通過封裝常用的點、線段類型，並提供點、線間的相互關系運算，為計算幾何工具庫的編寫提供基礎框架。
代碼如下：（代碼正確性仍需測試，謹慎使用）
//參考 //www.2cto.com //www.2cto.com /* toolbox: Geometry algorithm toolbox author: alaclp email: [email protected] publish date: 2015-1-16 */ #include#include #include using namespace std; //預定義 #define Min(x, y) ((x) < (y) ? (x) : (y)) #define Max(x, y) ((x) > (y) ? (x) : (y)) //點對象 typedef struct Point { double x, y; //構造函數 Point(double x, double y) : x(x), y(y) {} //無參數時的構造函數 Point() : x(0), y(0) {} //取得到點pt的距離 double distance(const Point& pt) { return sqrt( (x - pt.x) * (x - pt.x) + (y - pt.y) * (y - pt.y)); } //判斷兩點是否同一個點 bool equal(const Point& pt) { return ((x - pt.x) == 0) && (y - pt.y == 0); } } Point; //線段對象 typedef struct PartLine { Point pa, pb; double length; PartLine() { length = 0; } //構造函數 PartLine(Point pa, Point pb) : pa(pa), pb(pb) { length = sqrt((pa.x - pb.x) * (pa.x - pb.x) + (pa.y - pb.y) * (pa.y - pb.y)); } void assign(const PartLine& pl) { pa = pl.pa; pb = pl.pb; length = pl.length; } //利用叉積計算點到線段的垂直距離 //注意：此結果距離有正負之分 //若pc點在線段的逆時針方向，則距離為正;否則，距離為副值 double getDistantToPoint(Point pc) { double area = crossProd(pc) / 2; return area * 2 / length; /* 利用海倫公式計算 PartLine pl1(this->pa, pc), pl2(this->pb, pc); double l1 = this->length, l2 = pl1.length, l3 = pl2.length; double s = (l1 + l2 + l3) / 2; //海倫公式 double area = sqrt(s * (s - l1) * (s - l2) * (s - l3)); return area * 2 / l1; */ } //向量的叉積 /* 計算向量的叉積（ABxAC A(x1,y1) B(x2,y2) C(x3,y3)）是計算行列式 | x1-x0 y1-y0 | | x2-x0 y2-y0 | 的結果(向量的叉積 AB X AC) */ //計算AB與AC的叉積---叉積的絕對值是兩向量所構成平行四邊形的面積 double crossProd(Point& pc) { //計算ab X ac return (pb.x - pa.x) * (pc.y - pa.y) - (pb.y - pa.y) * (pc.x - pa.x); } //判斷兩線段是否相交 bool isIntersected(PartLine& pl) { double d1, d2, d3, d4, d5, d6; d1 = pl.crossProd(pb); d2 = pl.crossProd(pa); d3 = crossProd(pl.pa); d4 = crossProd(pl.pb); d5 = crossProd(pl.pa); d6 = crossProd(pl.pb); //printf(%f %f %f %f %f %f , d1, d2, d3, d4, d5, d6); bool cond1 = d1 * d2 <= 0, //pb和pa在pl的兩側或線段或線段的延長線上 cond2 = d3 * d4 <= 0, //pl.pa和pl.pb在this的兩側或線段或線段的延長線上 cond3 = d5 != 0, //pl.pa不在線段和延長線上 cond4 = d6 != 0; //pl.pb不在線段和延長線上 return cond1 && cond2 && cond3 && cond4; } //判斷兩線段是否平行 bool isParallel(PartLine& pl) { double v1 = crossProd(pl.pa), v2 = crossProd(pl.pb); return (v1 == v2) && (v1 != 0); } //沿pa點旋轉theta PartLine rotateA(double theta) { float nx = pa.x +(pb.x - pa.x) * cos(theta) - (pb.y - pa.y) * sin(theta), ny = pa.y + (pb.x - pa.x) * sin(theta) + (pb.y - pa.y) * cos(theta); return PartLine(pa, Point(nx, ny)); } //沿pb點旋轉theta PartLine rotateB(double theta) { float nx = pb.x +(pa.x - pb.x) * cos(theta) - (pa.y - pb.y) * sin(theta), ny = pb.y + (pa.x - pb.x) * sin(theta) + (pa.y - pb.y) * cos(theta); return PartLine(Point(nx, ny), pb); } //判斷兩線段是否重疊或共線 bool inSameLine(PartLine& pl) { double v1 = crossProd(pl.pa), v2 = crossProd(pl.pb); if (v1 != v2) return false; if (v1 != 0) return false; return true; } //取得兩線段的相交點---如果不相交返回valid=false //如果多個交點，給出警告 Point getCrossPoint(PartLine& pl, bool& valid) { valid = false; if (!isIntersected(pl)) { //不相交 return Point(); } if ( inSameLine(pl) ) { //有交點且共線 if ( pa.equal(pl.pa) ) { valid = true; return pa; } if ( pa.equal(pl.pb) ) { valid = true; return pa; } if ( pb.equal(pl.pa) ) { valid = true; return pb; } if ( pb.equal(pl.pb) ) { valid = true; return pb; } //多個焦點 cout << 錯誤：計算交點結果數量為無窮 << endl; valid = false; return Point(); } //相交 Point pt1, pt2, pt3, result; pt1 = pa; pt2 = pb; pt3.x = (pt1.x + pt2.x) / 2; pt3.y = (pt1.y + pt2.y) / 2; double L1 = pl.crossProd(pt1), L2 = pl.crossProd(pt2), L3 = pl.crossProd(pt3); printf(%f %f %f=%f , L1, L2, L3, L1 + L2); while(fabs(L1) > 1e-7 || fabs(L2) > 1e-7) { valid = true; if (fabs(L1) < fabs(L2)) pt2 = pt3; else pt1 = pt3; pt3.x = (pt1.x + pt2.x) / 2; pt3.y = (pt1.y + pt2.y) / 2; result = pt3; L1 = pl.crossProd(pt1), L2 = pl.crossProd(pt2), L3 = pl.crossProd(pt3); printf(%f %f %f=%f , L1, L2, L3, L1 - L2); } return pt3; } //取得線段上離pt最近的點 Point getNearestPointToPoint(Point& pt) { Point pt1, pt2, pt3, result; pt1 = pa; pt2 = pb; pt3.x = (pt1.x + pt2.x) / 2; pt3.y = (pt1.y + pt2.y) / 2; double L1 = pt1.distance(pt), L2 = pt2.distance(pt), L3 = pt3.distance(pt); if (L1 == L2) return pt3; while(fabs(L1 - L2) > 1e-7) { if (L1 < L2) pt2 = pt3; else pt1 = pt3; pt3.x = (pt1.x + pt2.x) / 2; pt3.y = (pt1.y + pt2.y) / 2; result = pt3; L1 = pt1.distance(pt); L2 = pt2.distance(pt); L3 = pt3.distance(pt); //printf(%f %f %f=%f , L1, L2, L3, L1 - L2); } return result; } //取得一個點在線段上的鏡像點 Point getMirrorPoint(Point& pc) { } } PartLine; int main(void) { Point p1(0, 0), p2(1, 1), p3(0, 1.1), p4(0.5, 0.5+1e-10), p5(0.5, 0.5-1e-10), np; PartLine pl1(p1, p2), pl2(p3, p4), pl3(p3, p5); cout << pl1.getDistantToPoint(p3) << endl; cout << 線段1和2相交？ << pl1.isIntersected(pl2) << endl; np = pl1.getNearestPointToPoint(p5); cout << 最近點: << np.x << , << np.y << endl; bool isvalid; np = pl1.getCrossPoint(pl3, isvalid); cout << 兩線段的相交點： << (isvalid ? 有效:無效) << = << np.x << , << np.y << endl; PartLine plx = pl1.rotateA(M_PI / 2); printf(旋轉90度後：%f %f %f %f , plx.pa.x, plx.pa.y, plx.pb.x, plx.pb.y); return 0; }
