On 5/22/06, Martin Desruisseaux <[EMAIL PROTECTED]> wrote:
Adrian Custer a écrit : > Any chance you could write up a paragraph explaining what's going on > with axis order? I'm assembling notes for an eventual writeup of the > geotools CRS and this seems like an important corner case. The EPSG > CRS's are all in the lat, long order except for 4326 which is long, lat?Not exactly. In the EPSG database, the axis order is (latitude,longitude) for most geographic CRS, including EPSG:4326. The problem is that common usage in the field (derived from early WMS specification, as explained by Jody) expect (longitude,latitude) order, in violation of what EPSG said. EPSG:4326 was just cited as an example, but the problem apply to about all geographic CRS defined in the EPSG database. Axis order used in the field (from early OGC WMS specification) for "EPSG:4326" (and other geographic CRS) are in violation with the real axis order defined in the EPSG database. It has been proposed that "EPSG:4326" means "CRS with axis order as defined by OGC, not by EPSG", which seems to me a door opened for confusion since the CRS is called "EPSG:...", which suggest a CRS defined by the EPSG authority... An other problem is that "EPSG:4326" as defined by OGC would be inconsistent with usage of "4326" in the EPSG database itself (for example the "source" and "target" CRS relations in the "Coordinate_Operations" table). Martin.
There is clearly inconsistency between what EPSG database states and what OGC states. I would push this a bit further there is a discrepancy between EPSG database and most part of the data around the world (at least my world). Very often people ship data saying this is EPSG:4326, meaning lon,lat and not lat,lon. I would suggest the following two steps solution which should make everyone happy (or unhappy which would basically be the same :-) ). 1>Refactor OrderedAxisAuthorityFactory as follows: -Use a name similar to OGCOrderedAxisAuthorityFactory to state clearly what this is -Reorder CRS axes and operation axes for serving lon,lat data -Remove the code that actually strips off and/or changes metadata info like as EPSG:CODE from the returned crs or operation. This would be a short term solution. 2>Implement the based un URI as suggested by OGC (Jody would be able to provide more details than me) which would strictly follow the conventions found in the EPSG database. This would be a long term solution. I am sure there would many well-defined objections to these approaches, especially to the first one, but let me drop here below some considerations: A>The OrderedAxisAuthorityFactory would not be the default one therefore people willing to register it would at least be aware of the problem they aim to solve and hopefully they would be able to understand what they are doing. B>I know that NOT stripping the EPSG:CODE from a reordered crs would theoretically be incorrect. I get a CRS that claims to be EPSG:CODE but it is not. Correct. But as I stated in consideration 1, to get this behaviour I must have registered on purpose the OrderedAxisAuthorityFactory, therefore I should know what I am doing (hopefully)! C>99% of data in geographic WGS84 crs is lon,lat. D>Services (W*S) usually use codes like EPSG:4326 referring to lon,lat, ergo I would really love to avoid the axes swap when building envelopes and related objects! Simone.
------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmdlnk&kid0709&bid&3057&dat1642 _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
-- °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° Simone Giannecchini Software Engineer Freelance Consultant http://simboss.wordpress.com/ °°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°°° ------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid0709&bid&3057&dat1642 _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
