- From: Little, Chris <chris.little@metoffice.gov.uk>
- Date: Thu, 4 May 2017 10:00:22 +0000
- To: Linda van den Brink <l.vandenbrink@geonovum.nl>, "Tandy, Jeremy" <jeremy.tandy@metoffice.gov.uk>
- CC: "public-sdw-wg@w3.org" <public-sdw-wg@w3.org>

1. Coordinate Reference System ISO TC211 defines: CRS:Coordinate System that is related to an object by a datum. Coordinate System: collection of coordinate Tuples related to the same coordinate reference system. Tuple: ordered list of values. Coordinate: one of a sequence of n numbers designating the position of a point in n-dimensional space. Datum: parameter or set of parameters that define the position of the origin, the scale, and the orientation of a coordinate system. 2. Conflating all these gives us a circular mess of CRS : collection of sequences of n numbers designating the position of a point in n-dimensional space that are related to an object by a parameter or set of parameters that define the position of the origin, the scale, and the orientation of a coordinate system. 3. ISO19111 Spatial Referencing by Coordinates and OGC Abstract Specification Topic 5 defines: Coordinate Reference System: coordinate system that is related to the real world by a datum. 4. We also have: SRS: system for identifying position in the real world. Presumably, the wavelength of a signal in the electromagnetic spectrum is part of a CRS but not a SRS. 5. ISO TC211 does not actually say that, usually in our case, the object is the Earth, giving a Geo-Spatial Reference System. 6. 'Dimension' is not ISO TC211 defined, but the usual definition is the inverse of a coordinate definition. 7. I also think that 'collection' implies a specific mathematical meaning, allowing an infinite number of elements, but is not defined. It is also implied that the tuples are all consistent and same 'type'. 8. I propose the following which is consistent with ISO: "Coordinate Reference System (CRS): A coordinate system to locate entities of interest with respect to an object using a datum. [[http://registry.it.csiro.au/sandbox/iso-tc211/terms/703|ISO TC211]] If the entities of interest and the object and datum are in the real world, the CRS is a Spatial Reference System (SRS). If the object is the Earth, the SRS is a Geo-Spatial Reference System (GRS). A GRS may be local, regional or global in scope. An example of a CRS that is not a SRS is the wavelength of a signal in the electromagnetic spectrum." 9. Then we need to add: "Datum: parameter or set of parameters that define the position of the origin, the scale, and the orientation of a coordinate system [[http://registry.it.csiro.au/sandbox/iso-tc211/terms/703|ISO TC211]]." Chris Little Co-Chair, OGC Meteorology & Oceanography Domain Working Group IT Fellow - Operational Infrastructures Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom Tel: +44(0)1392 886278 Fax: +44(0)1392 885681 Mobile: +44(0)7753 880514 E-mail: chris.little@metoffice.gov.uk http://www.metoffice.gov.uk I am normally at work Tuesday, Wednesday and Thursday each week

Received on Thursday, 4 May 2017 10:01:00 UTC