View source for ISO 19123:2005 Geographic information - Schema for coverage geometry and functions

==Overview==
{| class="wikitable"
| Full name
| [http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=40121 ISO 19123:2005, Geographic information – Schema for coverage geometry and functions]
|-
| Version
| Edition 1
|-
| Amendments
| None
|-
| Corrigenda
| None
|-
| Published by
| ISO/TC 211
|-
| Languages
| English
|-
| Online overview
| https://www.iso.org/obp/ui/#iso:std:iso:19123:ed-1:v1:en
|-
| Type of standard
| ISO International Standard <br/> Meta level
|-
| Related standard(s)
| [http://wiki.icaci.org/index.php?title=Spatial_schema ISO 19107:2003, Geographic information – Spatial schema] <br/> [http://wiki.icaci.org/index.php?title=Rules_for_application_schema ISO 19109:2005, Geographic information – Rules for application schema] <br/> ISO 19110 <br/> [http://wiki.icaci.org/index.php?title=Spatial_referencing_by_coordinates ISO 19111:2007, Geographic information – Spatial referencing by coordinates] <br/> [http://wiki.icaci.org/index.php?title=Metadata_Fundamentals ISO 19115:2003, Geographic information – Metadata ]<br/> [http://wiki.icaci.org/index.php?title=Metadata_%E2%80%93_Part_2:_Extensions_for_imagery_and_gridded_data9 ISO 19115-2:2009, Geographic information – Metadata – Part 2: Extensions for imagery and gridded data] <br/>  ISO 19118:2011, Geographic information – Encoding <br/>  [http://wiki.icaci.org/index.php?title=Imagery,_gridded_and_coverage_data_framework ISO 19121:2000, Geographic information – Imagery and gridded data] <br/>  ISO 19129:2009, Geographic information – Imagery, gridded and coverage data framework
|-
| Application
| This standard provides the conceptual schema for the spatial aspects of coverages, which includes all forms of imagery, gridded and raster data, such as remote sensing, photogrammetry, image processing, digital elevation and terrain models and modelling using discrete surfaces (polygons with homogenous values) or continuous surfaces.
|-
| Conformance classes
| Simple coverage interface <br/> Discrete coverage interface <br/> Thiessen polygon coverage interface <br/> Quadrilateral grid coverage interface <br/> Hexagonal grid coverage interface <br/> TIN coverage interface <br/> Segmented curve coverage interface <br/> Discrete coverage interchange <br/> Thiessen polygon coverage interchange <br/> Quadrilateral grid coverage interchange <br/> Hexagonal grid coverage interchange <br/> TIN coverage interchange <br/> Segmented curve coverage interchange
|-
| Fundamental geospatial dataset
| Category: Base geography <br/> Data Theme: Rectified imagery
|}

==Scope==
ISO 19123:2005 defines a conceptual schema for the spatial characteristics of coverages. Coverages support mapping from a spatial, temporal or spatiotemporal domain to feature attribute values where feature attribute types are common to all geographic positions within the domain. A coverage domain consists of a collection of direct positions in a coordinate space that may be defined in terms of up to three spatial dimensions as well as a temporal dimension. Examples of coverages include rasters, triangulated irregular networks, point coverages and polygon coverages. Coverages are the prevailing data structures in a number of application areas, such as remote sensing, meteorology and mapping of bathymetry, elevation, soil and vegetation. This International Standard defines the relationship between the domain of a coverage and an associated attribute range. The characteristics of the spatial domain are defined whereas the characteristics of the attribute range are not part of this standard.

==Implementation benefits==
ISO 19123:2005 provides a comprehensive explanation of coverages and on that basis alone is an excellent reference work for anyone dealing with imagery, gridded, raster or any other type of coverage data. Formally, a coverage is a “feature that acts as a function to return values from its range for any direct position within its spatial, temporal or spatiotemporal domain”. In practice, this means that a coverage includes all the different types of imagery, gridded and raster data. This is because all these types of data have some or all of their non-spatial attributes being associated with their spatial attributes (i.e. with positions in the coverage), depending on the coverage’s function or rules. A coverage could have a regular or irregular distribution of non-spatial attribute values.

The key difference between all these types of coverage data and a vector-type feature is that with a vector-type feature, the spatial and non-spatial attributes are independent of one another. For example, while a non-spatial attribute (say, its official name) might be homogenous for the whole of a vector-type feature, a non-spatial attribute of a coverage (say, the strength of reflectance in a particular radiometric frequency band) might vary throughout the feature, depending on where it is in the feature. In other words, each pixel (or grid cell or point) in the coverage has both a position and a set of one or more values. Depending on the nature of the coverage, the position of each point is given explicitly (as for a triangulated irregular network), or determined as an offset from the origin of the coverage (as for a regular grid). Similarly, the boundary of the coverage might be its convex hull or might be specified by a clip area.

ISO 19129:2009, Geographic information – Imagery, gridded and coverage data framework, '''(see Table 10.39)''' draws heavily on ISO 19123:2005, with the key difference being that ISO 19129:2009 provides a framework for understanding the various formats for encoding coverages and template application schemas for different types of imagery and gridded data. 

==Implementation guidelines==
ISO 19123:2005 is not implemented directly: rather, it is implemented through other standards, such as ISO 19129:2009 '''(see Table 10.39)''', or in application schemas. The primary purpose of ISO 19123:2005 is to define the conceptual schema for the spatial characteristics of the different types of coverage data. The standard also describes the domain of a coverage (the direct positions or locations in the coverage), the range of a coverage (the attribute values), interpolation methods and sequential enumeration for various types of coverages. There are two main types of coverage:

*'''Discrete''': typically this is a set of polygons with the attributes of each polygon relating to every point within that polygon. Note that the polygons could overlap one another and/or there could be gaps between polygons. A discrete coverage could actually consist of any finite set of geometric objects. A typical example is a classified, geocoded satellite image. The five types of discrete coverage described in ISO 19123:2005 are:

:*'''Discrete point coverage''': typically a set of irregularly distributed points used for creating continuous coverage functions, such as the points in a TIN.
:*'''Discrete grid coverage''': A finite set of points in a grid.
:*'''Discrete curve coverage''': A finite set of curves or lines that are typically elements in a network. Essentially, this is a raster representation of a network.
:*'''Discrete surface coverage''': A finite set of surfaces that are typically mutually exclusive and that partition the extent of the coverage exhaustively, that is, they provide continuous coverage but do not overlap one another. A special case of a discrete surface coverage is a typical polygon coverage, which is where the surfaces are flat and parallel with the surface of the Earth.
:*'''Discrete solid coverage''': A finite set of solids. An example would be flight paths, air corridors, and other uncontrolled, controlled, restricted and prohibited air spaces modelled as three-dimensional objects (solids).

*'''Continuous''': typically these are attribute values that vary across space, as is commonly found in an unclassified image. More formally, it is a coverage containing a set of direct positions, each of which has its own attribute values. Another typical example of a continuous coverage is a dataset that has been interpolated from a set of measurements scattered throughout the area (e.g. kriging from borehole data) or that has been generated by running models (e.g. weather forecasting). The six types of continuous coverage described in ISO 19123:2005 are described in detail in the standard, but briefly they are:

*'''Thiessen polygon coverage''': all the points inside one Thiessen polygon (or Voronoi or Dirichlet polygon or tessellation) are closer to the centre (or seed or generator) of that polygon than to the centre of any other polygon. The boundaries between two neighbouring polygons are then the perpendicular bisector of the line joining their centres. However, it is also possible to have weighted Thiessen polygons, to use distances other than the direct, Euclidian distance between two centres, or to have fuzzy boundaries between polygons.

*'''Quadrilateral grid coverage''': a regular tessellation on a square, rectangular, parallelogram or parallelepiped grid. An example of a parallelogram coverage would be an uncorrected image from a push-broom type satellite-based sensor, with each row being offset due to the rotational geometry of the satellite.

*'''Hexagonal grid coverage''': a regular tessellation on a hexagonal grid. It can be converted easily into a parallelogram grid.

*'''Triangulated irregular network (TIN) coverage''': the structure of the TIN is determined by GM_TIN, which is defined in ISO 19107:2003, Geographic information – Spatial schema. Specifically, GM_TIN specifies the stop lines (questionable local continuity, which a triangle side shall not cross), break lines (local ridges or depressions that shall become triangle sides), maximum length of a triangle side, and the control points (posts or triangle corners).

*'''Segmented curve coverage''': lines or curves (typically in a network) along which attribute values vary continuously or discontinuously. An example with a continuously varying attribute would be traffic volume on a road network, while an example of a discontinuously varying attribute would be the posted speed limit on a road network.

As can be gathered, some vector datasets could be represented directly as coverages, for example, representing buildings as a discrete solid coverage or a road network as a discrete curve coverage. Further, some datasets could be represented as a discrete coverage or as a continuous coverage generated from the discrete coverage.

Each coverage has the attributes domainExtent (its extent in space, time or space-time), rangeType (attributes and their data types) and commonPointRule (the method for determining the attribute value along a polygon boundary or between grid points). Each coverage has five operations that specify how to list, select, find, evaluate and evaluate inverse (determine the locations where an attribute value occurs) the attributes of the coverage.

'''Annex B''' describes the UML notation used in the ISO/TC 211 standards. Initially, such an annex was common in the ISO/TC 211 standards, but it is now omitted because ISO 19103:2005 '''(see Table 10.7)''' describes the conceptual schema language used in the standards. '''These annexes''' make the standards more expensive (price is determined by the number of pages). '''Annex C''' describes nine types of interpolation methods, three for segmented curve coverages, namely linear interpolation, quadratic interpolation and cubic interpolation; three for quadrilateral grid coverages, namely bilinear interpolation, biquadratic interpolation and bicubic interpolation; one for Thiessen polygon and hexagonal grid coverages, namely lost area interpolation; one for TIN coverages, namely barycentric interpolation; and one for all types of coverages, namely nearest neighbour interpolation. '''Annex D''' describes six types of sequential enumeration: linear scanning, boustrophedonic scanning, Cantordiagonal (or zigzag) scanning, spiral scanning, Morton order, Hilbert order and interleaving of feature attribute values.