Oracle8 Spatial Cartridge User's Guide and Reference Release 8.0.4 A5326402 

This chapter contains descriptions of the tuning functions and procedures shown in Table 61
This function estimates the appropriate tiling level to use when indexing with fixedsize tiles.
SDO_TUNE.ESTIMATE_TILING_LEVEL (layername, maxtiles, type_of_estimate)
The function returns an integer representing the level to use when creating a spatial index for the specified layer.
The SDO_ADMIN.POPULATE_INDEX() and SDO_ADMIN.UPDATE_INDEX() procedures are used to create or update the spatial index using fixedsize or variablesized tiles. Store the value returned by the SDO_TUNE.ESTIMATE_TILING_LEVEL()
function in the SDO_LEVEL column of the <layername>_SDOLAYER table prior to building the spatial index.
The maxtiles parameter specifies the maximum number of tiles that should be used to define a grid covering the rctangular extend of interest. This extent could be:
SDO_TUNE.EXTENT_OF()
procedure)
The code shown in Example 61 generates a recommendation based on the extent of the defined coordinate system (90 to +90 latitude and 180 to +180 longitude). This example returns a level whose tiles are not smaller than one degree cells.
set serveroutput on declare tiling_level integer; begin tiling_level := mdsys.sdo_tune.estimate_tiling_level('WORLD_CITIES',
360*180, 'LAYER_EXTENT'); dbms_output.put_line('VALUE is ' tiling_level); end;
For many applications, however, it is more effective to call the SDO_TUNE.ESTIMATE_TILING_LEVEL() function using the ALL_GID_EXTENT estimate type. In Example 62, assume the dataset consists of block groups for San Francisco and that the <layername>_SDODIM table defines the extent to be one that covers all of California. Because the dataset is localized to a small subregion of this extent, ALL_GID_EXTENT is the appropriate estimate type. The recommended tiling level in this case will be such that at most 10,000 tiles will be required to completely cover the extent of San Francisco block groups.
set serveroutput on declare tiling_level integer; begin tiling_level:= mdsys.sdo_tune.estimate_tiling_level('SF_BLOCK_GROUPS',
10000, 'ALL_GID_EXTENT'); dbms_output.put_line('VALUE is' , tiling_level); end;
The third type of estimate helps determine the tiling level that should be used such that on average, the maxtiles parameter defines the number of tiles to cover the extent of a single geometry in the layer. This estimate type requires the most computation of the three because the bounding box of every geometry is used in calculating the average extent. In Example 63, eight tiles on average are used to cover any block group in San Francisco.
set serveroutput on declare tiling_level integer; begin tiling_level := mdsys.sdo_tune.estimate_tiling_level('SF_BLOCK_GROUPS', 8,
'AVG_GID_EXTENT'); dbms_output.put_line('Tiling level value is '  tiling_level); end;
This procedure determines the extent of all geometries in a layer.
SDO_TUNE.EXTENT_OF (layername, min_X, max_X, min_Y, max_Y)
This procedure returns the coordinates of the minimumbounding rectangle for all geometric data in a layer. The data type is NUMBER for the four return values.
None