最小二乘拟合

本文对最小二乘拟合直线中出现的问题，当直线垂直时参数无法求出，使用ax+by+c=0或者p=xcos(a)+ysin(a)计算量会增加，针对这种情况，本算做了修正可以判断直线垂直情况。

//最小二乘法直线拟合ay = kx + b
static int _rtCalculateLine(const RtPoint* src, const int num, float* k, float* b, int* a)
{
    if (NULL == src || num < 2 ) return -1;

    int i = 0;
    long x = 0, y = 0, xx = 0, xy = 0, yy = 0, tem = 0;

    while(i < num)
    {
        x += (src + i)->x;
        y += (src + i)->y;
        xx += (src + i)->x * (src + i)->x;
        xy += (src + i)->x * (src + i)->y;
        yy += (src + i)->y * (src + i)->y;
        i++;
    }

    tem = xx*num - x*x;
    if(0 == tem)
    {
        tem = yy*num - y*y;
        if( 0 == tem) return -1;

        *k = (num*xy - x*y)/tem;
        *b = -(x - (*k)*y)/num;
        *a = 0;
        return 0;
    }

    *k = (num*xy - x*y)/tem;
    *b = (y - (*k)*x)/num;
    *a = 1;

    return 0;
}