調用ST_CurvatureRadius計算軌跡每個中間點的轉動半徑 - ApsaraDB RDS

計算軌跡每個中間點的轉動半徑，返回一個浮點數組。

文法

double precision[] ST_CurvatureRadius(trajectory traj, boolean hasdirection default false);

參數

參數名稱

描述

traj

軌跡對象。

hasdirection

是否計算軌跡的轉向方向。

如果為true，則向逆時針方向轉向時，返回負值。

描述

對軌跡的每個中間點（假設某個軌跡有n個點，則其有n-2個中間點），計算軌跡在此點的轉動半徑。如果在此點沿直線運動，或停留在原地，則轉動半徑為無窮。轉動半徑越小說明轉彎越急。

樣本

SELECT ST_CurvatureRadius(ST_MakeTrajectory('STPOINT'::leaftype,'LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8)', '2000-01-01', '2000-01-01'::timestamp+ '1 day'::interval* (ST_NPoints('LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8)')-1), '{}'));
  st_curvatureradius   
-----------------------
 {5,Infinity,Infinity}


SELECT ST_CurvatureRadius(ST_MakeTrajectory('STPOINT'::leaftype,'LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0)', '2000-01-01', '2000-01-01'::timestamp+ '1 day'::interval* (ST_NPoints('LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0)')-1), '{}'));
st_curvatureradius 
-----------
 {5,Infinity,Infinity,Infinity,Infinity,5}


SELECT ST_CurvatureRadius(ST_MakeTrajectory('STPOINT'::leaftype,'LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0)', '2000-01-01', '2000-01-01'::timestamp+ '1 day'::interval* (ST_NPoints('LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0)')-1), '{}'), true);
 st_curvatureradius 
-----------
 {5,Infinity,Infinity,Infinity,Infinity,-5}


SELECT ST_CurvatureRadius(ST_MakeTrajectory('STPOINT'::leaftype,'LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0, 0 4, 3 4)', '2000-01-01', '2000-01-01'::timestamp+ '1 day'::interval* (ST_NPoints('LINESTRING(0 0, 0 8, 6 8, 12 8, 12 8, 6 8, 0 8, 0 0, 0 4, 3 4)')-1), '{}'), true);
st_curvatureradius
-----------
 {5,Infinity,Infinity,Infinity,Infinity,-5,0,2.5}