ApsaraDB RDS:ST_AsHMT

Syntaxe

bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, int4 value default 1, boolean point_mode default false);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, int4 value);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, int4 value, boolean point_mode);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, float8 value);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, float8 value, boolean point_mode);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, int4 value, cstring config);
bytea ST_AsHMT(geometry geometry_set, geometry extent, int4 width, int4 height, float8 value, cstring config);

Valeur renvoyée

Renvoie une structure de données binaire basée sur Protocol Buffers (Protobuf) représentant la valeur agrégée pour chaque cellule de la grille. Le schéma est le suivant :

syntax = "proto2";
option optimize_for = LITE_RUNTIME;

message HMT {
    required Type type = 1; // data value type
    required uint32 rows = 2;   // rows of matrix
    required uint32 columns = 3; // columns of matrix
    required uint32 srid = 4; // spatial reference identifier
    required float  xmin = 5; // xmin
    required float  ymin = 6; // ymin
    required float  xmax = 7; // xmax
    required float  ymax = 8; // ymax

    oneof matrix {
        intMatrix intValues = 10;
        doubleMatrix doubleValues = 11;
    }

    message intMatrix {
        repeated sint32 values = 12 [packed = true];
    }

    message doubleMatrix {
        repeated double values = 13 [packed = true];
    }

    enum Type {
        INT32 = 0;
        DOUBLE = 1;
    }
}

Paramètres

Description

Cette fonction convertit un ensemble d'objets géométriques en une tuile de carte thermique (HMT) selon une étendue géographique et une résolution spécifiées.

La fonction transforme automatiquement les géométries d'entrée pour qu'elles correspondent à la référence spatiale du paramètre extent si elles diffèrent.

Le paramètre config est une chaîne JSON qui spécifie la méthode de calcul. Le tableau suivant décrit les options disponibles.

Exemples

-- The following examples use a sample table named test_table, which is created with this statement.
CREATE TABLE test_table AS
SELECT i num,
    ST_SetSrid(st_makepoint((i-0.5)::numeric, (i-0.5)::numeric), 4326) geom,
    i*100::int4 weight,
    i*i*i::float8 volume
FROM generate_series(1, 10) i;

-- Count the number of geometries in each grid cell.
-- This is the simplest use case and does not require a `value` parameter.
SELECT ST_AsHMT(geom, -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    1024,        -- Width, in pixels
    800        -- height
)
FROM test_table;

---------
\x080010a0061880083284...

-- Sum the values in the `weight` column for each grid cell.
SELECT ST_AsHMT(geom, -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    1024,        -- Width
    800,       -- height
    weight     -- value column
)
FROM test_table;
---------
\x080010a0061880...

-- Sum the result of a computed expression for each grid cell.
-- The function returns a DOUBLE type matrix because the expression returns a float8 value.
SELECT ST_AsHMT(geom, -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    1024,        -- Width
    800,        -- height
    weight / volume * 1.2     -- complex value
)
FROM test_table;
---------
\x080110a0061880083a85...

-- Use point mode to count only geometries whose centers are in a grid cell.
SELECT ST_AsHMT(geom, -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    1024,        -- Width, in pixels
    800,        -- height
    1::integer,  -- value
    true        -- point mode
)
FROM test_table;
---------
\x080010a0061880083...

-- Filter the input data before aggregation by using a WHERE clause.
SELECT ST_AsHMT(geom, -- geometry column
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    1024,        -- Width, in pixels
    800        -- height
)
FROM test_table
WHERE num <5;
---------
\x080010a00618...

-- Calculate the average weight by using the `config` parameter.
SELECT ST_AsHMT(geom,
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    256,        -- Width, in pixels
    256,        -- height
    weight, 
    '{"type":"avg"}'::cstring)
FROM test_table;
---------
\x080010a00618...

-- Find the minimum weight in point mode by using the `config` parameter.
SELECT ST_AsHMT(geom,
    ST_MakeEnvelope(0, 0, 10, 10, 4326), -- Extent
    256,        -- Width, in pixels
    256,        -- height
    weight, 
    '{"type":"min", "point_mod":true}'::cstring)
FROM test_table;
---------
\x080010a00618...