- From: <Will_Wilbrink@mapinfo.com>
- Date: Wed, 25 Jun 2008 15:05:11 -0400
- To: public-geolocation@w3.org
- Message-ID: <OF817F3F30.76D56CD2-ON85257473.00686892-85257473.0068D8C0@mapinfo.com>
Hello, I'm new to the mailing list, but do have some experience in this area. I was the co-chair of the OGC Open Location Services (OpenLS) specification: http://www.opengeospatial.org/standards/olscore and also worked with both LIF and subsequently OMA on the Mobile Location protocol (MLP): http://www.openmobilealliance.org/Technical/release_program/mlp_v31.aspx We decided to allow the default to be WGS 84. However, we also allowed an extension where a coordinate reference system could be specified. As pointed out earlier, many street databases are in other coordinate systems, so errors will occur with street matching if the two systems do not match. I contacted one of the staff members at OGC (Carl Reed) and asked for his input: In my experience with OASIS, IETF, OMA etc, every standard I have been involved in has specified WGS-84 2d as the default. That said, both OASIS and the IETF go into greater detail so that the reader has the proper context. The same is true for GeoRSS. The following are the typical words used in standards by other standards organizations that are using GML schema (or at least the ISO 19107 geometry model). Implementations shall support the following coordinate reference systems based on WGS 84. These are identified using the European Petroleum Survey Group (EPSG) Geodetic Parameter Dataset, as formalized by the following Open Geospatial Consortium (OGC) URNs: ? 3D: WGS 84 (latitude, longitude, altitude), as identified by the URN urn:ogc:def:crs:EPSG::4979. This is a three dimensional CRS. ? 2D: WGS 84 (latitude, longitude), as identified by the URN urn:ogc:def:crs:EPSG::4326. This is a two dimensional CRS. The most recent version of the EPSG Geodetic Parameter Dataset should be used. The CRS shall be specified using the above unversioned URN notation only; implementations do not need to support user-defined CRSs. Implementations MUST specify the CRS using the srsName attribute on the outermost geometry element. The CRS must not be respecified or changed for any sub-elements. The srsDimension attribute should be omitted, since the number of dimensions in these CRSs is known. The reason for a very clear expression of the CRS, even if WGS84 is the default, is to insure that there is interoperability across jurisdictional boundaries (including international). Regards, Will Wilbrink Pitney Bowes MapInfo Matt Womer <mdw@w3.org> Sent by: public-geolocation-request@w3.org 06/25/2008 01:40 PM To public-geolocation@w3.org cc Subject Re: The Geolocation API must provide location data in terms of a pair of latitude and longitude coordinates. Hi all, On Jun 25, 2008, at 1:09 PM, Erik Wilde wrote: > ...and please forgive me if i am not entirely correct in what i am > saying, i am not a GIS person. over the last year i have at least > learned that location is a more complex concept than i first thought > it would be. I'm glad to see these issues coming up. I'm hoping some of our geospatial technology experts will chime in here and give us some guidance. From past experience, things like the grid systems used in some countries, and the ellipsoidal coordinate systems used in others make interchange difficult when not knowing what each part of the system expects for a datum. (Similarly for timestamps, it should be noted that GPS time is not quite UTC.) -Matt
Received on Thursday, 26 June 2008 12:21:37 UTC