Coordinate Reference Systems Geographic Coordinates

28 © 2016 Open Geospatial Consortium

1.7.2.2 Compression of other imagery datasets

In general, all TIFFGeoTIFF files benefit from LZW compression. For this reason, and as a general practice, the compression of all TIFF-based raster datasets is recommended. The one exception is when every cell in the raster dataset is a unique floating point number. In this case, the compressed file may be larger than the original.

1.7.2.3 Units of Measure

Requirement 7 http:opengis.netspecCDB1.0core uom All units of measure in a CDB conformant data store SHALL be in meters.

1.7.3 Coordinate Reference Systems

Requirement 8 http:opengis.netspecCDB1.0core crs Geographic locations in CDB SHALL be expressed usingWGS-84 World Geodetic System 1984, equivalent to EPSG European Petroleum Survey Group code 4326 2 dimensions and EPSG code 4979 3 dimensions. If a geographic location also has an altitude, the altitude SHALL be expressed relative to the WGS-84 reference ellipsoid. Please see the Volume 8: OGC CDB Spatial Reference System Guidance. Requirement 9 http:opengis.netspecCDB1.0core crs-client 29 © 2016 Open Geospatial Consortium Each implementation of the simulator client-devices accessing the CDB geospatial data SHALL at a minimum support the WGS-84 geodetic coordinate system as specified in Req 8 . Other reference systems may be used in the client application.

1.7.4 Geographic Coordinates

Requirement 10 http:opengis.netspecCDB1.0core coordinates Coordinates SHALL be described using the decimal degree format without the “°”symbol. The values of latitude and longitude SHALL be bounded by ±90° and ±180° respectively. Positive latitudes are north of the equator, negative latitudes are south of the equator. Positive longitudes are east of the Prime Meridian; negative longitudes are west of the Prime Meridian. Latitude and longitude are expressed in that sequence, namely latitude before longitude.

2. CDB Concepts

This chapter presents basic CDB data store model concepts. These concepts are either reused by other concepts or used repeatedly throughout the Standard. The CDB core data model may be viewed as an instance of a Discrete Global Grid System as defined in OGC 15-104. Please note, however, that the CDB data model and structure predates the OGC DGGS activity by over a decade and as such should not be deemed compliant with the OGC DGGS standard.. A DGGS is a spatial reference system that uses a hierarchical tessellation of cells to partition and address the globe. DGGS are characterized by the properties of their cell structure, geo- encoding, quantization strategy and associated mathematical functions. The following sections detail the CDB tiling storage model. Requirements Class - TilesGeocells and LoD relationships 11-16 and 41 req corecdb-structure-tiles-lod