Jody Garnett wrote: > Farrukh Najmi wrote: >> Thanks Jody for the very helpful response. > No worries; now if you can tell me where to put that information in > the user guide for the next person we will be ahead of the game :-) > Where would you look ...
It should probably be under Chapter 03 JTS Topology Suite perhaps under a page titled "Relationship Between JTS Coordinate System and Geotools CoordinateReferenceSystem" or some such. In http://docs.codehaus.org/display/GEOTDOC/01+How+to+Create+a+Geometry it should be clarified that SRID has no signficance when creating a GeometryFactory. Otherwise it seems as if the GeometryFactory uses specified SRID and corresponding CRS for its create operations. >> I am unclear about one important conceptual understanding though. You >> said that "JTS does not care (or use) the SRID value". So what does >> JTS use for its internal CoordinateReferenceSystem? Does that mean >> that before geometry objects are stored using JTS they are normalized >> to that JTS internal CoordinateReferenceSystem? How else could JTS do >> spatial operations on geometry objects that use different SRID values? > Just so; there is a JTS utility class here to help you reproject your > JTS Geometry into the CoordinateReferneceSystem of your choice. > - http://docs.codehaus.org/display/GEOTDOC/02+JTS+Utility+Class What CRS does geotools use internally to normalize all geometry instances before storing? >> Said another way, geotools allows apps to use a large number of >> CoordinateReferenceSystems among different geometry objects. I had >> assumed JTS did the same and the only difference between the two was >> use of SRID vs. CoordinateReferenceSystem with some mapping between >> the two. Your statement "JTS does not care (or use) the SRID value" >> puts in doubt my understanding of how CoordinateReferenceSystems are >> handled in the two libraries. > JTS does the mathematical "topology part"; see this page: > http://docs.codehaus.org/display/GEOTDOC/Point+Set+Theory+and+the+DE-9IM+Matrix > > > GeoTools does the mathematical "referencing part", and the features, > and the rendering and the xml and the database access and the .... > well we try and get the job done. > Sounds like a good division of labor :-) Thanks for bearing with me my many perhaps basic questions. -- Regards, Farrukh Najmi Web: http://www.wellfleetsoftware.com ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
