KML 文件始终为 lat/long 并使用 SRID=4326。如果您使用geography
. 地理是在纬度/经度数据上混合 4 公里公制度量的好方法……太好了,你试过了!
试试这个语句来修复强制转换,并使用参数化点构造函数:
SELECT ST_Buffer(ST_MakePoint(21.304116745663165, 38.68607570952619)::geography, 4000);
如果您需要将其转换回几何体,::geometry
请在末尾添加一个转换。
更新准确性
上一个答案在内部将几何图形(通常)重新投影到该点适合的 UTM 区域(参见ST_Buffer)。如果该点位于两个 UTM 边界的边缘,这可能会导致轻微的失真。大多数人不会关心这些错误的大小,但通常会是几米。但是,如果您需要亚毫米精度,请考虑构建动态方位角等距投影。这需要 PostGIS 2.3 ST_Transform
,并且改编自另一个答案:
CREATE OR REPLACE FUNCTION geodesic_buffer(geom geometry, dist double precision,
num_seg_quarter_circle integer)
RETURNS geometry AS $$
SELECT ST_Transform(
ST_Buffer(ST_Point(0, 0), $2, $3),
('+proj=aeqd +x_0=0 +y_0=0 +lat_0='
|| ST_Y(ST_Centroid($1))::text || ' +lon_0=' || ST_X(ST_Centroid($1))::text),
ST_SRID($1))
$$ LANGUAGE sql IMMUTABLE STRICT COST 100;
CREATE OR REPLACE FUNCTION geodesic_buffer(geom geometry, dist double precision)
RETURNS geometry AS 'SELECT geodesic_buffer($1, $2, 8)'
LANGUAGE sql IMMUTABLE STRICT COST 100;
-- Optional warppers for geography type
CREATE OR REPLACE FUNCTION geodesic_buffer(geog geography, dist double precision)
RETURNS geography AS 'SELECT geodesic_buffer($1::geometry, $2)::geography'
LANGUAGE sql IMMUTABLE STRICT COST 100;
CREATE OR REPLACE FUNCTION geodesic_buffer(geog geography, dist double precision,
num_seg_quarter_circle integer)
RETURNS geography AS 'SELECT geodesic_buffer($1::geometry, $2, $3)::geography'
LANGUAGE sql IMMUTABLE STRICT COST 100;
运行其中一个功能的简单示例是:
SELECT geodesic_buffer(ST_MakePoint(21.304116745663165, 38.68607570952619)::geography, 4000);
为了比较到每个缓冲点的距离,这里是每个测地线的长度(旋转椭圆体上的最短路径,即 WGS84)。首先这个函数:
SELECT count(*), min(buff_dist), avg(buff_dist), max(buff_dist)
FROM (
SELECT ST_Distance((ST_DumpPoints(geodesic_buffer(poi, dist)::geometry)).geom, poi) AS buff_dist
FROM (SELECT ST_MakePoint(21.304116745663165, 38.68607570952619)::geography AS poi, 4000 AS dist) AS f
) AS f;
count | min | avg | max
-------+----------------+-----------------+----------------
33 | 3999.999999953 | 3999.9999999743 | 4000.000000001
将此与 ST_Buffer (答案的第一部分)进行比较,这表明它偏离了大约 1.56 m:
SELECT count(*), min(buff_dist), avg(buff_dist), max(buff_dist)
FROM (
SELECT ST_Distance((ST_DumpPoints(ST_Buffer(poi, dist)::geometry)).geom, poi) AS buff_dist
FROM (SELECT ST_MakePoint(21.304116745663165, 38.68607570952619)::geography AS poi, 4000 AS dist) AS f
) AS f;
count | min | avg | max
-------+----------------+------------------+----------------
33 | 4001.560675049 | 4001.56585986067 | 4001.571105793