├── README.md
└── 基于网格的点抽稀算法


/README.md:
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1 | # point_dilution
2 | 利用plpgsql写的基于postgis的点抽稀算法，目前没有将表名单独封装出来，可以建函数之前手动改一下 *select * from tycd_view* ，只是提供一个思路大家参考
3 | 


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/基于网格的点抽稀算法:
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 1 | --drop FUNCTION point_simplify_grid;
 2 | CREATE OR REPLACE FUNCTION point_simplify_grid(
 3 |         PAR_minx                         double precision,
 4 | 		PAR_miny                         double precision,
 5 | 		PAR_maxx                         double precision,
 6 | 		PAR_maxy                         double precision, 
 7 |         PAR_threshold                    double precision
 8 | ) RETURNS geometry AS $$
 9 | DECLARE
10 |         REC_points         			RECORD;
11 |         ARR_result_points  			geometry[];
12 |         GEO_point          			geometry;
13 |         grid_key            		VARCHAR(10);
14 |         GEOM_result        			geometry;
15 |         grid_num_x              INTEGER;
16 |         grid_num_y              INTEGER;
17 |         grid_json               jsonb;
18 | BEGIN
19 | 		grid_num_x := ceil((PAR_maxx - PAR_minx)/PAR_threshold);
20 | 		grid_num_y := ceil((PAR_maxy - PAR_miny)/PAR_threshold);
21 | 		grid_json :='{}'::jsonb;
22 |         ARR_result_points :='{}'::geometry[];
23 | 		for REC_points in select * from tycd_view where geom && st_makeenvelope(PAR_minx,PAR_miny,PAR_maxx,PAR_maxy,4326) LOOP
24 | 			grid_key := ceil((st_x(REC_points.geom)-PAR_minx)/PAR_threshold)||','||ceil((st_y(REC_points.geom)-PAR_miny)/PAR_threshold);
25 | 			if  NOT(grid_json?grid_key)  THEN
26 | 				ARR_result_points := array_append(ARR_result_points, st_setsrid(REC_points.geom,4326));
27 | 				grid_json :=grid_json||('{"'||grid_key||'":true}')::jsonb;
28 | 			end if;
29 | 		end loop;
30 | 	    GEOM_result := st_union(ARR_result_points);
31 |         return GEOM_result;
32 | END;
33 | $$ LANGUAGE plpgsql;
34 | --select st_asgeojson(point_simplify_grid(73,3,135,53,0.2))
35 | 


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