SDO_GEOR_AGGR.mosaicSubset

9.6 SDO_GEOR_AGGR.mosaicSubset

Format

SDO_GEOR_AGGR.mosaicSubset(
     inGeoRasters     IN SYS_REFCURSOR, 
     pyramidLevel     IN NUMBER DEFAULT NULL, 
     outSRID          IN NUMBER DEFAULT NULL, 
     outModelCoordLoc IN NUMBER DEFAULT NULL, 
     referencePoint   IN SDO_GEOMETRY DEFAULT NULL, 
     cropArea         IN SDO_GEOMETRY DEFAULT NULL, 
     polygonClip      IN VARCHAR2 DEFAULT 'FALSE', 
     boundaryClip     IN VARCHAR2 DEFAULT 'TRUE', 
     layerNumbers     IN VARCHAR2 DEFAULT NULL, 
     outResolutions   IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     resolutionUnit   IN VARCHAR2 DEFAULT NULL, 
     mosaicParam      IN VARCHAR2 DEFAULT NULL, 
     storageParam     IN VARCHAR2 DEFAULT NULL, 
     outGeoRaster     IN OUT SDO_GEORASTER, 
     bgValues         IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     parallelParam    IN VARCHAR2 DEFAULT NULL);

SDO_GEOR_AGGR.mosaicSubset(
     georasterTableNames  IN VARCHAR2, 
     georasterColumnNames IN VARCHAR2, 
     pyramidLevel         IN NUMBER DEFAULT NULL, 
     outSRID             IN NUMBER DEFAULT NULL, 
     outModelCoordLoc    IN NUMBER DEFAULT NULL, 
     referencePoint      IN SDO_GEOMETRY DEFAULT NULL, 
     cropArea            IN SDO_GEOMETRY DEFAULT NULL, 
     polygonClip         IN VARCHAR2 DEFAULT 'FALSE', 
     boundaryClip        IN VARCHAR2 DEFAULT 'TRUE', 
     layerNumbers        IN VARCHAR2 DEFAULT NULL, 
     outResolutions      IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     resolutionUnit      IN VARCHAR2 DEFAULT NULL, 
     mosaicParam         IN VARCHAR2 DEFAULT NULL, 
     storageParam        IN VARCHAR2 DEFAULT NULL, 
     outGeoRaster        IN OUT SDO_GEORASTER, 
     bgValues            IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     parallelParam       IN VARCHAR2 DEFAULT NULL);

SDO_GEOR_AGGR.mosaicSubset(
     inGeoRasters     IN SYS_REFCURSOR, 
     pyramidLevel     IN NUMBER DEFAULT NULL, 
     elevationParam   IN VARCHAR2, 
     outSRID          IN NUMBER DEFAULT NULL, 
     outModelCoordLoc IN NUMBER DEFAULT NULL, 
     referencePoint   IN SDO_GEOMETRY DEFAULT NULL, 
     cropArea         IN SDO_GEOMETRY DEFAULT NULL, 
     polygonClip      IN VARCHAR2 DEFAULT 'FALSE', 
     boundaryClip     IN VARCHAR2 DEFAULT 'TRUE', 
     layerNumbers     IN VARCHAR2 DEFAULT NULL, 
     outResolutions   IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     resolutionUnit   IN VARCHAR2 DEFAULT NULL, 
     mosaicParam      IN VARCHAR2 DEFAULT NULL, 
     storageParam     IN VARCHAR2 DEFAULT NULL, 
     outGeoRaster     IN OUT SDO_GEORASTER, 
     bgValues         IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     parallelParam    IN VARCHAR2 DEFAULT NULL,
     referenceImage   IN SDO_GEORASTER DEFAULT NULL,
     referenceValue1  IN SDO_NUMBER_ARRAY DEFAULT NULL,
     referenceValue2  IN SDO_NUMBER_ARRAY DEFAULT NULL,
     refHistograms    IN SDO_GEOR_HISTOGRAM_ARRAY DEFAULT NULL);

SDO_GEOR_AGGR.mosaicSubset(
     georasterTableNames  IN VARCHAR2, 
     georasterColumnNames IN VARCHAR2, 
     pyramidLevel         IN NUMBER DEFAULT NULL, 
     elevationParam       IN VARCHAR2, 
     outSRID              IN NUMBER DEFAULT NULL, 
     outModelCoordLoc     IN NUMBER DEFAULT NULL, 
     referencePoint       IN SDO_GEOMETRY DEFAULT NULL, 
     cropArea             IN SDO_GEOMETRY DEFAULT NULL, 
     polygonClip          IN VARCHAR2 DEFAULT 'FALSE', 
     boundaryClip         IN VARCHAR2 DEFAULT 'TRUE', 
     layerNumbers         IN VARCHAR2 DEFAULT NULL, 
     outResolutions       IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     resolutionUnit       IN VARCHAR2 DEFAULT NULL, 
     mosaicParam          IN VARCHAR2 DEFAULT NULL, 
     storageParam         IN VARCHAR2 DEFAULT NULL, 
     outGeoRaster         IN OUT SDO_GEORASTER, 
     bgValues             IN SDO_NUMBER_ARRAY DEFAULT NULL, 
     parallelParam        IN VARCHAR2 DEFAULT NULL,
     referenceImage       IN SDO_GEORASTER DEFAULT NULL,
     referenceValue1      IN SDO_NUMBER_ARRAY DEFAULT NULL,
     referenceValue2      IN SDO_NUMBER_ARRAY DEFAULT NULL,
     refHistograms        IN SDO_GEOR_HISTOGRAM_ARRAY DEFAULT NULL);

Description

Performs advanced large-scale mosaicking or subsetting from a virtual mosaic or a collection of GeoRaster objects. The output data is written into a GeoRaster object for persistent storage or other processing. Internal rectification, common point rules, gap filling, and color balancing are performed whenever necessary.

Parameters

inGeoRasters

Source GeoRaster objects in a cursor.

georasterTableNames

Names (comma-separated) of the tables containing the source GeoRaster objects.

For information about defining and using MIN_X_RES$ and MAX_X_RES$ columns in these tables, see the Usage Notes and Improving Query Performance Using MIN_X_RES$ and MAX_X_RES$.

georasterColumnNames

Names (comma-separated) of the columns of type SDO_GEORASTER in tables corresponding to the table names in georasterTableNames.

pyramidLevel

Pyramid level of the source GeoRaster objects for the operation. This parameter is used when the outResolutions parameter is not specified; otherwise, the pyramid level of the source GeoRaster objects involved in the mosaic is determined by the outResolutions parameter.

The pyramidLevel parameter and the option pyramid=true in the storageParam parameter are valid only when the source GeoRaster objects have the same resolution on pyramid level 0.

If the outResolutions parameter is not null, the pyramidLevel parameter is ignored.

elevationParam

A string containing the elevation parameter average (average surface height). This parameter must be a quoted string that contains a keyword=value pair (for example, 'average=800'). This parameter specifies the elevation of the output GeoRaster object. If this parameter is null, 0 is assumed for average.

The use of the elevationParam parameter requires that the input GeoRaster objects have a 3D model SRID and a nonzero average surface height.

outSRID

Coordinate system for the output GeoRaster object. Must be either null or a value from the SRID column of the MDSYS.CS_SRS table.

outModelCoordLoc

A value specifying the model location of the base of the area represented by a cell: 0 for CENTER or 1 for UPPERLEFT. If null, CENTER is used.

referencePoint

A point of type SDO_GEOMETRY used as the reference point of mosaic. If a point is specified, the mosaicked image's upper left corner aligns with the reference point, that is, the distance between the referencePoint and the upper-left corner of the output will have an integer number of pixels. If this parameter is null, the reference point implicitly uses the upper-left corner of the cropArea, or when the cropArea is null, the upper-left corner of the output extent.

cropArea

Crop area definition. If the SDO_GEOMETRY object has a non-null SRID, the coordinates specified in the SDO_GEOMETRY object are in model space and the source GeoRaster objects must be georeferenced; otherwise, the coordinates specified in the SDO_GEOMETRY object are in cell space and the source GeoRaster objects can be georeferenced or non-georeferenced. If polygonClip is FALSE, the MBR of the cropArea is used to crop the mosaicked data. If polygonClip is TRUE, the geometry of the cropArea is used to crop the mosaicked data.

polygonClip

The string TRUE causes the cropArea value to be used to crop the mosaicked data; the string FALSE or a null value causes the MBR of the cropArea to be used to crop the mosaicked data.

boundaryClip

The string TRUE or a null value causes the boundary of the virtual mosaic to be used to clip the cropArea; the string FALSE causes the area that is outside the virtual mosaic but within the cropArea to be filled with the background value

layerNumbers

A string identifying the logical layer numbers on which the operation or operations are to be performed. Use commas to delimit the values, and a hyphen to indicate a range (for example, 2-4 for layers 2, 3, and 4). If not specified, the mosaic result contains the same number of bands as the source GeoRaster objects.

outResolutions

Resolution of the output GeoRaster data. If null, the default is the resolution of the first encountered GeoRaster object. See the Usage Notes for details.

resolutionUnit

The unit of the outResolutions parameter. If null, the default is the unit of the output SRID. If specified, it must be a quoted string in the format "unit=value" where value is the unit name value (a valid UNIT_OF_MEAS_NAME value from the SDO_UNITS_OF_MEASURE table). This parameter is ignored if outResolutions is null.

mosaicParam

A comma-separated quoted string of keyword=value pairs for specifying mosaic parameters. It can contain one or more of the keywords in Table 9-1.

Note:

For any numbers in string (VARCHAR2) parameters to GeoRaster subprograms, the period (.) must be used for any decimal points regardless of the locale.

Table 9-1 mosaicParam Keywords

Keyword	Explanation
cbreference	(Supported with the procedure formats that include the `referenceImage`, `referenceValue1`, /`referenceValue2`, and `refHistograms` parameters.) Specifies the source of the reference value used in `colorBalance`. Can have one of the following values: `VALUE`: The reference value is specified in the `referenceValue1` and `referenceValue2` parameters. `IMAGE`: The reference value is retrieved from the `referenceImage` parameter. `OVERLAP`: the reference value is derived from the overlapping area of the source images. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)
colorBalance	Specifies the method for color balancing. Can have one of the following values: `NONE` (the default): No color balancing is performed. `LINEARSTRETCHING`: Use the linear stretching method to stretch the source image’s cell values to the reference minimum and maximum value. If the `cbreference` parameter is `VALUE`, then parameter `referenceValue1` has the reference minimum values and parameter `referenceValue2` has the reference maximum values. If the `referenceValue1` or `referenceValue2` is null, default values 0 and 255 are used, respectively. If the `referenceValue1` or `referenceValue2` has only one value, it is applied to all the bands; otherwise, the reference values are corresponding to each band. Thus, the number of values in the SDO_NUMBER_ARRAY must be the same as the number of bands in the source images. If the `cbreference` parameter is `IMAGE`, then the minimum and maximum values of `referenceImage` are used as the reference. If the `cbreference` parameter is not specified, the `minVal` and `maxVal` parameters are used to specify the minimum and maximum reference values, respectively. `STATISTICMATCHING`: Stretch the source images to match the reference statistics. If the `cbreference` parameter is `VALUE`, then parameter `referenceValue1` has the reference mean value and parameter `referenceValue2` has the reference standard deviation value. If the `referenceValue1` or `referenceValue2` is null, default values 128 and 100 are used, respectively. If the `referenceValue1` or `referenceValue2` has only one value, it is applied to all the bands; otherwise, the reference values are corresponding to each band. Thus, the number of values in the SDO_NUMBER_ARRAY must be the same as the number of bands in the source images. If the `cbreference` parameter is `IMAGE`, then the reference image’s mean and standard deviation values are used for the matching. If the `cbreference` parameter is `OVERLAP`, then the mean and standard deviation values are derived from the overlapping area. If the `cbreference` parameter is not specified, the `std` and `mean` parameters are used to specify the reference statistics. `HISTOGRAMMATCHING`: Use the reference histogram as the source image’s histogram. If the `cbreference` parameter is `VALUE`, then parameter `referenceHistogram` defines the reference histograms for each band. If only one reference histogram is specified, it is applied to all the bands. If the `cbreference` parameter is `IMAGE`, then the referencce image’s histograms for each band are used as the reference for matching If the `cbreference` parameter is `OVERLAP`, then histograms at the overlapping area are used to derive the matching.
commonPointRule	Specifies the method for getting the cell value at the overlapping area. Can have one of the following values: `START`: The value from the first encountered GeoRaster object is used. `END`: The value from the last encountered GeoRaster object is used. `LATEST`: The value from the GeoRaster object that has the most recent `EndDateTime` in the metadata is used. `OLDEST`: The value from the GeoRaster object that has the oldest `EndDateTime` in the metadata is used. `CTC`: The call value from the GeoRaster object that is closest to the center of the output window is used. `HIGH`: The maximum cell value of all the overlapping GeoRaster objects is used. `LOW`: The minimum cell value of all the overlapping GeoRaster objects is used. `AVERAGE`: The average of all cell values from the overlapping GeoRaster objects is used. `HIGHRES`: The value from the GeoRaster object that has the highest spatial resolution is used.
fillGap	Specifies whether or not to fill the narrow gap between source images. `TRUE` causes any gap that is less than or equal to 2 pixels wide to be filled with the nearest-neighbor pixel value. `FALSE` causes any gaps to be filled with zero or `bgValue`.
maxVal	Ignored if `colorBalance` is not `LINEARSTRETCHING` or if the `cbreference` keyword is specified; otherwise, specifies the highest value in the range of the linear stretching method. Defaults to 255. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)
mean	Ignored if `colorBalance` is not `STATISTICMATCHING` or if the `cbreference` keyword is specified; otherwise, specifies the reference mean of the statistic matching method. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)
minVal	Ignored if `colorBalance` is not `LINEARSTRETCHING` or if the `cbreference` keyword is specified; otherwise, specifies the lowest value in the range of the linear stretching method. Defaults to 0. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)
nodata	Specifies whether or not to consider NODATA (NODATA value or NODATA bitmap mask) when handling the overlap area or when resampling is performed. The default value is `FALSE`. When handling the overlap area, `nodata=TRUE` causes any NODATA values cells not to be involved in the overlap area calculation; `nodata=FALSE` causes all the overlapped cells to be involved in the overlap area calculation. When resampling is performed and the resampling method is `BILINEAR`, `BIQUADRATIC`, `CUBIC`, `AVERAGE4`, or `AVERAGE16`, if any of the cells involved in the resampling has a NODATA value, then `nodata=TRUE` causes the result of the resampling to be a NODATA value.
resampling	Specifies the resampling method (if resampling is involved or rectification is needed) to be used during the mosaic operation. Can have one of the following values: `NN` (the default), `BILINEAR`, `BIQUADRATIC`, `CUBIC`, `AVERAGE4`, or `AVERAGE16`. For more information, see Resampling and Interpolation.
resamplingTolerance	Specifies the tolerance for not doing resampling when the source GeoRaster objects are not perfectly aligned. The value should be between 0 and 0.5, where the unit is pixel or cell (for example, `0.5` meaning one-half pixel or cell). If not specified, `0.5` is used, which means no resampling will occur.
resFilter	Specifies whether or not to filter the source GeoRaster objects to select only the GeoRaster object that is in the range of the output resolution (`outResolution` parameter). `TRUE` (the default) enables resolution filtering. `FALSE` disables resolution filtering, causing all the source GeoRaster objects to be involved in the mosaicking process. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)
std	Ignored if `colorBalance` is not `STATISTICMATCHING` or if the `cbreference` keyword is specified; otherwise, specifies the reference standard deviation for the statistic matching method. (Always ignored if specified in `appendParam` for SDO_GEOR_AGGR.append.)

storageParam

A string specifying storage parameters, as explained in Storage Parameters. If this parameter is null, the resulting GeoRaster object has the same storage parameters (blockSize, cellDepth, interleaving, and compression) as the first encountered source GeoRaster object in the model space (if applicable) or cell space. However, it is recommended that you specify the storage parameters, particularly the blocking size, as appropriate for the size of the output mosaic, unless you want the mosaic to have the same storage parameters as those of the first encountered GeoRaster object to be mosaicked.

If pyramid=true is specified, the pyramids of the source GeoRaster objects are mosaicked when the outResolutions parameter is null and the pyramidLevel parameter is not null. The maximum pyramid level of the result GeoRaster object is the minimal value of the maximum pyramid level of the source GeoRaster objects. By default, pyramid=false, and thus the pyramids are not mosaicked.

If bitmapmask=true is specified, the bitmap masks of the source GeoRaster objects are mosaicked also.

outGeoRaster

GeoRaster object to hold the result of the operation. Cannot be the same as any source GeoRaster object.

bgValues

Background cell values for filling partially empty raster blocks (full empty raster blocks are left as empty without filling). They are used to fill the empty areas resulted from the mosaicking operation, such as the areas that are outside of the clipping polygon or the gap areas not covered by any source images. (See alsoEmpty Raster Blocks.) The number of elements in the SDO_NUMBER_ARRAY object must be either one (same filling value used for all bands) or the band dimension size (a different filling value for each band, respectively). For example, SDO_NUMBER_ARRAY(1,5,10) fills the first band with 1, the second band with 5, and the third band with 10. The default bgValues are zero (0).

The filling values must be valid cell values as specified by the target cell depth.

parallelParam

Specifies the degree of parallelism for the operation. If specified, must be in the form parallel=n, where n is greater than 1. The database optimizer uses the degree of parallelism specified by this parameter. If not specified, then by default there is no parallel processing. (For more information, see Parallel Processing in GeoRaster.)

If parallelism is specified, the procedure performs an internal commit operation. If an error occurs (even if it is raised by the Oracle parallel server), you must delete the resulting mosaicked GeoRaster object explicitly in order to roll back the operation.

referenceImage

Specifies the reference image used during the color balance operation. If null, it defaults to the first image from the query.

referenceValue1

Specifies the reference value or values used during the color balance operation. The meaning of the values is determined by the color balance method.

referenceValue2

Specifies the reference value or values used during the color balance operation. The meaning of the values is determined by the color balance method.

referenceHistograms

Specifies the reference histograms used during the color balance operation.

Usage Notes

The first two formats of the procedure provide the basic color balancing method and assume that the elevation of the output GeoRaster object is 0. The last two formats of the procedure provide more advanced color balancing method using the reference values or reference images, and they let you specify the elevation value for the output GeoRaster object.

The source GeoRaster objects must be prepared images or raster data so that they can be mosaicked. That is, the GeoRaster objects to be mosaicked must:

Not be a mixture of georeferenced and nongeoreferenced objects. Either all of the objects are georeferenced, or none of the objects is georeferenced.
Have the same number of layers or bands. There is no restriction on the row and column dimension sizes of the source objects.

If the GeoRaster objects to be mosaicked are georeferenced, they are co-located according to their georeferencing information. If the GeoRaster objects are not georeferenced, they are co-located according to their ULTCoordinate values. (The ULTCoordinate is explained in GeoRaster Data Model.)

The resulting GeoRaster object's spatial reference metadata information is determined by the outSRID and outResolutions parameters. If outSRID is not specified, the SRID of the first encountered source GeoRaster object is used. If outResolutions is not specified, the spatial resolution of the first encountered source GeoRaster object at specified pyramid level (pyramidLevel parameter) is used. The spatial resolution must be set in the metadata of all the source images.

If any source GeoRaster object has a different SRID from outSRID or is not rectified, it is dynamically reprojected or rectified so that the mosaicked GeoRaster object has uniform SRID and spatial resolution values.

If the source GeoRaster objects overlap, data of the overlapping area follows the rules specified in the mosaicParam parameter. By default, the cell value of the last encountered source GeoRaster object is used.

The source GeoRaster objects that contributes to the output mosaic are selected by the cropArea parameter spatially and outResolutions parameter in resolution wise (resolution selection).

The cropArea parameter is used to query the source GeoRaster objects' spatial extents to determine the GeoRaster objects that are covered by the cropArea geometry,. Thus, a spatial index should be built on the spatialExtent attribute of the GeoRaster objects.
The outResolutions parameter is used to find the source GeoRaster objects so that the outResolutions value is within the resolution range of the source GeoRaster objects. A GeoRaster object's spatial resolution range is determined by the resolution at pyramid level 0 and the resolution at the top pyramid level of the GeoRaster object. It is a half pyramid lower than the pyramid level 0 and a half pyramid level higher than the top pyramid level. For example, if a GeoRaster object has a resolution of 30 meters at pyramid level 0 and a resolution of 960 meters at the top pyramid level 5, this GeoRaster object’s spatial resolution range is between 22.5 meters ((30 + 30/2)/2) and 1440 meters ((960 + 960*2)/2).

The resolution selection using the outResolutions parameter can be speeded up by defining the columns MIN_X_RES$ and MAX_X_RES$ (both of type NUMBER) in the tables listed in georasterTableNames parameter, where MIN_X_RES$ and MAX_X_RES$ specify the minimum and maximum spatial resolution values, respectively, of the source GeoRaster object. (A B-tree index should be created on the MIN_X_RES$ and MAX_X_RES$ columns if there are a large number of source GeoRaster objects.) To take advantage of this feature, the procedure format with the georasterTableNames parameter must be used. It also requires that the resolution values stored in the MIN_X_RES$ and MAX_X_RES$ columns have the same unit as the unit of the SRID that is stored in the source GeoRaster object spatialExtent attribute.

The resolution selection can be turned off by setting resFilter=false in the mosaicParam parameter. When the resolution selection is turned off, the source GeoRaster objects will only be filtered spatially.

If the source GeoRaster objects have empty raster blocks or do not cover the whole area, the mosaicked result GeoRaster object may have empty or partially empty raster blocks (see Empty Raster Blocks). A result raster block that is not covered by any of the source GeoRaster objects is kept empty. Any partially empty raster blocks are filled with the values specified in the bgValues parameter, or with 0 if the bgValues parameter is not specified.

If the bitmapmask parameter is set to true in the storageParam string, the bitmap masks are mosaicked. By default, the bitmap masks are not mosaciked. Note that the bitmap mask may also be considered as NODATA; and if they are, see the NODATA keyword in Table 9-1.

In order to use the colorBalance option in mosaicParam, you should you should call SDO_GEOR.generateStatistics on the source images to generate the image's statistics and store them in the metadata for the source image.

If all source GeoRaster objects are blank and have the same blankCellValue value, the resulting GeoRaster object is blank and has that blankCellValue value; otherwise, the resulting GeoRaster object is not blank.

The GeoRaster object to contain the results of the mosaic operation (georaster parameter) must not be any of the source GeoRaster objects (the objects on which the mosaic operation is performed).

The mosaic operation performs internal commit operations at regular intervals, and thus it cannot be rolled back. If the operation is interrupted, dangling raster blocks may exist in the raster data table. You can handle dangling raster blocks by maintaining GeoRaster objects and system data in the database, as explained as explained in Maintaining GeoRaster Objects and System Data in the Database.

For more information, see Large-Scale Image Mosaicking and Virtual Mosaic.

Examples

The following example shows how to mosaic the source images at the specified pyramidLevel. This requires that all the source images have the same spatial resolutions and have a pyramid generated on the specified pyramidLevel.

DECLARE
gr sdo_georaster;
BEGIN
    INSERT INTO georaster_table (georid, georaster)
        VALUES (10, SDO_GEOR.init('RDT_1',10))
        RETURNING georaster INTO gr;
    
-- mosaic at pyramidLevel=1,output SRID defaults to 
-- the SRID of the first source image, fillGap=true. 
-- Enable parallel processing with parallel degree set as 4.
    SDO_GEOR_AGGR.mosaicSubset('georaster_table_1, georaster_table_2', 
                   'georaster, georaster', 
                   1, null, null, null, null, null,
                   null, null, null, null, null, 
                   'fillGap=true', 
                   'blocking=optimalpadding, blocksize=(512,512,3)', 
                   gr, null, 'parallel=4');
 
    UPDATE georaster_table SET georaster = gr WHERE georid=10;
    COMMIT;                                                              
END;
/

The following example shows how to mosaic the first band of the source images with the outSRID, outResolutions and cropArea parameters. The overlapping area is determined by the commonPointRule mosaic parameter.

DECLARE
gr             sdo_georaster;
outSRID        number;
cropArea       sdo_geometry;
resolutions    sdo_number_array;
resolutionUnit varchar2(16);
bgValues       sdo_number_array;
layerNumbers   varchar2(8);
mosaicParam    varchar2(64);
BEGIN
    INSERT INTO georaster_table (georid, georaster)
        VALUES (10, SDO_GEOR.init('RDT_1',10))
        RETURNING georaster INTO gr;

    -- set the parameters
    outSRID := 4326;
    cropArea :=  sdo_geometry(2003, 26986, null,                 
              sdo_elem_info_array(1, 1003, 3), 
              sdo_ordinate_array(399180, 4247820, 
                                 496140,4353900) );
    resolutions := sdo_number_array(30, 30);
    resolutionUnit := ‘unit=meter’;
    layerNumbers := ‘0’;
    bgValues := sdo_number_array(0);
    mosaicParam := ‘commonPointRule=high, nodata=true’;

-- Enable parallel processing with parallel degree set as 4.
    SDO_GEOR_AGGR.mosaicSubset('georaster_table_1, georaster_table_2', 
                   'georaster, georaster', 
                   null, null, outSRID, null, null, cropArea,
                   null, null, layerNumbers, resolutions,
                   resolutionUnit, mosaicParam, 
                   'blocking=optimalpadding, blocksize=(512,512,3)', 
                   gr, bgValues, 'parallel=4');
 
    UPDATE georaster_table SET georaster = gr WHERE georid=10;
    commit;
END;
/

Parent topic: SDO_GEOR_AGGR Package Reference