How to meshgrid this non-rectangular shape (a trapezoid) – to be used for 3d volumteric visualtion – python

Question

Im trying to create a volume with a custom shape, to add Z-axis data I need to mesh X-Y data.
Hence my issue. I’d like to have this shape as the base
Trapezoid Base

However, after doing

X,Y = np.mesh(x,y)

I get a symmetric rectangle rather than the trapezoid-looking like shape.
meshed data

is there another effecient way I can fill the trapezoid ?

here is the code:

    x1 = np.zeros(20)
    y1 = np.linspace(-2,2,20)

    x2 = np.linspace(0,30,20)
    y2 = np.sqrt((   5/max(x2) * x2 +4     ))

    x3 = np.linspace(0, 30, 20)
    y3 = -np.sqrt((5 / max(x3) * x3 + 4))

    x4 = np.ones(20)*30
    y4 = np.linspace(-3,3,20)

    x = np.concatenate((x1, x2, x3, x4))
    y = np.concatenate((y1,y2,y3,y4))

    # u,v = np.meshgrid(x,y)
    # x = u.flatten()
    # y = v.flatten()

    plt.plot(x,y)
    plt.show()

Trying to fill a trapizoid shape to construct a 3d volume representation using plotly

Asked By: Hady Farrag

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Source

Answer 1

I think you can do something like this.

The key is to define a normalized version of y that has a domain of -1 to 1 and multiply it by your final equation for y

import numpy as np
import matplotlib.pyplot as plt

n = 20
x = np.linspace(0, 30, n)
y = np.linspace(-1, 1, n)

xx, yy = np.meshgrid(x, y)

yy *= np.sqrt(5/x.max() * x + 4)

plt.scatter(xx, yy)
plt.show()

Answered By: Roy Smart

How to meshgrid this non-rectangular shape (a trapezoid) – to be used for 3d volumteric visualtion – python

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