ST_Reclassify-ApsaraDB RDS(RDS)-阿里云帮助中心

Syntax

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

Parameters

Parameter	Description
`raster_obj`	The raster object to reclassify.
`reclassexpr`	A JSON array that defines the reclassification rules for each band.
`storageOption`	A JSON string that controls how the output raster is stored.

reclassexpr

reclassexpr is a JSON array. Each element configures one band.

Parameter	Type	Default	Description
`band`	integer	—	Band index, starting from 0.
`remap`	object	—	Maps input pixel value ranges to output values. See remap syntax.
`nodata`	boolean	`false`	`true`: pixels with nodata values produce nodata output. `false`: nodata pixels are treated as regular numeric values.
`nodataValue`	float8	`0`	The nodata value assigned in the output.

remap syntax

Each key-value pair in remap maps an input range to an output value or range.

Interval notation

Symbol	Meaning	Example
`[`	Greater than or equal to (≥)	`[100` → value ≥ 100
`(`	Greater than (>)	`(100` → value > 100
`]`	Less than or equal to (≤)	`100]` → value ≤ 100
`)`	Less than (<)	`100)` → value < 100

The default interval is (] (open on the left, closed on the right).

Complete interval examples

Expression	Equivalent condition
`[a,b]`	a ≤ value ≤ b
`(a,b]`	a < value ≤ b
`[a,b)`	a ≤ value < b
`(a,b)`	a < value < b

Mapping methods

Three mapping methods are available. All use comma-separated values to define input ranges and output values.

Method	Input values	Output values	Example
Range-to-value	n+1 values (n intervals)	n values	`"(300,400,500]":"80,90"`
Range-to-range	n values	n values	`"300,400,500":"80,90,100"` and `"[300,400,500]":"80,90,100"`
Value-to-value	1 value	1 value	`"10":"1"`

Rules:

Pixel values outside all mapped ranges are treated as nodata.
Ranges must not overlap (the same pixel value cannot belong to two ranges).

reclassexpr examples

Example 1: Single band, range-to-value mapping

Reclassify band 0:

0 < value ≤ 100 → 20
100 < value ≤ 200 → 50
All other values → nodata

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

Example 2: Single band, multiple disjoint ranges

Multiple segmented values are supported. Pixel values beyond the range are set to nodata values.

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

Example 3: Two bands with nodata control

Band 0 uses nodata: true—pixels with nodata values produce nodata output, and out-of-range pixels get a nodata value of 999. Band 1 uses nodata: false—nodata pixels are calculated as regular values, and out-of-range pixels get a nodata value of 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
  }
]

For band 1, the range-to-range mapping "(400,600,800]":"20,90,130" maps values within each interval:

400 < value ≤ 600 → interpolated between 20 and 90
600 < value ≤ 800 → interpolated between 90 and 130

storageOption

Parameter	Type	Default	Description
`chunking`	boolean	Same as input	Whether to store the output as chunks.
`chunkdim`	string	Same as input	Chunk dimensions. Takes effect only when `chunking` is `true`.
`chunktable`	string	`''`	Name of the chunk table. An empty string generates a temporary chunk table with a random name, valid for the current session only. Specify a name to retain the output across sessions.
`compression`	string	Same as input	Compression algorithm. Valid values: `none`, `jpeg`, `zlib`, `png`, `lzo`, `lz4`.
`quality`	integer	Same as input	Compression quality. Applies only to the `jpeg` algorithm.
`interleaving`	string	Same as input	Interleaving method: `bip` (band interleaved by pixel, BIP), `bil` (band interleaved by line, BIL), or `bsq` (band sequential, BSQ).
`endian`	string	Same as input	Byte order: `NDR` (little endian) or `XDR` (big endian).
`celltype`	string	Same as input	Pixel type of the output raster.

Examples

The following examples reclassify band 0 of a raster using the interval (0,100,200] → 20,50.

Store results in a temporary table (current session only)

-- Create the temporary table
CREATE TEMP TABLE rast_reclassify_result_temp(id integer, rast raster);

-- Run reclassification and store the result
INSERT INTO rast_reclassify_result_temp(id, rast)
SELECT 1, ST_Reclassify(rast, '[{"band":0,"remap":{"(0,100,200]":"20,50"}}]')
FROM reclass_table;

Store results in a permanent table

-- Create the permanent table
CREATE TABLE rast_reclassify_result(id integer, rast raster);

-- Run reclassification and store the result
INSERT INTO rast_reclassify_result(id, rast)
SELECT 1, ST_Reclassify(rast, '[{"band":0,"remap":{"(0,100,200]":"20,50"}}]')
FROM reclass_table;

The chunktable parameter in storageOption defaults to an empty string, which creates a temporary chunk table valid only for the current session. To retain the reclassified raster across sessions, specify a chunktable name.