线旋转问题

Question

我有两条线是这样画的：

float Alpha = RotDegrees;
PointF PitCenter = new Point(picBoxZoomMap.Width / 2, picBoxZoomMap.Height / 2);
PointF p = new PointF(PitCenter.X - 20, PitCenter.Y - 250);
PointF p2 = new PointF(PitCenter.X + 20, PitCenter.Y - 250);

zoomgfx.DrawLine(Pens.Red, PitCenter, new PointF(
    (float)((p.Y - PitCenter.Y) * Math.Sin(Alpha * Math.PI / 180) + p.X),
    (float)(PitCenter.Y + (p.Y - PitCenter.Y) * Math.Cos(Alpha * Math.PI / 180))));

zoomgfx.DrawLine(Pens.Red, PitCenter, new PointF(
    (float)((p2.Y - PitCenter.Y) * Math.Sin(Alpha * Math.PI / 180) + p2.X),
    (float)(PitCenter.Y + (p2.Y - PitCenter.Y) * Math.Cos(Alpha * Math.PI / 180))));

这里是 Alpha = 0 时的行；

这是旋转 90 度后的线条..

正如你所看到的那样，线条以某种方式相遇..我真的不明白为什么.. 有什么想法吗？

Answer 1

您的旋转公式不正确，请看这里 --> Rotate a point by another point in 2D

把你的代码改成这样，你会得到正确的效果：

PointF PitCenter = new Point(picBoxZoomMap.Width / 2, picBoxZoomMap.Height / 2);
PointF p = new PointF(PitCenter.X - 20, PitCenter.Y - 250);
PointF p2 = new PointF(PitCenter.X + 20, PitCenter.Y - 250);

var AlphaRad = RotDegrees * Math.PI / 180;

zoomgfx.DrawLine(Pens.Red, PitCenter, new PointF(
(float)(Math.Cos(AlphaRad) * (p.X - PitCenter.X) - Math.Sin(AlphaRad) * (p.Y - PitCenter.Y) + PitCenter.X),
(float)(Math.Sin(AlphaRad) * (p.X - PitCenter.X) + Math.Cos(AlphaRad) * (p.Y - PitCenter.Y) + PitCenter.Y)));

zoomgfx.DrawLine(Pens.Red, PitCenter, new PointF(
(float)(Math.Cos(AlphaRad) * (p2.X - PitCenter.X) - Math.Sin(AlphaRad) * (p2.Y - PitCenter.Y) + PitCenter.X),
(float)(Math.Sin(AlphaRad) * (p2.X - PitCenter.X) + Math.Cos(AlphaRad) * (p2.Y - PitCenter.Y) + PitCenter.Y)));

Answer 2

你取 Y 坐标之间的差值并乘以 Sin 得到 X 坐标。这是正确的。

但是，当您构建新的 Y 坐标时，您也会获取 Y 坐标之间的差异。为此，您应该取 X 坐标之间的差值并乘以 Cos。

例如您的第 8 行和第 12 行为新点生成相同的 Y 坐标，因为 p.Y - PitCenter.Y 与 p2.Y - PitCenter.Y 相同，因为 p.Y = p2.Y。

有道理吗？

Answer 3

我发现如果我把它分解得更容易理解。在我看来，你试图同时做太多事情。我认为这会满足您的要求（我不确定半径定义是否正是您想要的），但希望它足够清晰，您可以理解我的建议。

float RotDegrees = 90.0;              // Centerline angle for wedge
float width = 10.0;                   // Assume a 10 degree wedge

// Center of view
PointF PitCenter = new PointF(picBoxZoomMap.Width / 2,
                              picBoxZoomMap.Height / 2);

// Determine the angle for the wedges in radians
float theta0 = (RotDegrees - width / 2.0) * Math.PI / 180.0;
float theta1 = (RotDegrees + width / 2.0) * Math.PI / 180.0;

// May need to adjust this to satisfy your needs 
float radius = 100.0;

// Determine the endpoints of the new wedge ... Assumes (0,0) is in the upper
// left corner rather than the lower left (where it belongs ;).  If it's in the
// lower left after all, change the subtraction in the Y components to an
// addition
PointF p0 = new PointF( PitCenter.X + radius * Math.Cos(theta0),
                        PitCenter.Y - radius * Math.Sin(theta0) );

PointF p1 = new PointF( PitCenter.X + radius * Math.Cos(theta1),
                        PitCenter.Y - radius * Math.Sin(theta1));

// Draw the lines
zoomgfx.DrawLine(Pens.Red, PitCenter, p0);
zoomgfx.DrawLine(Pens.Red, PitCenter, p1);