plot interpolated surface in python

Question

I have a 4x4 matrix (test4x4) which I want to interpolate it to a 8x8 matrix (test8x8). I used interpolate.interp2d for interpolation, but when I plot it (test8x8), it does not seem like test4x4 plot. Where do I mistake?

import numpy as np
from scipy import interpolate
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D

mymin,mymax = 0,3
X = np.linspace(mymin,mymax,4)
Y = np.linspace(mymin,mymax,4)

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

test4x4 = np.array([[ 1.2514318 ,  1.25145821,  1.25148472,  1.25151133],
   [ 1.25087456,  1.25090105,  1.25092764,  1.25095435],
   [ 1.25031581,  1.25034238,  1.25036907,  1.25039586],
   [ 1.24975557,  1.24978222,  1.24980898,  1.24983587]])

f = interpolate.interp2d(x,y,test4x4,kind='cubic')

# use linspace so your new range also goes from 0 to 3, with 8 intervals
Xnew = np.linspace(mymin,mymax,8)
Ynew = np.linspace(mymin,mymax,8)

test8x8 = f(Xnew,Ynew)

print('test8x8=',test8x8)

plot1=plt.figure(1)
plt.title('test 4X4')
fig1 = plt.figure(1)
ax1 = fig1.gca(projection='3d')
ax1.plot_surface(x.T,y.T, test4x4, alpha = 1, rstride=1, cstride=1, linewidth=0.5, antialiased=True, zorder = 0.5)
plt.xlabel('x')
plt.ylabel('y')
plt.grid()

ax1.plot_surface(Xnew.T, Ynew.T, test8x8, alpha = 1, rstride=1, cstride=1, linewidth=0.5, antialiased=True, zorder = 0.5)
plt.grid()

plt.show()

I think I could solve this problem, I should use x1,y1 = np.meshgrid(Xnew,Ynew).

swatchai · Accepted Answer · 2020-08-03 14:20:42Z

1

For 8x8, you also need a meshgrid:

...
Xnew = np.linspace(mymin,mymax,8)
Ynew = np.linspace(mymin,mymax,8)
xx, yy = np.meshgrid(Xnew, Ynew)  #You need this

And use this meshgrid to plot

ax1.plot_surface(xx.T, yy.T, test8x8, alpha=0.5, rstride=1, cstride=1, \
                   linewidth=0.5, antialiased=True, zorder = 10)

Use alpha=0.5 in both plot_surface(), so that, you can see both surfaces.

To separate the 2 surfaces more distinctly, you can try the second .plot_surface() as

ax1.plot_surface(xx.T, yy.T, 0.0001+test8x8, alpha=0.5, rstride=1, cstride=1, \
                   linewidth=0.5, antialiased=True, zorder = 10)

The value 0.0001 brings the second surface higher (in z-direction).

edited Aug 3, 2020 at 14:20

answered Aug 3, 2020 at 13:26

swatchai

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