[英]Rotate meshgrid with numpy
我想生成一个坐标已旋转的网格。 我必须在双循环中进行旋转,而且我确信有更好的方法对其进行矢量化。 代码是这样的:
# Define the range for x and y in the unrotated matrix
xspan = linspace(-2*pi, 2*pi, 101)
yspan = linspace(-2*pi, 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,j], y[i,j]]))
# Now the matrix is rotated
return xrot, yrot
# Pick some arbitrary function and plot it (no rotation)
x, y = DoRotation(xspan, yspan, 0)
z = sin(x)+cos(y)
imshow(z)
# And now with 0.3 radian rotation so you can see that it works.
x, y = DoRotation(xspan, yspan, 0.3)
z = sin(x)+cos(y)
figure()
imshow(z)
必须在两个网格上编写双循环似乎很愚蠢。 那里的一位向导知道如何对其进行矢量化吗?
也许我误解了这个问题,但我通常只是......
import numpy as np
pi = np.pi
x = np.linspace(-2.*pi, 2.*pi, 1001)
y = x.copy()
X, Y = np.meshgrid(x, y)
Xr = np.cos(rot)*X + np.sin(rot)*Y # "cloclwise"
Yr = -np.sin(rot)*X + np.cos(rot)*Y
z = np.sin(Xr) + np.cos(Yr)
〜100ms也
爱因斯坦求和( np.einsum
)对于这种事情非常快。 1001x1001我得到97毫秒。
def DoRotation(xspan, yspan, RotRad=0):
"""Generate a meshgrid and rotate it by RotRad radians."""
# Clockwise, 2D rotation matrix
RotMatrix = np.array([[np.cos(RotRad), np.sin(RotRad)],
[-np.sin(RotRad), np.cos(RotRad)]])
x, y = np.meshgrid(xspan, yspan)
return np.einsum('ji, mni -> jmn', RotMatrix, np.dstack([x, y]))
你可以摆脱这两个嵌套的循环, flattening with np.ravel
进行一些reshaping
和展flattening with np.ravel
并保持矩阵乘法与np.dot
一样 -
mult = np.dot( RotMatrix, np.array([x.ravel(),y.ravel()]) )
xrot = mult[0,:].reshape(xrot.shape)
yrot = mult[1,:].reshape(yrot.shape)
以防万一您想要 go 换成3D,scipy.spatial.transform.Rotation可能会有用
import numpy as np
from scipy.spatial.transform import Rotation as R
# define lines for x- and y-subdivision
x = np.linspace(-5, 5)
y = np.linspace(-5, 5)
# create meshgrid for a plane surface (just as example)
X, Y = np.meshgrid(x, y)
Z = np.zeros(X.shape) # alternatively Z may come from a 3D-meshgrid
# define rotation by rotation angle and axis, here 45DEG around z-axis
r = R.from_rotvec(np.pi/4 * np.array([0, 0, 1]))
# arrange point coordinates in shape (N, 3) for vectorized processing
XYZ = np.array([X.ravel(), Y.ravel(), Z.ravel()]).transpose()
# apply rotation
XYZrot = r.apply(XYZ)
# return to original shape of meshgrid
Xrot = XYZrot[:, 0].reshape(X.shape)
Yrot = XYZrot[:, 1].reshape(X.shape)
Zrot = XYZrot[:, 2].reshape(X.shape)
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