Tuesday, February 21, 2012

Merging Geometry boundaries using Oracle spatial

Some times there is a requirement to merge two or more boundaries/borders into one, such as a custom region/territory. For eg. you may need to merge California, Oregon and Washington which are the states that comprise the Western US region. 

In  order to achieve this, I assume that you already have the state boundaries for California, Oregon and Washington. If not, you can get it easily on otn, that includes the standard boundaries. in the world_sample schema. Once you have this information you can use the Oracle Spatial function SDO_AGGR_UNION. Hence, you can combine several standard boundaries into a new region.

Below is an way how you would merge the states mentioned above into a new custom Western US region.

INSERT INTO custom_area 
SELECT 'Western US', SDO_AGGR_UNION(SDOAGGRTYPE(o.geometry, 0.5)) FROM wom_area WHERE iso_country_code = 'USA' and feature_type = 909996 and name in ('CALIFORNIA', 'OREGON', 'WASHINGTON');

Here, the SDOAGGRTYPE is an object that specifies the geometry column from the spatial table wom_area and the dimensional array.

Create the Geometry columns in Oracle Database

Many times we have the Geo location related information as latitude and longitude. In order to plot these on the maps using mapviewer in OBIEE we need to convert these into spatial data which is a option available with the oracle database. In this entry we will look at how to convert the lat/lon information into Oracle Spatial data.

1. Create the Geometry columns in Oracle Database
a. Based on the latitude/longitude information that is available create Geometry column
b. Insert Geometry based columns in metadata tables (USER_SDO_GEOM_METADATA)
c. Create a spatial index
Let’s look at each of these steps in detail, with the help of an example. As mentioned earlier, the assumption is that the data we get from the customer has information on latitude and longitude. If the data that the customer provides does not have latitude-longitude information, the flow will change slightly to use the spatial capabilities of the database to convert the address into latitude and longitude.

 Step 1: Create the Geometry Columns in the Database
 There are two columns latitude and longitude that need to be available to be able to use the spatial capabilities of the Oracle Database.

1. Alter the table to create the Geometry column. In the example below, we create a column called store_geo in the “store” table

alter table store add (store_geo sdo_geometry);
2. Populate the new column using the following query:

update store set store_geo = MDSYS.SDO_GEOMETRY(2001, 8307, MDSYS.SDO_POINT_TYPE (longitude, latitude,NULL),NULL,NULL);

3. Check if the column has been populated correctly:

4. Update the spatial metadata table with the details for the new geometry column created

VALUES ('store', 'store_geo',
(MDSYS.SDO_DIM_ELEMENT('LONG', -180.0, 180.0, 0.005),
MDSYS.SDO_DIM_ELEMENT('LAT', -90.0, 90.0, 0.005)

5. Create the spatial index on the geometry column

DROP INDEX store_idx;
CREATE INDEX store_idx ON store(store_geo);
INDEXTYPE IS mdsys.spatial_index;