Oracle7 Spatial Data Option User's Guide and Reference Go to Product Documentation Library
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Tuning Functions


This chapter contains descriptions of the tuning functions and procedures shown in Table 6-1:

Table 6-1 Tuning Functions:

Function   Description  

SDO_TUNE.ESTIMATE_TILING_LEVEL

 

Determines an appropriate tiling level for creating fixed-size index tiles.

 

SDO_TUNE.EXTENT_OF

 

Determines the minimum bounding rectangle of the data in a layer.

 

SDO_TUNE.ESTIMATE_TILING_LEVEL

Purpose

This function estimates the appropriate tiling level to use when indexing.

Syntax

SDO_TUNE.ESTIMATE_TILING_LEVEL (layername, maxtiles, type_of_estimate)

Keywords and Parameters

layername

 

Specifies the name of the data set layer to examine. Data type is VARCHAR2.

 

maxtiles

 

Specifies the maximum number of tiles that can be used to index the rectangle defined by the type_of_estimate parameter. Data type is INTEGER.

 

type_of_estimate

 

Indicates by keyword one of three different models. Specify the type of estimate with one of the following keywords:

LAYER_EXTENT -- Use the rectangle defined by your coordinate system. ALL_GID_EXTENT -- Use the minimum bounding rectangle that encompasses all the geometric objects within the layer. AVG_GID_EXTENT -- Use a rectangle representing the average size of the individual geometries within the layer. This option performs the most analysis of the three types.  

Returns

The procedure returns an integer representing the level to use when creating a spatial index for the specified layer.

Usage Notes

The SDO_ADMIN.POPULATE_INDEX and SDO_ADMIN.UPDATE_INDEX procedures are used to create or update the spatial index using fixed or variable-sized tiles. Store the value returned by the estimate_tiling_level() function in the sdo_level column of the <layername>_SDOLAYER table prior to building the spatial index.

For many applications, it is effective to call the estimate_tiling_level() function using the ALL_GID_EXTENT estimate type and a maximum of 10,000 tiles, as shown in Example 6-1.

Example 6-1 Recommend Tile Level Based on the GIDs of All Geometries

set serveroutput on
declare
   lev integer;
begin
   lev:=   mdsys.sdo_tune.estimate_tiling_level('SF_BLOCK_GPS',10000,
'ALL_GID_EXTENT'); dbms_output.put_line('VALUE is' ,|| lev); end;

The code shown in Example 6-2 generates a recommendation based on the extent of the defined coordinate system (latitude and longitude). This example returns a level whose tiles are not smaller than one degree cells.

Example 6-2 Recommend Tile Level for One-Degree Lat/Lon Cells

set serveroutput on
declare
   lev integer;
begin
   lev := mdsys.sdo_tune.estimate_tiling_level('WORLD_CITIES', 360*180,
'LAYER_EXTENT'); dbms_output.put_line('VALUE is '|| lev); end;

Related Topics


SDO_TUNE.EXTENT_OF

Purpose

This procedure determines the extent of all geometries in a layer.

Syntax

SDO_TUNE.EXTENT_OF (layername, min_X, max_X, min_Y, max_Y))

Keywords and Parameters

layername

 

Specifies the name of the data set layer. The layername is used to construct the name of the geometry and spatial index tables. Data type is VARCHAR2.

 

min_X

 

Minimum X value of the bounding rectangle. Data type is number.

 

max_X

 

Maximum X value of the bounding rectangle. Data type is number.

 

min_Y

 

Minimum Y value of the bounding rectangle. Data type is number.

 

max_Y

 

Maximum Y value of the bounding rectangle. Data type is number.

 

Returns

This procedure returns the coordinates of the minimum bounding rectangle for all geometric data in a layer. Data type is number for the four return values.

Usage Notes

None

Related Topics




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