拥有一条跟随另一条路径的路径

我有一个坐标数组（地理坐标，但这无关紧要），我需要一个“跟随”我们已经拥有的路径的路径。

我们需要类似下图所示的内容。 您可以看到路径不完全相同（不是简单的偏移），我们也不希望它也可以缩放。

是否有一些我们可以用来做这个的库或一些关于如何实现它的指针？

Answer 1

花了太多时间试图找到一个有效的解决方案后，我最终编写了自己的代码：

CGContextBeginPath(context); CGMutablePathRef path = CGPathCreateMutable(); MKMapPoint *mapPoints = itineraryPath.points; CGPoint previousEdgeNormal = CGPointZero; CGPoint previousDrawnPoint = CGPointZero; float offsetDistance = self.pathWidth*2.5; for(int i = 0; i < itineraryPath.pointCount; i++) { if(i < itineraryPath.pointCount-1) { MKMapPoint mapPoint = mapPoints[i]; CGPoint point = [self pointForMapPoint:mapPoint]; MKMapPoint secondMapPoint = mapPoints[i+1]; CGPoint secondPoint = [self pointForMapPoint:secondMapPoint]; float xDelta = point.x-secondPoint.x; float yDelta = point.y-secondPoint.y; float factor = xDelta > 0 ? -1 : 1; float segmentLength = sqrt(pow(xDelta, 2.0)+pow(yDelta, 2.0)); float yDeltaAngle = asin(sin(M_PI/2*factor)*yDelta/segmentLength); float opposedAngle = M_PI/2-yDeltaAngle; float remainingAngle = M_PI/2-opposedAngle; float yOffset = sin(opposedAngle)*offsetDistance/sin(M_PI/2)*factor; float xOffset = sin(remainingAngle)*offsetDistance/sin(M_PI/2)*factor; CGPoint offsetFirstPoint = CGPointMake(point.x+xOffset, point.y+yOffset); CGPoint offsetSecondPoint = CGPointMake(secondPoint.x+xOffset, secondPoint.y+yOffset); if(i == mapPointIndex) { CGPathMoveToPoint(path, NULL, offsetFirstPoint.x, offsetFirstPoint.y); previousDrawnPoint = offsetFirstPoint; } else { float xNormalDifference = previousEdgeNormal.x-offsetFirstPoint.x; float yNormalDifference = previousEdgeNormal.y-offsetFirstPoint.y; float xAverage = (xNormalDifference)/2; float yAverage = (yNormalDifference)/2; CGPoint normalAveragePoint = CGPointMake(offsetFirstPoint.x+xAverage, offsetFirstPoint.y+yAverage); CGPathAddLineToPoint(path, NULL, normalAveragePoint.x, normalAveragePoint.y); previousDrawnPoint = normalAveragePoint; } previousEdgeNormal = offsetSecondPoint; } else CGPathAddLineToPoint(path, NULL, previousEdgeNormal.x, previousEdgeNormal.y); } 

唯一需要注意的是，它还没有很好地处理锐角。

但是否则会给出一些非常整洁的东西（右边是原始路径，左边是偏移）

地图http://sofzh.miximages.com/iphone/Screen Shot 2013-03-08 at 5.45.34 AM.png

Answer 2

您想要的是一条平行曲线： http ： //en.wikipedia.org/wiki/Parallel_curve

生成它的一种方法是计算每个点处原始曲线的法线，然后使用该法线偏移这些点。 如果您只有直线段，这很简单。 对于弧和贝塞尔曲线，您还需要弄清楚如何修改控制点。