FAQ: What is Oracle Spatial geodetic data?
What is Oracle Spatial geodetic data?
With the release of Oracle 9i, Oracle introduced support specifically for geodetic coordinates. Geodetic coordinates are used to measure the surface of the Earth in terms of latitude and longitude. Oracle does not process Oracle Spatial geodetic data in the same way that it processes other data. There are some advantages and some limitations when you use geodetic data.
While using geodetic data does offer some advantages for some users, there are some important issues for users of ArcSDE with geodetic data should be aware of.
1. Circular arcs are not supported in lines or polygons.
2. Segments in line features cannot be longer than one half the circumference of the Earth.
3. Polygons cannot have an area greater than one half the area of the Earth’s surface.
4. Minimum bounding rectangles are not supported on geodetic data before Oracle 10g.
5. A line segments between vertices follow a great circle path, and not necessarily the straight line path shown on a flat display surface.
Please refer to the Oracle Spatial Users Guide and Reference for more information about geodetic data.
ArcSDE 8.2 Oracle Patch 1 was the first version of ArcSDE to process Oracle Spatial geodetic data differently than Oracle Spatial projected data.
Is your Oracle Spatial data geodetic?
Oracle Spatial data is considered geodetic if the well-known text (WKT) description of its coordinate system begins with the letters "GEOGCS". The WKT is associated with an Oracle Spatial feature through the Oracle Spatial Reference ID (SRID) stored in each feature and in USER_SDO_GEOM_METADATA. You can query an Oracle-provided table to find WKT for a given Oracle SRID (for example, 8307):
SELECT SRID, CS_NAME, WKTEXT
WHERE SRID = 8307;
You can also query for all SRIDs that refer to geodetic coordinate systems.
SELECT SRID, CS_NAME
WHERE WKTEXT LIKE 'GEOGCS%';