SQL/POSTGIS 使用函数实现ST_Intersects

来源：互联网发布：奥飞娱乐怎么样知乎编辑：程序博客网时间：2024/04/28 10:54

create or replace function ST_LineIntersects(x1 float, y1 float, x2 float, y2 float, x3 float, y3 float, x4 float, y4 float)     returns booleanas $$declare a1 float;        a2 float;        b1 float;        b2 float;        c1 float;        c2 float;begin    a1 = y2 - y1;    b1 = x1 - x2;    c1 = a1*x1 + b1*y1;    a2 = y4 - y3;    b2 = x3 - x4;    c2 = a2*x3 + b2*y3;    if (a1*x3 + b1*y3) = c1 and (a1*x4 + b1*y4) = c1 then    begin        if (min(x1,x2)<=min(x3,x4) and min(x3,x4)<=max(x1,x2)) or (min(x1,x2)>=min(x3,x4) and max(x3,x4)>=min(x1,x2)) then             return true;        else             return false;        end if;    end;    elsif ((a1*x3+b1*y3-c1)*(a1*x4+b1*y4-c1)<=0) and ((a2*x1+b2*y1-c2)*(a2*x2+b2*y2-c2)<=0) then    return true;    end if;    return false;end;$$ language plpgsql;

算法思路，相交线段必然是一条线段的两点分在另一条线段的两侧，则另L1的两端点在L2的两侧，L2的两端点在L1的两侧，则相交成立。

0 0