Sdo.intersection ... problems

Question

Hi all,
I use this simple query:
CREATE TABLE INTER2 AS
SELECT SDO_GEOM.SDO_INTERSECTION(G1.SHAPE, G2.SHAPE, 0.005) SHAPE
FROM RAIL G1, ROADS G2;
to find the intersections between these two layers. The first layer (rail) contains 47 lines and the second one (roads) 78 lines.
The new table that is constructed by running this query has 3666 rows (I think that this is because 78x47=3666) but when I visualize the layer in the spatial in the spatial index advisor I can see that only 40 points (intersections) exists.
So, I suppose that this query checks every possible pair from the two layers and creates a row which either has a point (intersection) in the shape column or has null value in this column.
My problem is that this layer cannot be inserted into ARCINFO (throught ARCSDE) because of its structure (every row must have a shape - geometry).
Can anyone tell me how can I perform this query and have as a result ONLY the rows with the points (intersections of the two layers)so I can visualize it in ARCINFO?
Thanks in advance

Answer 1

Hello John:
Seems like you are missing something from your query. I think it would help eliminate those records that do not return a SHAPE by using SDO_RELATE in your where clause. The query would look something like this:
CREATE TABLE INTER2 AS
SELECT SDO_GEOM.SDO_INTERSECTION(G1.SHAPE, G2.SHAPE, 0.005) SHAPE
FROM RAIL G1, ROADS G2
WHERE
MDSYS.SDO_RELATE(G1.SHAPE, G2.SHAPE, 'mask=ANYINTERACT querytype=WINDOW') = 'TRUE';
BUT - you may have to "trick" ArcSDE into recognizing the table (or should I say "feature class"). You may have to use an ArcSDE command to create the feature class, then go into SQL and drop the table. This has the effect of putting the correct metadata into the SDE schema tables, such as LAYERS and SPATIAL_REFERENCES. When you drop the table using SQL, the metadata will remain.
Then, use the CREATE TABLE... to create and populate the "feature class". Be sure to create a spatial index - we have found that you do not have to use the same name for the index as the one created by ArcSDE when you did the ArcSDE command to create the "feature class".
This trickery is necesarry because ArcSDE really prefers that EVERYTHING is created and populated via ArcSDE commands or ArcCatalog, but there are ways to "fool" the ESRI software.
Let me know if this helps.
R Clement
Alaska DNR