python – 用numpy旋转网格

发布时间：2020-12-20 11:42:20 所属栏目：Python 来源：网络整理

导读：我想要生成一个坐标已旋转的网格.我必须在双循环中进行旋转,我确信有更好的方法来矢量化它.代码如下： # Define the range for x and y in the unrotated matrixxspan = linspace(-2*pi,2*pi,101)yspan = linspace(-2*pi,101)# Generate a meshgrid and rota

我想要生成一个坐标已旋转的网格.我必须在双循环中进行旋转,我确信有更好的方法来矢量化它.代码如下：

# Define the range for x and y in the unrotated matrix
xspan = linspace(-2*pi,2*pi,101)
yspan = linspace(-2*pi,101)

# Generate a meshgrid and rotate it by RotRad radians.
def DoRotation(xspan,yspan,RotRad=0):

    # Clockwise,2D rotation matrix
    RotMatrix = np.array([  [np.cos(RotRad),np.sin(RotRad)],[-np.sin(RotRad),np.cos(RotRad)]])
    print RotMatrix

    # This makes two 2D arrays which are the x and y coordinates for each point.
    x,y = meshgrid(xspan,yspan)

    # After rotating,I'll have another two 2D arrays with the same shapes.
    xrot = zeros(x.shape)
    yrot = zeros(y.shape)

    # Dot the rotation matrix against each coordinate from the meshgrids.
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    # I BELIEVE THERE IS A BETTER WAY THAN THIS DOUBLE LOOP!!!
    for i in range(len(xspan)):
        for j in range(len(yspan)):
            xrot[i,j],yrot[i,j] = dot(RotMatrix,array([x[i,y[i,j]]))

    # Now the matrix is rotated
    return xrot,yrot

# Pick some arbitrary function and plot it (no rotation)
x,y = DoRotation(xspan,0)
z = sin(x)+cos(y)
imshow(z)

# And now with 0.3 radian rotation so you can see that it works.
x,0.3)
z = sin(x)+cos(y)
figure()
imshow(z)

在两个网格物体上写一个双循环似乎很愚蠢.那里的一个巫师有一个想法如何矢量化这个？

解决方法

爱因斯坦求和( np.einsum)对于这种事情非常快. 1001×1001我得到97毫秒.

def DoRotation(xspan,RotRad=0):
    """Generate a meshgrid and rotate it by RotRad radians."""

    # Clockwise,2D rotation matrix
    RotMatrix = np.array([[np.cos(RotRad),np.cos(RotRad)]])

    x,y = np.meshgrid(xspan,yspan)
    return np.einsum('ji,mni -> jmn',RotMatrix,np.dstack([x,y]))

（编辑：李大同）

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