| | 35 | |
| | 36 | '''Coordinate System Handling''' |
| | 37 | |
| | 38 | Once you create a data store, you create and apply a schema to it. The schema defines the table and columns into which you will put data. For FDO geometry properties, there are two possible SQL Server spatial column types: geometry and geography. The geography type is used for geodetic (lat/long) coordinate systems and the geometry type is used for non-geodetic coordinate systems. For both, a spatial index with default parameters is created automatically. |
| | 39 | |
| | 40 | SQL Server 2008 includes a catalog of geodetic coordinate systems, but not non-geodetic coordinate systems. Both geometry and geography column types save SRID values, but only geography type columns reference an entry in the catalog, and in this case the SRID numbers are EPSG numbers. |
| | 41 | Some applications will require that the provider returns a valid WKT for the corresponding coordinate system. Since for some coordinate systems, this information is not directly available from the SQL Server 2008 catalog, a mechanism was added to by-pass this problem. |
| | 42 | |
| | 43 | To translate the coordinate to an SRID to use in SQL Server, the provider uses a translation table in a file called ExtendedCoordSys.txt, which resides in the com sub-folder of the FDO installation directory (usually FDO\bin\com\ExtendedCoordSys.txt). If the coordinate systems are in the file, the coordinate system will be recognized and handled by the FDO Provider for SQL Server Spatial. |
| | 44 | |
| | 45 | Note: If the coordinate system has an EPSG code, use that code as the SRID. Otherwise, use an SRID that is not an EPSG code. |
| | 46 | |
| | 47 | The ExtendedCoordSys.txt is composed of the following information (it can be copied and pasted into the file directly as // represent comments) |
| | 48 | |
| | 49 | // [[BR]] |
| | 50 | //The format for each line in this file is:[[BR]] |
| | 51 | //[[BR]] |
| | 52 | // <SRID> <Coordinate System Name> <WKT>[[BR]] |
| | 53 | //[[BR]] |
| | 54 | // where:[[BR]] |
| | 55 | // SRID: is the SRID for each coordinate system. For all coordinate systems initially in the file, the SRID[[BR]] |
| | 56 | // is the coordinate system's EPSG number.[[BR]] |
| | 57 | //[[BR]] |
| | 58 | // Coordinate System Name: the coordinate system name. [[BR]] |
| | 59 | //[[BR]] |
| | 60 | // WKT: a string in Open Geospatial Well-Known Text format. [[BR]] |
| | 61 | //[[BR]] |
| | 62 | // Only Geodetic or Projected coordinate systems can be listed so the WKT must start with either GEOGCS or [[BR]] |
| | 63 | // PROJCS. [[BR]] |
| | 64 | //[[BR]] |
| | 65 | // Each field must be separated by spaces (sorry, no tabs). [[BR]] |
| | 66 | //[[BR]] |
| | 67 | // Coordinate System Name can have embedded spaces (though this is probably unlikely). All words after the EPSG number,[[BR]] |
| | 68 | // up to before the WKT, are treated as part of the Coordinate System name. [[BR]] |
| | 69 | //[[BR]] |
| | 70 | // The file must reside in the FDO com directory (A sub-directory named 'com' that is in the same directory as the [[BR]] |
| | 71 | // SQLServerSpatial provider DLL). [[BR]] |
| | 72 | //[[BR]] |
| | 73 | |
| | 74 | |
| | 75 | |
