEG 2000 files. All GML instance data associated with a specific codestream is contained in a single GML feature collection called the codestream specific feature collection, which contains the following: a GML Coverage objects ONE only. 10 Copyright © 2006. Open Geospatial Consortium, Inc. All Rights Reserved. b GML Features zero or more. c GML annotations zero or more, see Clause 9. These may appear in any order in the codestream specific feature collection i.e. there is no requirement that the coverage object be first. All codestream specific feature collections are feature members of a top-levelroot GML feature collection see Clauses 8.1, 8.2. The top-levelroot feature collection may also contain as a feature member, a collection of feature instances that are associated to ALL JPEG 2000 codestreams. GML metadata is referenced through the gml:metaDataProperty which is attached to one or more of the objects as above. GML default styles are referenced through the gml:defaultStyle property which is attached to one or more of the objects as above. Instance data for units of measure and coordinate reference system definitions may be optionally provided. This shall be contained in a Dictionary file which SHALL be valid against the GML dictionary.xsd. The GML version of instance data can be determined by referencing a retrievable schema document; the schema documents required to validate an instance shall be retrievable.

7.2 Coverage description

GML Coverage Descriptions define the associated JPEG 2000 file as a geographic image. Such coverage descriptions are based directly on the GML coverage.xsd or through the use of a GML application schema that imports directly or indirectly coverage.xsd. There can be only ONE coverage description instance per codestream, and only ONE coverage description per codestream specific FeatureCollection. Furthermore, each coverage description SHALL use gml:RectifiedGrid as its domain. Clause 8.2 provides details on the mapping of coverage description instances and codestreams in the multiple codestream case. The following is an example coverage description: exp1:AverageTemp dimension = 2 gml:id = AT0001 gml:rectifiedGridDomain gml:RectifiedGrid dimension = 2 gml:limits gml:GridEnvelope gml:low 1 1 gml:low gml:high 4 4 gml:high gml:GridEnvelope gml:limits gml:axisName x gml:axisName gml:axisName y gml:axisName gml:origin gml:Point gml:id = P0001 srsName = gmljp2:xmlcrs.gmlcrs1123