Postgis - 一个圆圈包含另一个圆圈

Question

我正在使用带有gps数据的postgis,并试图找出一个带有GPS坐标和半径(以米为单位)的圆圈是否包含另一个圆圈.

如果我不使用GPS坐标,但只是在图表上指向,我就能做到这一点,但如果我用lat和lon点代替,这就不行了:

-- A circle within a circle
SELECT ST_Contains(bigc,smallc) As bigcontainssmall
FROM (SELECT ST_Buffer(ST_MakePoint(21, 38)::geography, 40) As smallc,
         ST_Buffer(ST_MakePoint(21, 39)::geography, 400) AS bigc) foo;

思考？

Answer 1

我的方法是:

1. 通过SRID将CRS(坐标参考系统)分配给gps数据(我假设它们在WGS84中,因此是srid 4326)(ST_SetSRID(your_geom, 4326)这样做)
2. 然后(只有在你分配了srid 4326时才可以)将它们投射到地理位置(::geography这样做)以启用以米为单位设置缓冲区辐射线,
3. 然后将它们转换回几何体(::geometry这样做)以使st_contains功能起作用

查询:

    SELECT ST_Contains(bigc::geometry,smallc::geometry) as bigcontainssmall 
from (select 
st_buffer(ST_SetSRID(ST_MakePoint(-71.10434, 42.31506),4326)::geography,40) as smallc,
st_buffer(ST_SetSRID(ST_MakePoint(-71.10434, 42.31507),4326)::geography,400) as bigc) foo