AbelVM · November 3, 2023 16:09 · dramael · Feb 19, 2019 · amangeruca · Jan 21, 2022
diff --git a/README.md b/README.md
diff --git a/LICENSE b/LICENSE
 The MIT License (MIT)

 Copyright (c) 2018 Abel Vázquez Montoro

 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.

 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
diff --git a/st_kdensity.sql b/st_kdensity.sql
 CREATE OR REPLACE FUNCTION ST_KDensity(
    ids bigint[],
    geoms geometry[]
 )
 RETURNS TABLE(
    id bigint,
    geom geometry,
    kdensity integer
 )
 AS $$
 DECLARE
    mc geometry;
    c integer;
    k numeric;
 BEGIN

    mc := ST_Centroid(ST_Collect(geoms));
    c := array_length(ids, 1);
    k := sqrt(1/ln(2));

    RETURN QUERY
    WITH
    dist as (
        SELECT
            t.gid,
            t.g,
            ST_Distance(t.g, mc) as distance
        FROM
            unnest(ids, geoms) as t(gid, g)
    ),
    md as (
        SELECT
            percentile_cont(0.5) WITHIN GROUP (ORDER BY distance) as median
        FROM 
            dist
    ),
    sd as (
        -- https://pro.arcgis.com/en/pro-app/tool-reference/spatial-statistics/standard-distance.htm
        SELECT
            sqrt(
                (
                    sum((ST_X(g)-ST_X(mc))^2) +
                    sum((ST_Y(g)-ST_Y(mc))^2)
                )/ c
            ) as standard_distance
        FROM 
            dist
    ),
    sr as (
        SELECT
            0.9 * least(
                sd.standard_distance, 
                k * md.median
            ) * c^(-0.2) as search_radius
        FROM 
            sd, md
    )
    SELECT
        gid as id,
        g as geom, 
        kd::int as kdensity
    FROM
        sr,
        dist as a,
        LATERAL(
            SELECT
                count(*) as kd
            FROM dist _b
            WHERE ST_DWithin(a.g, _b.g, sr.search_radius)
        ) b;
 END;
 $$
 LANGUAGE plpgsql  IMMUTABLE PARALLEL SAFE;
	The MIT License (MIT)

	Copyright (c) 2018 Abel Vázquez Montoro

	Permission is hereby granted, free of charge, to any person obtaining a copy
	of this software and associated documentation files (the "Software"), to deal
	in the Software without restriction, including without limitation the rights
	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the Software is
	furnished to do so, subject to the following conditions:

	The above copyright notice and this permission notice shall be included in all
	copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	SOFTWARE.
	CREATE OR REPLACE FUNCTION ST_KDensity(
	ids bigint[],
	geoms geometry[]
	)
	RETURNS TABLE(
	id bigint,
	geom geometry,
	kdensity integer
	)
	AS $$
	DECLARE
	mc geometry;
	c integer;
	k numeric;
	BEGIN

	mc := ST_Centroid(ST_Collect(geoms));
	c := array_length(ids, 1);
	k := sqrt(1/ln(2));

	RETURN QUERY
	WITH
	dist as (
	SELECT
	t.gid,
	t.g,
	ST_Distance(t.g, mc) as distance
	FROM
	unnest(ids, geoms) as t(gid, g)
	),
	md as (
	SELECT
	percentile_cont(0.5) WITHIN GROUP (ORDER BY distance) as median
	FROM
	dist
	),
	sd as (
	-- https://pro.arcgis.com/en/pro-app/tool-reference/spatial-statistics/standard-distance.htm
	SELECT
	sqrt(
	(
	sum((ST_X(g)-ST_X(mc))^2) +
	sum((ST_Y(g)-ST_Y(mc))^2)
	)/ c
	) as standard_distance
	FROM
	dist
	),
	sr as (
	SELECT
	0.9 * least(
	sd.standard_distance,
	k * md.median
	) * c^(-0.2) as search_radius
	FROM
	sd, md
	)
	SELECT
	gid as id,
	g as geom,
	kd::int as kdensity
	FROM
	sr,
	dist as a,
	LATERAL(
	SELECT
	count(*) as kd
	FROM dist _b
	WHERE ST_DWithin(a.g, _b.g, sr.search_radius)
	) b;
	END;
	$$
	LANGUAGE plpgsql IMMUTABLE PARALLEL SAFE;