spline_plotting.md

Visualizing Splines

As a new feature splinepy now also has the ability to directly plot splines. The splines are plotted with the library gustaf and vedo.

The following will give a brief introduction into basic spline creation and visualization.

Creating a basic NURBS

For example here we will be creating a hollow disk of 120 degrees explicitly as a NURBS.

import splinepy

# create a 2D NURBS disk and visualize
nurbs = splinepy.NURBS(
    degrees=[1, 2],
    knot_vectors=[[0, 0, 1, 1], [0, 0, 0, 1, 1, 2, 2, 2]],
    control_points=[
        [5.00000000e-01, 0.00000000e00],
        [1.00000000e00, 0.00000000e00],
        [5.00000000e-01, 2.88675135e-01],
        [1.00000000e00, 5.77350269e-01],
        [2.50000000e-01, 4.33012702e-01],
        [5.00000000e-01, 8.66025404e-01],
        [0.00000000e00, 5.77350269e-01],
        [0.00000000e00, 1.15470054e00],
        [-2.50000000e-01, 4.33012702e-01],
        [-5.00000000e-01, 8.66025404e-01],
    ],
    weights=[
        [1.0],
        [1.0],
        [0.8660254],
        [0.8660254],
        [1.0],
        [1.0],
        [0.8660254],
        [0.8660254],
        [1.0],
        [1.0],
    ],
)

nurbs.show()

Creation of common geometries

You might think well this is a lot of code and you are right, that is why splinepy provides powerful functions to create splines on the fly. To show this next the same geometry is created with a single command.

easy_disk = splinepy.helpme.create.disk(
    outer_radius=1,
    inner_radius=0.5,
    angle=120,
    n_knot_spans=2,
)

gus.show(
    ["Handmade disk", nurbs],
    ["Easy disk", easy_disk],
)

That was much easier. Feel free to peruse the helpful functions in splinepy.helmpe.

Expanding into 3D

You can also extrude and revolve spline with the build in Creator class.

extruded = nurbs.create.extruded(extrusion_vector=[0, 0, 1])
revolved = nurbs.create.revolved(axis=[1, 0, 0], angle=70)

gus.show(
    ["Extruded NURBS", extruded],
    ["Revolved NURBS", revolved],
)

This does not need to be only from 2D->3D but can also be from 1D->2D etc.

This is just the beginning of what you can do with the given plotting and creation capabilities in this library. Please look into the examples folder to see more capabilities.

Notebook plotting

You can also plot your splines inside a notebook. For this you need to change the vedo backend to 'k3d'. To do this you need to add the following lines to the top of the notebook.

import vedo

vedo.settings.default_backend = "k3d"

After this most functionality of the normal plotting should be available to you. Please write an issue if you find something that you can plot in a script but not in a notebook. There is one known issue regarding number of Line objects that we can plot (limited to 200 from vedo). We are working on a solution, but meanwhile, plotting curves is limited to resolutions of 201; for 2D/3D splines you can turn off knots in show_options. An example is provided in the folder examples/ipynb.