地理信息系统算法题—

1、已知一线段 AB，在某个方向选择一点 P，输入距离 d，求线段 AB 延长距离 d 后的点坐标； protected PointF GetAppendDist(PointF temp,List pts) { PointF temppt; PointF pt = temp; PointF fpt = new PointF(pts[0].X, pts[0].Y); PointF lpt = new PointF(pts[1].X, pts[1].Y); Vector3D Linevec = new Vector3D(lines[1].X - lines[0].X, lines[1].Y - lines[0].Y, 0); double Len = Linevec.Length; Vector3D linepa = new Vector3D(pt.X - fpt.X, pt.Y - fpt.Y, 0); double pa = linepa.Length; Vector3D linepb = new Vector3D(pt.X - lpt.X, pt.Y - lpt.Y, 0); double pb = linepb.Length; double distance = Convert.ToDouble(this.appenddist.Text.ToString()); float xd, yd; if (pa > pb) { xd = lpt.X + ((lpt.X - fpt.X) * (float)distance) / (float)Len; yd = lpt.Y + ((lpt.Y - fpt.Y) * (float)distance) / (float)Len; temppt = new PointF(xd, yd); } else { xd = fpt.X + ((fpt.X - lpt.X) * (float)distance) / (float)Len; yd = fpt.Y + ((fpt.Y - lpt.Y) * (float)distance) / (float)Len; temppt = new PointF(xd, yd); } return temppt; } 2、判断两线段是否相交； public float maxvalue(float p1,float p2) { float p=0; if (p1 >= p2) { p = p1; } else p = p2; return p; } public float minvalue(float p1, float p2) { float p = 0;

if (p1 <= p2) { p = p1; } else p = p2; return p; } protected void isLineInterset(List lines) { float maxPx = maxvalue(lines[0].X, lines[1].X);//线段 p 中最大 X 坐标 float maxQx = maxvalue(lines[2].X, lines[3].X); //线段 q 中最大 X 坐标 float maxPy = maxvalue(lines[0].Y, lines[1].Y);//线段 p 中最大 Y 坐标 float maxQy = maxvalue(lines[2].Y, lines[3].Y);//线段 q 中最大 Y 坐标 float minPx = minvalue(lines[0].X, lines[1].X);//线段 p 中最小 X 坐标 float minQx = minvalue(lines[2].X, lines[3].X);//线段 q 中最小 X 坐标 float minPy = minvalue(lines[0].Y, lines[1].Y);//线段 p 中最小 Y 坐标 float minQy = minvalue(lines[2].Y, lines[3].Y);//线段 q 中最小 Y 坐标 if (maxPx <= minQx || maxQx <= minPx || maxPy <= minQy || maxQy <= minPy) { MessageBox.Show("两线段不相交..."); return; } else { Vector3D VecP1 = new Vector3D(lines[0].X, lines[0].Y, 0); Vector3D VecP2 = new Vector3D(lines[1].X, lines[1].Y, 0); Vector3D VecQ1 = new Vector3D(lines[2].X, lines[2].Y, 0); Vector3D VecQ2 = new Vector3D(lines[3].X, lines[3].Y, 0); Vector3D CrossProduct1 = Vector3D.CrossProduct((VecP1 - VecQ1), (VecQ2 - VecQ1)); Vector3D CrossProduct2 = Vector3D.CrossProduct((VecQ2 - VecQ1), (VecP2 - VecQ1)); Vector3D CrossProduct3 = Vector3D.CrossProduct((VecQ1 - VecP1), (VecP2 - VecQ1)); Vector3D CrossProduct4 = Vector3D.CrossProduct((VecP2 - VecP1), (VecQ2 - VecP1)); if (Vector3D.DotProduct(CrossProduct1, CrossProduct2) >= 0 &&

Vector3D.DotProduct(CrossProduct3, CrossProduct4) >= 0) { MessageBox.Show("两直线相交"); } else MessageBox.Show("两直线不相交！"); } } 3、多边形重心计算； int n=poly .Count ; float[] PolyCentroid; float[] Xpoints = new float[n]; float[] Ypoints = new float[n]; for (int i = 0; i <= poly.Count - 1;i++ ) { Xpoints[i] = poly[i].X; Ypoints[i] = poly[i].Y; } PolyCentroid = polyCentroid(Xpoints,Ypoints, n); protected float[] polyCentroid(float[] x, float[] y, int n) { float[] Centroid = null; float XCentroid, YCentroid, area; int i, j; float ai, atmp = 0, xtmp = 0, ytmp = 0; for (i = n - 1, j = 0; j < n;i=j,j++ ) { ai = x[i] * y[j] - x[j] * y[i]; atmp += ai; xtmp += (x[j] + x[i]) * ai; ytmp += (y[j] + y[i]) * ai; } area = atmp / 2; if (atmp!=0) { XCentroid = xtmp / (3 * atmp); YCentroid = ytmp / (3 * atmp); } else { return null; } Centroid = new float[] { XCentroid, YCentroid }; return Centroid; } 4、编程实现八方向矢量线栅格化； protected void RasterLineByCenter(PointF fpt,PointF lpt)//八方向栅格化 {

PointF p1 = fpt; PointF p2 = lpt; PointF Center=new PointF(); int Size=10; int k = (int)(lines[0].Y / 10); int m = (int)(lines[0].X / 10); int k1 = (int)(lines[1].Y / 10); int m1 = (int)(lines[1].X / 10); if (Math.Abs(lines[1].Y - lines[0].Y) >= Math.Abs(lines[1].X - lines[0].X))//行数大于列数 { if ((p2.Y - p1.Y) != 0) { int tempRow, tempRow1; if (k < k1) { tempRow = k; tempRow1 = k1; } else { tempRow = k1; tempRow1 = k; } float pk = (p2.X - p1.X) / (p2.Y - p1.Y); for (int Row = tempRow; Row <= tempRow1; Row++) { float CenterY = ((Row + 1) * Size + Row * Size) / 2; float CenterX = (CenterY - p1.Y) * pk + p1.X; Center = new PointF(CenterX, CenterY); int i = (int)CenterY / 10; int j = (int)CenterX / 10; RasterationLine(db[i, j]); ptsnew.Add(new PointF(i+1, j+1)); } } else //水平线栅格化 { if (m > m1) //首点在右，尾点在左 { for (int clo = m1 + 1; clo <= m; clo++) { RasterationLine(db[k, clo]); ptsnew.Add(new PointF(k+1, clo+1)); } }

else //首点在左，尾点在右 { for (int clo = m + 1; clo <= m1; clo++) { RasterationLine(db[k, clo]); ptsnew.Add(new PointF(k+1, clo+1)); } } } } else //列数大于行数的情况 { if ((p2.X - p1.X) != 0) { int tempCol, tempCol1; if (m < m1) { tempCol = m; tempCol1 = m1; } else { tempCol = m1; tempCol1 = m; } float pk=(p2.Y-p1.Y)/(p2.X-p1.X); for (int Col = tempCol; Col <= tempCol1; Col++) { float CenterX = ((Col + 1) * Size+Col*Size) / 2; float CenterY = (CenterX - p1.X) * pk + p1.Y; Center = new PointF(CenterX, CenterY); int i = (int)CenterY / 10; int j = (int)CenterX / 10; RasterationLine(db[i, j]); ptsnew.Add(new PointF(i+1, j+1)); } } else //垂直线栅格化 { if (k > k1) //首点在下，尾点在上 { for (int row = k1; row <= k; row++) { RasterationLine(db[row, m]);

ptsnew.Add(new PointF(row+1, m+1)); } } else //首点在上，尾点在下 { for (int row = k; row <= k1; row++) { RasterationLine(db[row, m]); ptsnew.Add(new PointF(row+1, m+1)); } } } } } 5、编程实现全路径矢量线栅格化； protected void RasterLineByAllRoad(PointF fpt,PointF lpt)//全路径栅格化 { float Xabs = Math.Abs(lpt.X - fpt.X); float Yabs = Math.Abs(lpt.Y - fpt.Y); int i1 = (int)(fpt.Y / 10); int j1=(int)(fpt.X/10); int i2 = (int)(lpt.Y / 10); int j2=(int)(lpt.X/10); int m=10;//网格大小 int y0=this.pictureBox1.Height; int Row = (int)y0 / 10; int x0=this.pictureBox1.Width; int Col = (int)x0 / 10; if (Xabs >= Yabs) //列数大于行数 { int sign = 0; if(Xabs !=0) { float tan = (lpt.Y - fpt.Y) / (lpt.X - fpt.X); if (lpt.Y>fpt.Y) //i1 fpt.X) //j1= j2) je = j2; Rasterfromto(sign,i, ja, je); ja = je;

} } else //j1>j2 { for (int i = i1; i <= i2;i++ ) { int je = Convert.ToInt32((((i + 1) * m - fpt.Y) / tan + fpt.X) / m); if (je <= j2) je = j2; Rasterfromto(sign, i, ja, je); ja = je; } } } else //i1>i2 { int ja = j2; if (lpt.X > fpt.X) //j1j2 { for (int i = i2; i <= i1; i++) { int je = Convert.ToInt32((((i + 1) * m - lpt.Y) / tan + lpt.X) / m); if (je >= j1) je = j1; Rasterfromto(sign, i, ja, je); ja = je; } } } } else //水平线 i1=i2 { Rasterfromto(sign, i1, j1, j2);

} } else //行数大于列数 { int sign = 1; if (Yabs != 0) { float tan = (lpt.X - fpt.X) / (lpt.Y - fpt.Y); if (lpt.X < fpt.X) //j1>j2 { int ia = i2; if (lpt.Y > fpt.Y) //i1i2 { for (int j = j2; j <= j1; j++) { int ie = Convert.ToInt32((((j + 1) * m - lpt.X) / tan + lpt.Y) / m); if (ie >= i1) ie = i1; Rasterfromto(sign, j, ia, ie); ia = ie; } } } else //j1 fpt.Y) //i1= i2) ie = i2;

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地理信息系统算法题——C#.pdf

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