create FUNCTION getdistance
(
i_latbegin REAL,i_lngbegin REAL,i_latend REAL,i_lngend REAL
)
RETURNS FLOAT
AS
$BODY$
--author :kenyon
--created :2012-06-12
--purpose :calc the distance between diff lat and lng
declare
v_distance real;
v_earth_radius real;
v_radlatbegin real;
v_radlatend real;
v_radlatdiff real;
v_radlngdiff real;
BEGIN
--地球半径
v_earth_radius:=6378.137;
v_radlatbegin := i_latbegin * pi()/180.0;
v_radlatend := i_latend * pi()/180.0;
v_radlatdiff := v_radlatbegin - v_radlatend;
v_radlngdiff := i_lngbegin * pi()/180.0 - i_lngend * pi()/180.0;
v_distance := 2 * asin(sqrt(power(sin(v_radlatdiff / 2),2) + cos(v_radlatbegin) * cos(v_radlatend) * power(sin(v_radlngdiff/2),2)));
v_distance := v_distance * v_earth_radius*1000;
RETURN v_distance;
END;
$BODY$
LANGUAGE 'plpgsql' VOLATILE; 目前只有这个应用用到计算空间距离，故暂时没去安装和应用postgis了。上述lng和lat分别是经度(longitude)和纬度(latitude)的简写。
参考的函数原型：
from math import sin,asin,cos,radians,fabs,sqrt
EARTH_RADIUS=6371 # 地球平均半径，6371km
def hav(theta):
s = sin(theta / 2)
return s * s
def get_distance_hav(lat0,lng0,lat1,lng1):
"用haversine公式计算球面两点间的距离。"
# 经纬度转换成弧度
lat0 = radians(lat0)
lat1 = radians(lat1)
lng0 = radians(lng0)
lng1 = radians(lng1)
dlng = fabs(lng0 - lng1)
dlat = fabs(lat0 - lat1)
h = hav(dlat) + cos(lat0) * cos(lat1) * hav(dlng)
distance = 2 * EARTH_RADIUS * asin(sqrt(h))
return distance