Algebraic and analytical operation function ST_Reclassify-ApsaraDB RDS(RDS)-阿里云帮助中心

The ST_Reclassify function returns a raster object. The resulting object has the same spatial reference and resolution as the original raster. The number of bands is specified by the reclassexpr parameter.

Syntax

raster ST_Reclassify(raster raster_obj,
        cstring reclassexpr default NULL
         cstring storageOption default '')

Parameters

Parameter Name	Description
raster_obj	The raster object to reclassify.
reclassexpr	A JSON string that specifies the numerical intervals for classification.
storageOption	A JSON string that specifies the storage options for the result.

The reclassexpr parameter is an array of JSON objects. Each object specifies the operation parameters for a band. The parameters are as follows.

Parameter Name	Description	Type	Default value	Notes
band	The band number.	integer	None	The band number. The value starts from 0.
remap	The parameters used for classification.	object	-	-
nodata	Specifies whether to use nodata.	boolean	false	If set to true, pixels with nodata values are classified as nodata. If false, the value is treated as a numeric value.
nodataValue	The nodata value.	float8	0	The new nodata value.

The remap parameter specifies how to map original pixel values to new pixel values.

The key represents the original pixel value range. It consists of one or more numerical values separated by commas. You can specify open or closed boundaries for the range.
- (Indicates a value greater than)
- A right parenthesis `)` means less than.
- A right bracket `]` means less than or equal to.
- A left bracket `[` means greater than or equal to.
The default is (].
The value represents the new pixel value that results from the mapping. It consists of one or more numerical values separated by commas.
Three mapping methods are available:
- Range-to-range: The number of values that define the original pixel range is the same as the number of values that define the new pixel range. For example, "300,400,500":"80,90,100" and "[300,400,500]":"80,90,100".
- Range-to-value: The original pixel range is defined by one more value than the new pixel range. For example, "(300,400,500]":"80,90".
- Value-to-value: The original and new pixel ranges are each defined by a single value. For example, "10":"1".
Pixel values that do not fall into any specified mapping range are set to the nodata value.
A pixel value cannot be included in multiple ranges.

Examples

Example 1

The following example shows a reclassification operation on band 0:

if 0<old_value<=100
    new_value = 20
else if100<old_value<=200
    new_value = 50
else
    new_value = 0

[ 
   { 
      "band":0,
      "remap":{ 
            "(0,100,200]":"20,50"
      }
   }
]

Example 2

You can specify multiple value segments. Pixel values outside the specified ranges are set to the nodata value.

[ 
   { 
      "band":0,
      "remap":{ 
            "(0,100,200]":"20,50",
            "(300,400,500]":"80,90,100"
      }
   }
]

Example 3

The following example demonstrates a reclassification operation on band 0:

if 0<old_value<=100
    new_value = 20
else if100<old_value<=200
    new_value = 50
else
    new_value = 999

and a reclassification operation on band 1:

if 400<old_value<=600
    new_value = 20+(old_value-400)/200 * (90-20)
else if600<old_value<=800
    new_value = 90+(old_value-600)/200 * (130-90)
else
    new_value = 0

[ 
   { 
      "band":0,
      "remap":{
         "(0,100,200]":"20,50"
      },
      "nodata":true,
      "nodataValue":999
   },
   { 
      "band":1,
      "remap":{
        "(400,600,800]":"20,90,130"
      },
      "nodata":false,
      "nodataValue":0
   }
]

The storageOption parameters are as follows.

Parameter Name	Description	Type	Default value	Notes
chunking	Specifies whether to use chunk-based storage.	boolean	Same as the original raster	-
chunkdim	The dimension information of the chunk.	string	Same as the original raster	This parameter takes effect only when chunking is set to true.
chunktable	The name of the chunk table.	string	''	If an empty string ('') is passed, a temporary chunk table with a random name is created to store the data. This temporary table is valid only for the current session. To maintain an accessible clipped object, specify a chunk table name.
compression	The type of compression algorithm.	string	Same as the original raster	The supported algorithms are none, jpeg, zlib, png, lzo, and lz4.
quality	The compression quality.	integer	Same as the original raster	This parameter applies only to the JPEG compression algorithm.
interleaving	The interleaving method.	string	Same as the original raster	Must be one of the following: bip: Band interleaved by pixel BIL: Band Interleaved by Pixel bsq: Band Sequential
endian	The byte order.	string	Same as the original raster	Must be one of the following: NDR: Little endian XDR: Big endian
celltype	The pixel type.	string	Same as the original raster	-

Example

-- A permanent table
CREATE TABLE rast_reclassify_result(id integer, rast raster);
-- A temporary table
CREATE TEMP TABLE rast_reclassify_result_temp(id integer, rast raster);

-- Store the result in the temporary table
INSERT INTO rast_reclassify_result_temp(id, rast) 
select 1, ST_Reclassify(rast, '[{"band":0,"remap":{"(0,100,200]":"20,50"}}]') 
from reclass_table