Create a poly line from point data

[laserman781]

I am trying to plot a polyline rather than simply plotting the points. I was able to plot a spline but this is not what I want. How can I accomplish this?

This is what I have written so far:

xyz = pd.read_csv('line_points.csv')
coords = xyz[['x', 'y', 'z']].values
poly = pv.PolyData(coords)
spline = pv.Spline(coords)
poly.plot(show_grid=False, point_size=3, color='red')
spline.plot(show_grid=False, point_size=3, color='white')

[banesullivan]

Hi @laserman781 - this question is more appropriate for the pyvista-support repository, so I am moving it there shortly.

The code you have looks appropriate for plotting a PolyLine - using pv.Spline is the right choice. Unfortunately, there isn't much more I can offer without seeing visualizations of why the spline is not what you want or without having the csv file you read.

My guess is that the Spline looks wacky because the points in your csv file are not ordered - you'll likely need to make sure the points are ordered for the PolyLine/Spline to work.

[laserman781]

@banesullivan The spline comes out correctly with pv.Spline, although I want to avoid the interpolation of spline. Any suggestions?

[banesullivan]

Ah yes, the Spline is parametric and interpolates the points which might not be desired.

Try this solution with lines_from_points():

import pyvista as pv
import numpy as np
pv.set_plot_theme('doc')

def make_points():
    """Helper to make XYZ points"""
    theta = np.linspace(-4 * np.pi, 4 * np.pi, 100)
    z = np.linspace(-2, 2, 100)
    r = z**2 + 1
    x = r * np.sin(theta)
    y = r * np.cos(theta)
    return np.column_stack((x, y, z))


def lines_from_points(points):
    """Given an array of points, make a line set"""
    poly = pv.PolyData()
    poly.points = points
    cells = np.full((len(points)-1, 3), 2, dtype=np.int)
    cells[:, 1] = np.arange(0, len(points)-1, dtype=np.int)
    cells[:, 2] = np.arange(1, len(points), dtype=np.int)
    poly.lines = cells
    return poly

points = make_points()

line = lines_from_points(points)

p = pv.Plotter()
p.add_mesh(points, color='red')
p.add_mesh(line, color='blue',)
p.show()

[banesullivan]

Also, note that a very similar function exists in PyVista: https://docs.pyvista.org/utilities/utilities.html#pyvista.lines_from_points

However, it requires the points array to be explicit about which lines make each segment - if the points are already ordered, then you can probably stick with the method I shared in the post above.

[laserman781]

@banesullivan This is excellent information thank you!

[banesullivan]

I'm assuming this solution worked? If so, would you please close the issue?