ST_MapAlgebraFct
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名称

ST_MapAlgebraFct — 2 波段版本 - 通过在提供的 2 个输入栅格波段和像素类型上应用有效的 PostgreSQL 函数来创建新的单波段栅格。 如果未指定波段，则假定为波段 1。 如果未指定，范围类型默认为 INTERSECTION。

大纲

raster ST_MapAlgebraFct(raster rast1, raster rast2, regprocedure tworastuserfunc, text pixeltype=same_as_rast1, text extenttype=INTERSECTION, text[] VARIADIC userargs);

raster ST_MapAlgebraFct(raster rast1, integer band1, raster rast2, integer band2, regprocedure tworastuserfunc, text pixeltype=same_as_rast1, text extenttype=INTERSECTION, text[] VARIADIC userargs);

Description

[警告]

ST_MapAlgebraFct 自 2.1.0 起已弃用。 使用ST_MapAlgebra (callback function version)（回调函数版本）代替。

创建一个新的单波段栅格，该栅格是通过对输入栅格 rast1、rast2 应用由tworastuserfunc 指定的有效 PostgreSQL 函数而形成的。 如果未指定 band1 或 band2，则假定为 band 1。 新栅格将具有与原始栅格相同的地理参考、宽度和高度，但只有一个波段。

如果传入pixeltype，则新栅格将具有该像素类型的波段。 如果将像素类型传递为 NULL 或省略，则新的栅格波段将具有与输入 rast1 波段相同的像素类型。

Tworastuserfunc 参数必须是 SQL 或 PL/pgSQL 函数的名称和签名，转换为 regprocedure。 PL/pgSQL 函数示例如下：

Code
CREATE OR REPLACE FUNCTION simple_function_for_two_rasters(pixel1 FLOAT, pixel2 FLOAT, pos INTEGER[], VARIADIC args TEXT[])
RETURNS FLOAT
AS $$ BEGIN
    RETURN 0.0;
END; $$
LANGUAGE 'plpgsql' IMMUTABLE;

Tworastuserfunc 可以接受三个或四个参数：一个双精度值、一个双精度值、一个可选的整数数组和一个可变文本数组。 第一个参数是 rast1 中单个栅格像元的值（无论栅格数据类型如何）。 第二个参数是 rast2 中的单个栅格像元值。 第三个参数是当前处理单元的位置，格式为“{x,y}”。 第四个参数指示ST_MapAlgebraFct 的所有剩余参数均应传递给tworastuserfunc。

将 regprodedure 参数传递给 SQL 函数需要传递完整的函数签名，然后转换为 regprocedure 类型。 要将上述示例 PL/pgSQL 函数作为参数传递，参数的 SQL 为：

Code
'simple_function(double precision, double precision, integer[], text[])'::regprocedure

请注意，参数包含函数名称、函数参数类型、名称和参数类型周围的引号以及对 regprocedure 的强制转换。

Tworastuserfunc 的第四个参数是可变文本数组。 任何 ST_MapAlgebraFct 调用的所有尾随文本参数都会传递到指定的tworastuserfunc，并包含在 userargs 参数中。

[注意]

有关 VARIADIC 关键字的更多信息，请参阅 PostgreSQL 文档和查询语言 (SQL) 函数的“具有可变参数数量的 SQL 函数”部分。
[注意]

无论您是否选择将任何参数传递给用户函数进行处理，text[] 参数在tworastuserfunc都是必需的。

可用性: 2.0.0

示例：将栅格作为单独的波段覆盖在画布上

The deprecated two-raster callback form can often be expressed with the modern two-raster ST_MapAlgebra (callback function version) expression variant. This build-time example renders two input rasters and their averaged overlap.

Code
WITH canvas AS (
    SELECT ST_AddBand(
        ST_MakeEmptyRaster(80, 80, 0, 80, 1, -1, 0, 0, 0),
        1, '8BUI', 0, 0
    ) AS rast
), inputs AS (
    SELECT
        ST_AsRaster(ST_Buffer(ST_Point(30, 40), 25), rast, '8BUI', 80, 0)
            AS raster_1,
        ST_AsRaster(ST_Buffer(ST_Point(50, 40), 25), rast, '8BUI', 220, 0)
            AS raster_2
    FROM canvas
), variants AS (
    SELECT 'raster 1' AS title, raster_1 AS rendered FROM inputs
    UNION ALL
    SELECT 'raster 2', raster_2 FROM inputs
    UNION ALL
    SELECT 'averaged', ST_MapAlgebra(
        raster_1, 1,
        raster_2, 1,
        '([rast1] + [rast2]) / 2',
        '8BUI',
        'UNION'
    ) FROM inputs
)
SELECT title, ST_AsPNG(rendered) AS image
FROM variants
ORDER BY title DESC;
栅格输出
title   | image
----------+-------------------------
 raster 2 | PNG image, 50 x 50 pixels
 raster 1 | PNG image, 50 x 50 pixels
 averaged | PNG image, 70 x 50 pixels
Figure
Geometry figure for visual-rt-st-mapalgebrafct2-01

Define our user defined function.

Code

CREATE OR REPLACE FUNCTION raster_mapalgebra_union(
    rast1 double precision,
    rast2 double precision,
    pos integer[],
    VARIADIC userargs text[]
)
    RETURNS double precision
    AS $$
    DECLARE
    BEGIN
        CASE
            WHEN rast1 IS NOT NULL AND rast2 IS NOT NULL THEN
                RETURN ((rast1 + rast2)/2.);
            WHEN rast1 IS NULL AND rast2 IS NULL THEN
                RETURN NULL;
            WHEN rast1 IS NULL THEN
                RETURN rast2;
            ELSE
                RETURN rast1;
        END CASE;

        RETURN NULL;
    END;
    $$ LANGUAGE 'plpgsql' IMMUTABLE COST 1000;

Prepare a test table of rasters.

Code
DROP TABLE IF EXISTS map_shapes;
CREATE TABLE map_shapes(rid serial PRIMARY KEY, rast raster, bnum integer, descrip text);
INSERT INTO map_shapes(rast,bnum, descrip)
WITH mygeoms
    AS ( SELECT 2 As bnum, ST_Buffer(ST_Point(90,90),30) As geom, 'circle' As descrip
            UNION ALL
            SELECT 3 AS bnum,
                ST_Buffer(ST_GeomFromText('LINESTRING(50 50,150 150,150 50)'), 15) As geom, 'big road' As descrip
            UNION ALL
            SELECT 1 As bnum,
                ST_Translate(ST_Buffer(ST_GeomFromText('LINESTRING(60 50,150 150,150 50)'), 8,'join=bevel'), 10,-6) As geom, 'small road' As descrip
            ),
   -- define our canvas to be 1 to 1 pixel to geometry
   canvas
    AS ( SELECT ST_AddBand(
        ST_MakeEmptyRaster(
            250,
            250,
            ST_XMin(e)::integer,
            ST_YMax(e)::integer,
            1, -1, 0, 0),
        '8BUI'::text,
        0) As rast
        FROM (SELECT ST_Extent(geom) As e,
                    Max(ST_SRID(geom)) As srid
                    from mygeoms
                    ) As foo
            )
-- return our rasters aligned with our canvas
SELECT ST_AsRaster(m.geom, canvas.rast, '8BUI', 240) As rast, bnum, descrip
                FROM mygeoms AS m CROSS JOIN canvas
UNION ALL
SELECT canvas.rast, 4, 'canvas'
FROM canvas;

Map algebra on single-band rasters and then collect the result with ST_AddBand.

Code
INSERT INTO map_shapes(rast,bnum,descrip)
SELECT ST_AddBand(ST_AddBand(rasts[1], rasts[2]),rasts[3]), 4, 'map bands overlay fct union (canvas)'
    FROM (SELECT ARRAY(SELECT ST_MapAlgebraFct(
            m1.rast,
            m2.rast,
            'raster_mapalgebra_union(double precision, double precision, integer[], text[])'::regprocedure,
            '8BUI',
            'FIRST')
                FROM map_shapes As m1 CROSS JOIN map_shapes As m2
    WHERE m1.descrip = 'canvas' AND m2.descrip <
> 'canvas' ORDER BY m2.bnum) As rasts) As foo;

A compact, executable callback example. The source rasters and their averaged overlap are rendered at build time.

Code
CREATE OR REPLACE FUNCTION pg_temp.raster_average(
    value_1 double precision,
    value_2 double precision,
    position integer[],
    VARIADIC userargs text[]
) RETURNS double precision
LANGUAGE SQL IMMUTABLE
AS 'SELECT COALESCE(($1 + $2) / 2.0, $1, $2)';

WITH canvas AS (
    SELECT ST_AddBand(
        ST_MakeEmptyRaster(80, 80, 0, 80, 1, -1, 0, 0, 0),
        1, '8BUI', 0, 0
    ) AS rast
), inputs AS (
    SELECT
        ST_AsRaster(ST_Buffer(ST_Point(30, 40), 25), rast, '8BUI', 80, 0)
            AS raster_1,
        ST_AsRaster(ST_Buffer(ST_Point(50, 40), 25), rast, '8BUI', 220, 0)
            AS raster_2
    FROM canvas
), variants AS (
    SELECT 'raster 1' AS title, raster_1 AS rendered FROM inputs
    UNION ALL
    SELECT 'raster 2', raster_2 FROM inputs
    UNION ALL
    SELECT 'averaged', ST_MapAlgebraFct(
        raster_1,
        raster_2,
        'pg_temp.raster_average(double precision,double precision,integer[],text[])'::regprocedure,
        '8BUI',
        'UNION'
    ) FROM inputs
)
SELECT title, ST_AsPNG(rendered) AS image
FROM variants
ORDER BY title DESC;
栅格输出
title    | image
----------+---------------------------
 raster 2 | PNG image, 50 x 50 pixels
 raster 1 | PNG image, 50 x 50 pixels
 averaged | PNG image, 70 x 50 pixels

需要额外参数的用户定义函数

Code
CREATE OR REPLACE FUNCTION raster_mapalgebra_userargs(
    rast1 double precision,
    rast2 double precision,
    pos integer[],
    VARIADIC userargs text[]
)
    RETURNS double precision
    AS $$
    DECLARE
    BEGIN
        CASE
            WHEN rast1 IS NOT NULL AND rast2 IS NOT NULL THEN
                RETURN least(userargs[1]::integer,(rast1 + rast2)/2.);
            WHEN rast1 IS NULL AND rast2 IS NULL THEN
                RETURN userargs[2]::integer;
            WHEN rast1 IS NULL THEN
                RETURN greatest(rast2, random()*userargs[3]::integer)::integer;
            ELSE
                RETURN greatest(rast1, random()*userargs[4]::integer)::integer;
        END CASE;

        RETURN NULL;
    END;
    $$ LANGUAGE 'plpgsql' VOLATILE COST 1000;

SELECT ST_MapAlgebraFct(
    m1.rast,
    1,
    m1.rast,
    3,
    'raster_mapalgebra_userargs(double precision, double precision, integer[], text[])'::regprocedure,
    '8BUI',
    'INTERSECT',
    '100', '200', '200', '0')
                FROM map_shapes As m1
    WHERE m1.descrip = 'map bands overlay fct union (canvas)';

The generated callback figure above demonstrates the raster alignment and overlap used by this variant; the exact callback result remains available as text.