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RE: updates to the Best Practice document

From: <Simon.Cox@csiro.au>
Date: Thu, 8 Sep 2016 03:43:18 +0000
To: <jeremy.tandy@gmail.com>, <public-sdw-wg@w3.org>
Message-ID: <8cb8c71ea8af4f64a573daeaf3467093@exch1-mel.nexus.csiro.au>
The recent revision of ISO 19109 added material on Coverages (as well as Observations) that was not in the original, recognising that coverages are important tools for some applications. You might also like to consider these sections from ISO 19109:2013

7.2.2 Coverages

Many aspects of the real-world may be represented as features whose properties are single-valued and static. These conventional features provide a model of the world in terms of discrete objects located in it. However, in some applications it is more useful to use a model focussing on the variation of property values in space and time, formalized as coverages. Users of geographic information may utilize both viewpoints. While coverages are themselves strictly features as well, it is common to contrast coverages and non-coverage features when discussing the functionality provided by each viewpoint. In the following discussion the name ‘feature’ refers to non-coverage features.

The feature and coverage representations may be related in several ways:

— signal processing to find and characterize features: signals in coverages may provide evidence for the existence, location and type of features, detected through modelling and interpretation;

EXAMPLE 1 Patterns of colour or other radiance bands within a remotely-sensed image may be used to infer the existence of specific objects or features on the ground.

EXAMPLE 2 Signals in a geophysical borehole log may be used to infer the presence of particular rock-units at underground locations.

— coverage-typed feature properties: feature properties whose value vary within the scope of a feature may be described as coverages whose domain extent is the geometry of the feature;

EXAMPLE 3 The variation of concentration of a particular ore-mineral within a mine may be described as a spatial function or coverage within the spatial limits of the mine.

— features sample a coverage: the values of a common property of a set of features provide a discrete sampling of a coverage, whose range type is the property, and whose domain is the aggregate geometry of the set of features.

EXAMPLE 4 The temperature at a set of weather stations may be compiled to show the spatial variation of temperature across the region where the stations are located.

A constraint in the latter two cases is that a property-type from a feature catalogue is the range-type of a coverage description in the same universe of discourse.

The case of features having property values that vary within the scope of the feature can be described using the general feature model (7.5.8).

While the coverage model is described in detail in ISO 19123, an application schema may include both feature- and coverage-types.
NOTE The feature and coverage viewpoints are related to (though not identical with) the so-called ‘vector’ and ‘raster’ approaches from traditional GIS implementations.

Then, immediately following:

7.2.3 Properties and observations

Property values are associated with features and coverages. In the case of features, a property value is associated with a classified object. In the case of coverages, a property value is associated with a position in the domain.


8.8 Rules for use of coverage functions

Coverage functions are used to describe characteristics of real-world phenomena that vary over space and/or time. Typical examples are temperature, elevation and precipitation. A coverage contains a set of such values, each associated with one of the elements in a spatial, temporal or spatio-temporal domain. Typical spatial domains are point sets (e.g. sensor locations), curve sets (e.g. contour lines), grids (e.g. orthoimages, elevation models), etc. A property whose value varies as a function of time may be represented as a temporal coverage or time-series. A continuous coverage is associated with a method for interpolating values at spatial positions between the elements of a domain, e.g. between two points or contour lines.

From: Jeremy Tandy [mailto:jeremy.tandy@gmail.com]
Sent: Thursday, 8 September 2016 7:17 AM
To: SDW WG Public List <public-sdw-wg@w3.org>
Subject: updates to the Best Practice document

Following today's BP call, I've now added into the BP doc what I was talking about:

* A section explaining about Coverages [1] (thanks to Jon Blower; I repurposed one of his Melodies blog posts!)
* The beginnings of a section that tries to provide a linear path through the decisions you might make when publishing data: "How to use these best practices" [2] ... this tries to combine SDW and DWBP best practices into a coherent whole ... that said, I've found it really hard to plan this out; I think it's working (& there's more in my head that I unfortunately don't have time to write before I disappear tomorrow ... leaving no more time for update before TPAC.

Hope these additions are worthwhile.


[1]: http://w3c.github.io/sdw/bp/#coverages

[2]: http://w3c.github.io/sdw/bp/#how-to-use

Received on Thursday, 8 September 2016 03:44:08 UTC

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