PostGIS 緩沖區分析（查詢距離范圍內要素）

說明：

遇到個需求：需要查詢事發點周圍100米內的人和車，這個通過PostGIS的ST_DWithin函數很容易實現。
但是在實現過程中，遇到了三個不同的問題，在此總結一下。

解決方案：

方案一：

這種方式適用於PostGIS庫，在庫里直接寫SQL實現，入參直接可以用PostGIS的geometry格式。

--調用方式（參數：表名，坐標系id，表主鍵ID，緩沖區半徑，中心點）
select * from enc_buffer_bygeom('fm',3857,'gid',100,'0101000020110F0000F2D24D3662CA6841480C02EB46545241');

函數如下：

-- FUNCTION: public.func_buffer_bygeom(character varying, integer, character varying, double precision, character varying)
-- DROP FUNCTION public.func_buffer_bygeom(character varying, integer, character varying, double precision, character varying);
CREATE OR REPLACE FUNCTION public.func_buffer_bygeom(
	tb character varying,
	qsrid integer,
	qid character varying,
	qbuffer double precision,
	qgeom character varying)
    RETURNS TABLE(v_gid integer, v_res geometry, v_dis double precision) 
    LANGUAGE 'plpgsql'

    COST 100
    VOLATILE STRICT 
    ROWS 1000
    
AS $BODY$  

declare  
    v_gid integer; --主鍵
    v_res geometry; --要素
    v_dis double precision; --與目標距離
begin 
    RETURN QUERY EXECUTE 
    'select '||qId||',geom, ST_Distance(geom,'''||qGeom||''') from ' ||tb|| ' where ST_DWithin(geom,'''||qGeom||''','||qBuffer||')' ; 

end;  

$BODY$;

ALTER FUNCTION public.func_buffer_bygeom(character varying, integer, character varying, double precision, character varying)
    OWNER TO postgres;

方案二：

這種方式適用於PostGIS庫里的查詢（有geom字段的），就可以直接用此函數查詢。
相較於方案一的話，他更適合發布到geoserver中供前端調用，因為前端獲取WKT格式較方便。

--調用方式（參數：表名，坐標系id，表主鍵ID，緩沖區半徑，中心點）
select * from func_buffer('layer_grid',3857,'id',10,'POINT(12988813.522 4798555.074)');

函數如下：

-- FUNCTION: public.func_buffer(character varying, integer, character varying, double precision, character varying)
-- DROP FUNCTION public.func_buffer(character varying, integer, character varying, double precision, character varying);
CREATE OR REPLACE FUNCTION public.func_buffer(
	tb character varying,
	qsrid integer,
	qid character varying,
	qbuffer double precision,
	qgeom character varying)
    RETURNS TABLE(v_gid integer, v_res geometry, v_dis double precision) 
    LANGUAGE 'plpgsql'

    COST 100
    VOLATILE STRICT 
    ROWS 1000
    
AS $BODY$  

declare  
    v_gid integer; --主鍵
    v_res geometry; --要素
    v_dis double precision; --與目標距離
begin 
    RETURN QUERY EXECUTE 
    'select '||qId||',geom, ST_Distance(geom,ST_Geometryfromtext('''||qGeom||''','||qSrid||')) from ' ||tb|| ' where ST_DWithin(geom,ST_Geometryfromtext('''||qGeom||''','||qSrid||'),'||qBuffer||')' ; 

end;  

$BODY$;

ALTER FUNCTION public.func_buffer(character varying, integer, character varying, double precision, character varying)
    OWNER TO postgres;

方案三：

這種方式適用於對外部表做緩沖區分析（外部表只有x和y字段，沒有geom字段）
這種比較常見於業務庫和GIS空間數據庫分開的情況下（我們是mysql+postgis），業務庫只有存Xy字段，並不支持postgis的geometry類型
所以操作前需要通過外表關聯，將mysql表關聯到postgis，接着根據mysql中xy字段，構造geom字段
外表關聯方法參見：https://www.cnblogs.com/giser-s/p/11208818.html

--調用方式（參數：表名，坐標系id，表主鍵ID，緩沖區半徑，中心點）
select * from func_buffer_fetable('layer_grid',3857,'id','lng','lat',10,'POINT(12988813.522 4798555.074)');

函數如下：

-- FUNCTION: public.func_buffer_fetable(character varying, integer, character varying, character varying, character varying, double precision, character varying)
-- DROP FUNCTION public.func_buffer_fetable(character varying, integer, character varying, character varying, character varying, double precision, character varying);
CREATE OR REPLACE FUNCTION public.func_buffer_fetable(
	tb character varying,
	qsrid integer,
	qid character varying,
	qxfield character varying,
	qyfield character varying,
	qbuffer double precision,
	qgeom character varying)
    RETURNS TABLE(v_gid integer, v_res geometry, v_dis double precision) 
    LANGUAGE 'plpgsql'

    COST 100
    VOLATILE STRICT 
    ROWS 1000
    
AS $BODY$  

declare  
    v_gid integer; --主鍵
    v_res geometry; --要素
    v_dis double precision; --與目標距離
	v_record record;
begin 
RETURN QUERY EXECUTE  
	'select '||qId||',
	ST_Geometryfromtext(''POINT( ''||'|| qxfield ||'||'' ''||'|| qyfield ||'||'')'','||qSrid||'),
	ST_Distance(ST_Geometryfromtext(''POINT( ''||'|| qxfield ||'||'' ''||'|| qyfield ||'||'')'','||qSrid||'),ST_Geometryfromtext('''||qGeom||''','||qSrid||')) 
	from ' ||tb|| 
	' where ST_DWithin(ST_Geometryfromtext(''POINT( ''||'|| qxfield ||'||'' ''||'|| qyfield ||'||'')'','||qSrid||'),ST_Geometryfromtext('''||qGeom||''','||qSrid||'),'||qBuffer||')';
end;  

$BODY$;

ALTER FUNCTION public.func_buffer_fetable(character varying, integer, character varying, character varying, character varying, double precision, character varying)
    OWNER TO postgres;

方案四：

這種方式提前將PostGIS庫中geometry格式轉成了WKT格式（geomtext字段），方便直接查詢。
測試產物，不是很推薦這么做。

--調用方式（參數：表名，坐標系id，表主鍵ID，緩沖區半徑，中心點）
select * from func_buffer_bytxt('layer_grid',3857,'id',10,'POINT(12988813.522 4798555.074)');

函數如下：

-- FUNCTION: public.func_buffer_bytxt(character varying, integer, character varying, double precision, character varying)
-- DROP FUNCTION public.func_buffer_bytxt(character varying, integer, character varying, double precision, character varying);
CREATE OR REPLACE FUNCTION public.func_buffer_bytxt(
	tb character varying,
	qsrid integer,
	qid character varying,
	qbuffer double precision,
	qgeom character varying)
    RETURNS TABLE(v_gid integer, v_res geometry, v_dis double precision) 
    LANGUAGE 'plpgsql'

    COST 100
    VOLATILE STRICT 
    ROWS 1000
    
AS $BODY$  

declare  
    v_gid integer; --主鍵
    v_res geometry; --要素
    v_dis double precision; --與目標距離
begin 
    RETURN QUERY EXECUTE 
    'select '||qId||',geom, ST_Distance(st_geomfromtext(geomtext,'||qSrid||'),ST_Geometryfromtext('''||qGeom||''','||qSrid||')) from ' ||tb|| ' where ST_DWithin(geom,ST_Geometryfromtext('''||qGeom||''','||qSrid||'),'||qBuffer||')' ; 

end;  

$BODY$;

ALTER FUNCTION public.func_buffer_bytxt(character varying, integer, character varying, double precision, character varying)
    OWNER TO postgres;