Spatial SQL query showing parcels containing centroid of building

Question

I am trying to write a query that selects parcels that contain the centroid of a certain building code (bldg_code = 3).

The parcels are listed in the table "city.zoning" and contains a column for a PIN, geometry, and area of each parcel. The table "buildings" contains a column for bldg_type and bldg_code indicating the building type and its corresponding code. The building type of interest for this query has a bldg_code of 3.

So far I've developed a query that shows parcels that interact with the building type of interest:

select a.*
from city.zoning a, username.buildings b
where b.bldg_code = 3 and sdo_anyinteract(a.geom,b.geom) = 'TRUE';

Any ideas?

Answer 1

You can use SDO_GEOM.SDO_CENTROID (documentation) to find the centroid of a geometry.

Note that the centroid provided by this function is the mathematical centroid only and may not always lie inside the geometry, for example, if your polygon is L shaped. SpatialDB Adviser has a good article on this, but here's a quick illustration:

If this isn't a problem for you and you don't need that level of accuracy, just use the built-in, but if you do consider this to be a problem (as I did in the past), then SpatialDB Adviser has a standalone PL/SQL package that corrrectly calculates centroids.

Depending on your performance needs, you could calculate the centroids on-the-fly and just use them in your query directly, or alternatively, add a centroid column to the table and compute and cache the values with application code (best case) or trigger (worst case).

Your query would look something like this:

SELECT a.*
FROM city.zoning a
JOIN username.buildings b ON sdo_contains(a.geom, b.centroid) = 'TRUE'
WHERE b.bldg_code = 3  

Note that this is using SDO_CONTAINS on the basis of the a.geom column being spatially indexed and a new column b.centroid that has been added and populated (note - query not tested). If the zoning geometry is not spatially indexed, then you would need to use SDO_GEOM.RELATE, or index the centroid column and invert the logic to use SDO_INSIDE.