基于PostGIS实现 MultiPolygon与Polygon的洞去除和MultiPolygon合并为Polygon

熟悉GIS开发的小伙伴，都知道Polygon和MultiPolygon是可以有洞的，MultiPolygon内的Polygon有可能是不相邻的。在做一些三方方平台对接时，可能出现不支持带洞的Polygon或者MultiPolygon。今天这里分享一下，如何基于PostGIS实现

1. 如何去除Polygon和MultiPolygon图形内的洞
2. 如何将MultiPolygon保留轮廓转为Polygon

去除洞

使用下面代码，可以去除Polygon内的洞

select ST_BuildArea(st_exteriorring(geom))

• 去除前
• 去除后
  去除Polygon和MultiPolygon图形内的洞 脚本

CREATE OR REPLACE FUNCTION "public"."polygon_remove_hole"("m_polygon" geometry)
    RETURNS geometry AS
$BODY$
DECLARE
    --去除多边形内的洞
    polygon_type text;
    temp         _geometry;
    temp_polygon geometry;
BEGIN
    polygon_type := GeometryType(m_polygon);
    raise notice '类型-%', polygon_type;
--简单

    if polygon_type = 'MULTIPOLYGON' then
        raise notice '类型-%', polygon_type;
        temp := array []::_geometry;
        for temp_polygon in (select geom from ST_Dump(m_polygon))
            loop
                if ST_NumInteriorRings(temp_polygon) > 0 then
                    raise notice '类型-有洞%',GeometryType(temp_polygon);
                    temp := array_append(temp, ST_BuildArea(ST_ExteriorRing(temp_polygon)));
                else
                    raise notice '类型-无洞';
                    temp := array_append(temp, temp_polygon);
                end if;

            end loop;
        return ST_Union(temp);
    ELSEIF polygon_type = 'GEOMETRYCOLLECTION' then
        raise notice '类型-%', polygon_type;
        temp := array []::_geometry;
        for temp_polygon in (select geom from ST_Dump(m_polygon))
            loop
                if ST_NumInteriorRings(temp_polygon) > 0 then
                    temp := array_append(temp, ST_BuildArea(ST_ExteriorRing(temp_polygon)));
                else
                    temp := array_append(temp, temp_polygon);
                end if;

            end loop;
        return ST_Union(temp);
    ELSEIF polygon_type = 'POLYGON' then
        raise notice '类型-%', polygon_type;
        --有内环的，去除内外
        if ST_NumInteriorRings(m_polygon) > 0 then
            return ST_BuildArea(st_exteriorring(m_polygon));
        end if;
    end IF;
    return m_polygon;
END ;
$BODY$
    LANGUAGE plpgsql VOLATILE
                     COST 100

将MultiPolygon基于凹包的方式转为Polygon

基于下面函数可以实现，如果有洞

ST_ConcaveHull(m_polygon,0.1,false);

• 合并前



• 合并后

合并并去除多边形内洞脚本

CREATE OR REPLACE FUNCTION "public"."merge_polygon"("m_polygon" geometry)
    RETURNS geometry AS
$BODY$
DECLARE
    -- 提取多边形外轮廓
    polygon_type text;


BEGIN
    polygon_type := GeometryType(m_polygon);
    raise notice '类型-%', polygon_type;
--简单

    if polygon_type = 'MULTIPOLYGON' then
        raise notice '类型-%', polygon_type;
        m_polygon:=polygon_remove_hole(m_polygon);
        return ST_ConcaveHull(m_polygon,0.1,false);
    ELSEIF polygon_type = 'GEOMETRYCOLLECTION' then
        raise notice '类型-%', polygon_type;
    ELSEIF polygon_type = 'POLYGON' then
        raise notice '类型-%', polygon_type;
        --有内环的，去除内外
        if ST_NumInteriorRings(m_polygon)>0 then
            return polygon_remove_hole(m_polygon);
        end if;
    end IF;
    return m_polygon;
END ;
$BODY$
    LANGUAGE plpgsql VOLATILE
                     COST 100