python - Specify absolute colour for 3D points in MayaVi

Question

I am using the MayaVi Python library to plot 3d points, using the points3d class. The documentation specifies that the colour of each point is specified through a fourth argument, s:

In addition, you can pass a fourth array s of the same shape as x, y, and z giving an associated scalar value for each point, or a function f(x, y, z) returning the scalar value. This scalar value can be used to modulate the color and the size of the points.

This specifies a scalar value for each point, which maps the point to a colourmap, such as copper, jet or hsv. E.g. from their documentation:

import numpy
from mayavi.mlab import *

def test_points3d():
    t = numpy.linspace(0, 4*numpy.pi, 20)
    cos = numpy.cos
    sin = numpy.sin

    x = sin(2*t)
    y = cos(t)
    z = cos(2*t)
    s = 2+sin(t)

    return points3d(x, y, z, s, colormap="copper", scale_factor=.25)

Gives:

Instead, I would like to specify the actual value for each point as an (r, g, b) tuple. Is this possible in MayaVi? I have tried replacing the s with an array of tuples, but an error is thrown.

Answer 1

After struggling with this for most of today, I found a relatively simple way to do exactly what the question asks -- specify an RGB tuple for each point. The trick is just to define a color map with exactly the same number of entries as there are points to plot, and then set the argument to be a list of indices:

# Imports
import numpy as np
from mayavi.mlab import quiver3d, draw

# Primitives
N = 200 # Number of points
ones = np.ones(N)
scalars = np.arange(N) # Key point: set an integer for each point

# Define color table (including alpha), which must be uint8 and [0,255]
colors = (np.random.random((N, 4))*255).astype(np.uint8)
colors[:,-1] = 255 # No transparency

# Define coordinates and points
x, y, z = colors[:,0], colors[:,1], colors[:,2] # Assign x, y, z values to match color
pts = quiver3d(x, y, z, ones, ones, ones, scalars=scalars, mode='sphere') # Create points
pts.glyph.color_mode = 'color_by_scalar' # Color by scalar

# Set look-up table and redraw
pts.module_manager.scalar_lut_manager.lut.table = colors
draw()