Mayavi: Rotate Around Y Axis

I'm plotting a 3D mesh using mayavi's triangular_mesh method. The data describes a human silhouette laying face-down in 3D space (so the cmap can be used to denote distance from th

Solution 1:

It turns out there's a bit of a workaround for this.

You can rotate the actors on their axes independently of the camera. (This throws the visualization out of step with the data labeling, but as I'm actually hiding the axes of the figure it doesn't matter in this case.)

All you need to do is:

m.actor.actor.rotate_y(desired_angle)

...and you're good to go.

Solution 2:

You need some math here. Ok, here is how to do it in terms of code, its not the best code but I wanted to make it self-explanatory. I use the Rodrigues formula for rotation in 3d to achieve this, az_new and el_new are your new viewing angles. Change the value of theta to get a different viewing angle in your frame of reference, i have used 45 degrees in the code below:

import numpy as np
import math

def rotation_matrix(axis, theta):
    """
    Return the rotation matrix associated with counterclockwise rotation about
    the given axis by theta radians.
    """
    axis = np.asarray(axis)
    theta = np.asarray(theta)
    axis = axis/math.sqrt(np.dot(axis, axis))
    a = math.cos(theta/2.0)
    b, c, d = -axis*math.sin(theta/2.0)
    aa, bb, cc, dd = a*a, b*b, c*c, d*d
    bc, ad, ac, ab, bd, cd = b*c, a*d, a*c, a*b, b*d, c*d
    return np.array([[aa+bb-cc-dd, 2*(bc+ad), 2*(bd-ac)],
                     [2*(bc-ad), aa+cc-bb-dd, 2*(cd+ab)],
                     [2*(bd+ac), 2*(cd-ab), aa+dd-bb-cc]])


az = 90
el = -75

x = np.cos(np.deg2rad(el))*np.cos(np.deg2rad(az))
y = np.cos(np.deg2rad(el))*np.sin(np.deg2rad(az))
z = np.sin(np.deg2rad(el))

# So your viewing vector in x,y coordinates on unit sphere
v = [x,y,z]

# Since you want to rotate about the y axis from this viewing angle, we just increase the# elevation angle by 90 degrees to obtain our axis of rotation

az2 = az
el2 = el+90

x = np.cos(np.deg2rad(el2))*np.cos(np.deg2rad(az2))
y = np.cos(np.deg2rad(el2))*np.sin(np.deg2rad(az2))
z = np.sin(np.deg2rad(el2))

axis = [x,y,z]

# Now to rotate about the y axis from this viewing angle we use the rodrigues formula# We compute our new viewing vector, lets say we rotate by 45 degrees
theta = 45
newv = np.dot(rotation_matrix(axis,np.deg2rad(theta)), v)

#Get azimuth and elevation for new viewing vector
az_new = np.rad2deg(np.arctan(newv[1]/newv[0]))
el_new = np.rad2deg(np.arcsin(newv[2]))