5.4 Mathematical Operations

A major use of raster algebra is to apply mathematical models to raster layers from different sources.

To apply mathematical operations on one or multiple layers, which could be from one or more GeoRaster objects, to generate a new GeoRaster object, you can use the SDO_GEOR_RA.rasterMathOp procedure.

For most formats of this procedure, the operation parameter specifies an array of arithmeticExpr strings used to calculate raster cell values in the output GeoRaster object. Each element of the array corresponds to a layer in the output GeoRaster object.

Note that booleanExpr can be also used as arithmeticExpr, as is done in Example 5-8.

Example 5-9 Mathematical Operations (1)

Example 5-9 calls the SDO_GEOR_RA.rasterMathOp procedure to generate a new 6-layer GeoRaster object from a 3-layer source GeoRaster object, and follows these rules to calculate cell values of the target GeoRaster object:

• The cell value of the first three layers of target GeoRaster object is equal to the value of the corresponding layer of source GeoRaster object, minus 10.

• The cell value of the last three layers of target GeoRaster object is equal to the value of the first three layers of the source GeoRaster object, respectively.

DECLARE
  geor   SDO_GEORASTER;
  geor1  SDO_GEORASTER;
  geor2  SDO_GEORASTER;
BEGIN
  SELECT georaster INTO geor FROM georaster_table WHERE georid = 1;
  INSERT into georaster_table values (16, sdo_geor.init('rdt_1', 16)) returning georaster into geor1;
  sdo_geor_ra.rasterMathOp(geor,SDO_STRING2_ARRAY('{0,0}-10','{0,1}-10','{0,2}-10','{0,0}','{0,1}','{0,2}'),null,geor1);
  UPDATE georaster_table SET georaster = geor1 WHERE georid = 16;
  COMMIT;
END;
/
 
PL/SQL procedure successfully completed.
 
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'') FROM georaster_table WHERE georid=1;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(181, 163, 159)
 
1 row selected.
 
--  In the results of the next SELECT statement, note:
--  171=181-10
--  153=163-10
--  149=159-10
--  181=181
--  163=163
--  159=159
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'') FROM georaster_table WHERE georid =16;
SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(171, 153, 149, 181, 163, 159)
 
1 row selected.

Example 5-10 Mathematical Operations (2)

Example 5-10 applies an operation on a 2-element GeoRaster array (containing two 3-layer source GeoRaster objects) to generate a new 3-layer GeoRaster object.

DECLARE
  geor       SDO_GEORASTER;
  geor1      SDO_GEORASTER;
  geor2      SDO_GEORASTER;
  geo_array  SDO_GEORASTER_ARRAY;
BEGIN
  SELECT georaster INTO geor FROM georaster_table WHERE georid = 1;
  SELECT georaster INTO geor2 FROM georaster_table WHERE georid = 2;
  INSERT into georaster_table values (17, sdo_geor.init('rdt_1', 17)) returning georaster into geor1;
  geo_array:=SDO_GEORASTER_ARRAY(geor,geor2);
  sdo_geor_ra.rasterMathOp(geo_array,SDO_STRING2_ARRAY('{0,0}-0.5*{1,0}','{0,1}-0.5*{1,1}','{0,2}-0.5*{1,2}'),null,geor1,'false',null,'parallel=4');
  UPDATE georaster_table SET georaster = geor1 WHERE georid = 17;
  COMMIT;
END;
/
 
PL/SQL procedure successfully completed.
 
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'') FROM georaster_table WHERE georid=1 or georid=2;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(181, 163, 159)
SDO_NUMBER_ARRAY(60, 80, 90)
 
2 rows selected.
 
-- In the results of the next SELECT statement, note:
-- 151=181-0.5*60
-- 123=163-0.5*80
-- 114=159-0.5*90
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'') FROM georaster_table WHERE georid =17;

SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(151, 123 114)
 
1 row selected.

Example 5-11 Mathematical Operations (3)

Example 5-11 applies a subtraction operation on two 3-layer input GeoRaster objects to generate a new GeoRaster object. The example also includes several calls to the SDO_GEOR.getCellValue function to show "before" and "after" values.

SELECT sdo_geor.getcellvalue(georaster,0,10,10,'0-2') FROM georaster_table WHERE georid=1 OR georid=5 ORDER BY georid;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,10,10,'0-2')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(88, 137, 32)
SDO_NUMBER_ARRAY(98, 147, 42)
 
2 rows selected.
 
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'0-2') FROM georaster_table WHERE georid=1 OR georid=5 ORDER BY georid;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'0-2')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(181, 163, 159)
SDO_NUMBER_ARRAY(191, 173, 169)
 
2 rows selected.
 
DECLARE
  geor0  SDO_GEORASTER;
  geor   SDO_GEORASTER;
  geor1  SDO_GEORASTER;
BEGIN
  SELECT georaster INTO geor FROM georaster_table WHERE georid = 1;
  SELECT georaster INTO geor0 FROM georaster_table WHERE georid = 5;
  INSERT into georaster_table values (6, sdo_geor.init('rdt_1', 6)) returning georaster into geor1;
  sdo_geor_ra.rasterMathOp(geor0,geor,null,sdo_geor_ra.OPERATOR_SUBTRACT,null,geor1);
  UPDATE georaster_table SET georaster = geor1 WHERE georid = 6;
  COMMIT;
END;
/
 
PL/SQL procedure successfully completed.
 
SELECT sdo_geor.getcellvalue(georaster,0,10,10,'0-2') FROM georaster_table WHERE georid=6;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,10,10,'0-2')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(10, 10, 10)
 
1 row selected.
 
SELECT sdo_geor.getcellvalue(georaster,0,100,100,'0-2') FROM georaster_table WHERE georid=6;
 
SDO_GEOR.GETCELLVALUE(GEORASTER,0,100,100,'0-2')
--------------------------------------------------------------------------------
SDO_NUMBER_ARRAY(10, 10, 10)
 
1 row selected.