Control SRID through SDE

[CedricCorteel]

In order to query feature classes geographically via MS-SQL, it is crucial to use the SRID. Mapping features from one dataset into another is apparently only possible if SRID's (or better auth_SRID's) are identical. We can bypass this by getting XY-coordinates of a feature in one SRID and then project these coordinates in another SRID, but this is of course extra workload.

I know it is possible to create an SRID in SQL to avoid such problems, but most of our feature classes are created in ArcMAP/Catalog and thus SDE-controlled. Therefore we would like to know if there is already a way of controlling the SRID/auth_SRID through SDE (there has been a similar forum thread a while ago: http://forums.esri.com/thread.asp?t=249976&f=2291&c=158 )?

It would also be nice to get some more details on when to use SRID and when auth_SRID.

[RobertHu]

What versions of ArcSDE and ArcGIS are you using?

We had trouble to manage the srid for our FCs when we were in SDE 9.3.1. After upgrading to ArcSDE 10 and ArcGIS 10, it seems the only auth_srid matters. I think it is the spatial reference factorycode.

If you use SQL geometry, it doesn't matter what the srid is, as long as your FCs use same auth_srid, the SQL spatial functions/motheds will not fail. Whether it will give you the result you expect may still depend on other parameters (I am not 100 percent sure), such as falsex, falsey, etc.

Thanks!

[CedricCorteel]

Thanks a lot for your reply, Robert!

We are using 9.3.1. Also in 9.3.1, the auth_SRID is the most important one to refer to in SQL-queries, and it is of course that one we need to control.
If we upgrade to version 10, will we be able to control the auth_SRID then?

[RobertHu]

When we were in 9.3.1, we tried to modify the srid at table/FC level using SQL directly. It made the SQL spatial function, i.e. STIntersects, worked. But the FC's behavior in ArcCatalog became wired. That's a bigger issue we don't want to deal with. So we gave up that approach.

There were discussions about srid/auth_srid management in this forum. (Can't find the link anymore). One approach is roughly as create a feature dataset with the exact spatial reference you want at the begin. Then, while creating new FCs, ALWAYS define the spatial reference by referencing to the predefined FD. This is the method we use now.

Thanks!