google map 地图轨迹点以画带箭头的直线连接，直观轨迹记录。

       一般我们在做地图定位或轨迹查询的时候，需要在地图上绘画各个轨迹点的marker，然后记录各marker点的经纬度坐标，通过drawLine或drawPath可以把各个点连接起来，以实现轨迹记录。

       但是我们想如果这条线能从起始点的marker到中途以及最后点的marker能有一条带箭头的直线连接起来，这样用户看起来更直观一点，一眼就能看懂起始点和终点的线路。这样就需要我们判断直线所画的方向和中途marker点的位置，然后延伸画两条小线，以实现箭头的效果。

	class LineOverlay extends Overlay {/*** according two GeoPoint, draw a line.(use in track)* must have frontGeopoint and backGeopoint  */private GeoPoint front;private GeoPoint back;Paint paint;public LineOverlay() {}public LineOverlay(GeoPoint front, GeoPoint back) {this.front = front;this.back = back;}public void draw(Canvas canvas, MapView mapview, boolean shadow) {super.draw(canvas, mapview, shadow);paint = new Paint();paint.setColor(Color.BLUE);paint.setStyle(Paint.Style.FILL_AND_STROKE);paint.setStrokeWidth(2);paint.setAntiAlias(true);Point point_f = new Point();Point point_b = new Point();//Path path = new Path();mapview.getProjection().toPixels(front, point_f);mapview.getProjection().toPixels(back, point_b);// begin//path.moveTo(point_b.x, point_b.y);// end//path.lineTo(point_f.x, point_f.y);//canvas.drawPath(path, paint);//JudgeDrawArrow(canvas, point_b.x, point_b.y, point_f.x, point_f.y);JudgeDrawArrow(canvas, point_f.x, point_f.y, point_b.x, point_b.y);}/** x1 is the first geopoint marker point X,y1 is that Y;* x2 is the second geopoint marker point X,y2 is that Y;* judge and draw arrow line*/public void JudgeDrawArrow(Canvas canvas, int x1, int y1, int x2, int y2) {double arrow_height = 10; // 箭头高度  double arrow_btomline = 7; // 底边的一半  int x3 = 0;  int y3 = 0;  int x4 = 0;  int y4 = 0;double arctangent = Math.atan(arrow_btomline / arrow_height); // 箭头角度  double arrow_len = Math.sqrt(arrow_btomline * arrow_btomline + arrow_height * arrow_height); // 箭头的长度  double[] endPoint_1 = rotateVec(x2 - x1, y2 - y1, arctangent, true,  arrow_len);double[] endPoint_2 = rotateVec(x2 - x1, y2 - y1, -arctangent, true,  arrow_len);double x_3 = x2 - endPoint_1[0]; // (x_3,y_3)是第一端点  double y_3 = y2 - endPoint_1[1];  double x_4 = x2 - endPoint_2[0]; // (x_4,y_4)是第二端点  double y_4 = y2 - endPoint_2[1];  Double X3 = new Double(x_3);x3 = X3.intValue();  Double Y3 = new Double(y_3);  y3 = Y3.intValue();  Double X4 = new Double(x_4);  x4 = X4.intValue();  Double Y4 = new Double(y_4);  y4 = Y4.intValue();  // 画线  canvas.drawLine(x1, y1, x2, y2,paint);  // 画箭头的一半  canvas.drawLine(x2, y2, x3, y3,paint);  // 画箭头的另一半  canvas.drawLine(x2, y2, x4, y4,paint);  }  public double[] rotateVec(int px, int py, double ang, boolean isChlen,double newLen) {  double rotateResult[] = new double[2];  // 矢量旋转函数，参数含义分别是x分量、y分量、旋转角、是否改变长度、新长度  double vx = px * Math.cos(ang) - py * Math.sin(ang);  double vy = px * Math.sin(ang) + py * Math.cos(ang);  if (isChlen) {  double d = Math.sqrt(vx * vx + vy * vy);  vx = vx / d * newLen;  vy = vy / d * newLen;  rotateResult[0] = vx;  rotateResult[1] = vy;  }  return rotateResult;  }}

point_f.X,Y为marker点1的屏幕坐标点，point_b.X,Y为marker点2的屏幕坐标点。

（效果图）

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