[ENH]: FancyArrow in 3D

Problem

Hello,

FancyArrow can not be used in 3D.
Some proposals (#21688) consists in creating a new class.
Could it be possible:

to extend FancyArrow to 3D (as for quiver)
to solve -if possible- the arrow head problem representation when loocking the arrow along its axis (see the 2nd plot in the figure below)

Thanks,
Patrick

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import FancyArrowPatch, FancyArrow
from mpl_toolkits.mplot3d import proj3d


class Arrow3D(FancyArrowPatch):
    """ Create fancy arrow (artist) for 3d matplotlib visualisation """

    def __init__(self, xs, ys, zs, *args, **kwargs):
        FancyArrowPatch.__init__(self, (0, 0), (0, 0), *args, **kwargs)
        self._verts3d = xs, ys, zs

    def draw(self, renderer):
        xs3d, ys3d, zs3d = self._verts3d
        xarr, yarr, _ = proj3d.proj_transform(xs3d, ys3d, zs3d, self.axes.M)
        self.set_positions((xarr[0], yarr[0]), (xarr[1], yarr[1]))
        FancyArrowPatch.draw(self, renderer)


fig, ax = plt.subplots(1, 2, figsize=(12, 5),
                       subplot_kw=dict(projection="3d",
                                       proj_type='ortho'))

ax[0].voxels(np.ones((1, 1, 1)), facecolors=[0, 0, 0, 0], edgecolors='k')
# ax[0].add_artist(FancyArrow(0, 0, 0, 1, 1, 1))
ax[0].add_artist(Arrow3D((0, 1), (0, 1), (0, 1), mutation_scale=50))

ax[1].voxels(np.ones((1, 1, 1)), facecolors=[0, 0, 0, 0], edgecolors='k')
ax[1].view_init(elev=28, azim=45)
# ax[1].add_artist(FancyArrow(0, 0, 0, 1, 1, 1)))
ax[1].add_artist(Arrow3D((0, 1), (0, 1), (0, 1), mutation_scale=50))

plt.show()

Proposed solution

No response

@patquem

@patquem Can u give some insight s on how to solve this issue

Adding Arrow3D class in mplot3d, this should be easy :) .
Solving the arrow head problem during visualization, I have no idea how to fix that. Sorry :( .

@soma2000-lang

Hello @soma2000-lang
introducing the penultimate line in the code (if not....) avoids a warning message and drawing the wrong arrowhead as mentioned above. Not sure if this is the right way to fix the bug, but temporarily it might be a solution.
Patrick

class Arrow3D(FancyArrowPatch):
    """ Create fancy arrow (artist) for 3d matplotlib visualisation """

    def __init__(self, xs, ys, zs, *args, **kwargs):
        FancyArrowPatch.__init__(self, (0, 0), (0, 0), *args, **kwargs)
        self._verts3d = xs, ys, zs

    def draw(self, renderer):
        xs3d, ys3d, zs3d = self._verts3d
        xarr, yarr, _ = proj3d.proj_transform(xs3d, ys3d, zs3d, self.axes.M)
        self.set_positions((xarr[0], yarr[0]), (xarr[1], yarr[1]))
        if not (np.allclose(xarr, 0.) and np.allclose(yarr, 0.)):
            FancyArrowPatch.draw(self, renderer)

Hi, is anyone working on this ? I know you don't assign issues but I would like to try it !

@soma2000-lang

I believe that maybe @soma2000-lang is not actively working on this, so please give it a go!

I have labeled this a a good first issue because there is ~working code for the implementation, but medium because it involves (limited) API design.

This will need:

a method added to Axes3D
- numpydoc style docstring
- tests
get to a consensus on the API (which in addition to the actually time it takes to have the conversation may take very long in calendar time)
a whats-new entry
an example in the gallery

This is a good project for someone with library design experience but who is new to Matplotlib.

So I'm just gonna throw out this sketch because the signature is closer to FancyArrowPatch

class FancyArrowPatch3D(mpatches.FancyArrowPatch):
    def __init__(self, posA, posB, *args, **kwargs):
        mpatches.FancyArrowPatch.__init__(self, (0, 0), (0, 0), *args, **kwargs)
        self._verts3d = list(zip(posA, posB))

@tacaswell

Here is a function based on the solution from @tacaswell which takes an array of arrow start points and endpoints. Additionally, it sets the axes limits so that all start/end points remain visible.

def arrows3d(ends, starts=None, ax=None, label=None, **kwargs):
    """3D plot of multiple arrows

    Args:
        ends (ndarray): (N, 3) size array of arrow end coordinates
        starts (ndarray): (N, 3) size array of arrow start coordinates.
            Assume start position of (0, 0, 0) if not given
        ax (Axes3DSubplot): existing axes to add to
        label (str): legend label to apply to this group of arrows
        kwargs (dict): additional arrow properties
    """
    if starts is None:
        starts = np.zeros_like(ends)

    assert starts.shape == ends.shape, "`starts` and `ends` shape must match"
    assert len(ends.shape) == 2 and ends.shape[1] == 3, \
        "`starts` and `ends` must be shape (N, 3)"

    class Arrow3D(FancyArrowPatch):
        def __init__(self, xs, ys, zs, *args, **kwargs):
            super().__init__((0,0), (0,0), *args, **kwargs)
            self._verts3d = xs, ys, zs

        def do_3d_projection(self, renderer=None):
            xs3d, ys3d, zs3d = self._verts3d
            xs, ys, zs = proj3d.proj_transform(xs3d, ys3d, zs3d, self.axes.M)
            self.set_positions((xs[0],ys[0]),(xs[1],ys[1]))

            return np.min(zs)

    # create new axes if none given
    if ax is None:
        ax = plt.figure().add_subplot(111, projection='3d')

    arrow_prop_dict = dict(mutation_scale=20, arrowstyle='-|>', color='k', shrinkA=0, shrinkB=0)
    arrow_prop_dict.update(kwargs)
    for ind, (s, e) in enumerate(np.stack((starts, ends), axis=1)):
        a = Arrow3D(
            [s[0], e[0]], [s[1], e[1]], [s[2], e[2]],
            # only give label to first arrow
            label=label if ind == 0 else None,
            **arrow_prop_dict
        )
        ax.add_artist(a)

    # store starts/ends on the axes for setting the limits
    ax.points = np.vstack((starts, ends, getattr(ax, 'points', np.empty((0, 3)))))
    ax.set_xlim3d(ax.points[:, 0].min(),ax.points[:, 0].max())
    ax.set_ylim3d(ax.points[:, 1].min(),ax.points[:, 1].max())
    ax.set_zlim3d(ax.points[:, 2].min(),ax.points[:, 2].max())

    return ax

ax = arrows3d(np.random.normal(size=(5, 3)), label='Foo')
ax = arrows3d(np.random.normal(size=(5, 3)), ax=ax, color='r',label='Bar')
plt.legend()
plt.show()

@patquem

heyy @patquem looking to the issue , seems like it can be done.
Let me work on this issue and fix it.

@ShubhamPatel-16

@ShubhamPatel-16 this issue can't be moved forward until decisions are made in #22435 b/c this API should match that one as much as possible.

Removing the good first issue label for now b/c this isn't ready for work yet.

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[ENH]: FancyArrow in 3D #22571

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[ENH]: FancyArrow in 3D #22571

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soma2000-lang commented on Mar 1, 2022

patquem commented on Mar 1, 2022

patquem commented on Mar 7, 2022

AnnaMastori commented on Apr 19, 2022

oscargus commented on Apr 19, 2022

tacaswell commented on Aug 26, 2022

story645 commented on Dec 20, 2022

Evidlo commented on Jan 10, 2023

ShubhamPatel-16 commented on Mar 10, 2026

story645 commented on Mar 10, 2026

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