# [Matplotlib-users] How to draw a collection of oriented triangles ?

Joshua Klein mobiusklein at gmail.com
Sat Nov 26 15:47:35 EST 2016

```I don’t think my code ever directly works with a PatchCollection object,
just individual patches which possess distinct properties. Here’s an
example using animations:

import matplotlib
matplotlib.use("Tkagg")from matplotlib import pyplot as pltfrom
matplotlib.path import Pathfrom matplotlib.transforms import
Affine2Dfrom matplotlib.patches import PathPatchfrom matplotlib import
animationimport numpy as np

unit_triangle = Path.unit_regular_polygon(3)
def make_triangle(x, y, rot_deg, color, scale):
path = Path(unit_triangle.vertices * scale, unit_triangle.codes)
trans = Affine2D().translate(x, y).rotate_deg_around(x, y, rot_deg)
t_path = path.transformed(trans)
patch = PathPatch(t_path, facecolor=color)
return patch

triangles = [(1, 1, 90), (2, 2, 45), (-1, 1, 128)]
patches = []
def step_fn(i):
next_step = []
# Random walk update each triangle's position
for tri in triangles:
x = tri[0] + np.random.random() - 0.5
y = tri[1] + np.random.random() - 0.5
rot = tri[2] + (np.random.random() - 0.5) * 45
next_step.append((x, y, rot))
triangles[:] = next_step

# Remove the old patches
while patches:
patch = patches.pop()
patch.remove()

patches[:] = [make_triangle(x, y, rot_deg, "blue", 0.2) for x, y,
rot_deg in triangles]
for patch in patches:
plt.autoscale()

fig = plt.figure()
a = animation.FuncAnimation(fig, step_fn, blit=False, interval=10)

plt.show()

​

On Sat, Nov 26, 2016 at 12:20 PM, Nicolas P. Rougier <
Nicolas.Rougier at inria.fr> wrote:

>
> Thank you Joshua, I'll start from your code. My other problem is that I
> also need to update rotation and position (for an animation). Hope this
> will work with patch collection and updating individual transform.
>
> Nicolas
>
> > On 26 Nov 2016, at 15:53, Joshua Klein <mobiusklein at gmail.com> wrote:
> >
> > I’ve had great success using PathPatch and AffineTransform for this
> purpose:
> >
> > from matplotlib import pyplot as
> >  plt
> >
> > from matplotlib.path import
> >  Path
> >
> > from matplotlib.transforms import
> >  Affine2D
> >
> > from matplotlib.patches import
> >  PathPatch
> >
> > unit_triangle = Path.unit_regular_polygon(
> > 3
> > )
> >
> >
> > def make_triangle(x, y, rot_deg, color, scale):
> >
> >     path = Path(unit_triangle.vertices * scale, unit_triangle.codes)
> >     trans = Affine2D().translate(x, y).rotate_deg_around(x, y, rot_deg)
> >     t_path = path.transformed(trans)
> >     patch = PathPatch(t_path, facecolor=color)
> >
> > return
> >  patch
> >
> > ax = plt.gca()
> >
> >
> > for x, y, rot_deg in [(1, 1, 90), (2, 2, 45), (-1, 1, 128
> > )]:
> >     patch = make_triangle(x, y, rot_deg,
> > "blue", 1
> > )
> >
> >
> > # Patches don't automatically change the visible range of the axes like
> scatter does.
> >
> > ax.autoscale()
> >
> >
> > On Sat, Nov 26, 2016 at 9:21 AM, Nicolas P. Rougier <
> Nicolas.Rougier at inria.fr> wrote:
> >
> > I would like to draw several triangles (same size, same color) with
> different individual orientations.
> > Scatter plot does not allow to specify individual orientations and I've
> a hard time with PatchCollection.
> >
> > What would be the easiest way ? Is there an example somewhere around by
> any chance ?
> >
> >
> > Nicolas
> > _______________________________________________
> > Matplotlib-users mailing list
> > Matplotlib-users at python.org
> > https://mail.python.org/mailman/listinfo/matplotlib-users
> >
>
>
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```