[SciPy-User] Problems evaluating interpolated function at new points
Matteo Niccoli
matteo at mycarta.ca
Thu May 14 17:15:27 EDT 2015
I am relatively new to Scipy, at least when it comes to interpolation. I
am trying to replicate some of the functionality of Matlab's interp2.
I have a distance function map (available at this Google drive location)
https://drive.google.com/open?id=0B6acq_amk5e3X0Q5UG1ya1VhSlE&authuser=0
Values are normalized in the range 0-1. Size is 200 rows by 300 columns.
I can load it up with this code snippet:
import numpy as np
dstnc1=np.load('dstnc.npy')
Coordinates are defined by the next snippet:
xmin = 0.
xmax = 9000.
ymin = 0.
ymax = 6000.
r1,c1 = dstnc1.shape
x = np.linspace(xmin,xmax,c1)
y = np.linspace(ymin, ymax,r1)
I have three map points defined by vectors xnew1, ynew1 with this snippet:
xnew1=[3700.540199,3845.940199,3983.240199]
ynew1=[1782.8611,1769.862,1694.862]
I check their location with respect to the distance map with this:
import matplotlib.pyplot as plt
fig = plt.figure(figsize=(20, 16))
ax = fig.add_subplot(1, 1, 1)
plt.imshow(dstnc1, cmap=my_cmap_r,vmin=0,vmax=0.3,
extent=[0, 9000, 0, 6000], origin='upper')
plt.scatter(xnew1, ynew1, s=50, linewidths=0.15)
plt.show()
They plot in the correct location. Now I would like to extract the
distance value at those three points. I tried first interp2d.
from scipy.interpolate import interp2d
x1 = np.linspace(xmin,xmax,c1)
y1 = np.linspace(ymin,ymax,r1)
f = interp2d(x1, y1, dstnc1, kind='cubic')
but when I try to evaluate with:
test=f(xnew,ynew)
I get this error message:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-299-d0f42e609b23> in <module>()
----> 1 test=f(xnew,ynew)
C:\...\AppData\Local\Continuum\Anaconda\lib\site-packages\scipy\interpolate\interpolate.pyc
in __call__(self, x, y, dx, dy)
270 (self.y_min, self.y_max)))
271
--> 272 z = fitpack.bisplev(x, y, self.tck, dx, dy)
273 z = atleast_2d(z)
274 z = transpose(z)
C:\...\AppData\Local\Continuum\Anaconda\lib\site-packages\scipy\interpolate\fitpack.pyc
in bisplev(x, y, tck, dx, dy)
1027 z,ier = _fitpack._bispev(tx,ty,c,kx,ky,x,y,dx,dy)
1028 if ier == 10:
-> 1029 raise ValueError("Invalid input data")
1030 if ier:
1031 raise TypeError("An error occurred")
ValueError: Invalid input data
If I try RectBivariateSpline:
from scipy.interpolate import RectBivariateSpline
x2 = np.linspace(xmin,xmax,r1)
y2 = np.linspace(ymin,ymax,c1)
f = RectBivariateSpline(x2, y2, dstnc1)
I get this error:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-302-d0f42e609b23> in <module>()
----> 1 test=f(xnew,ynew)
C:\...\AppData\Local\Continuum\Anaconda\lib\site-packages\scipy\interpolate\fitpack2.pyc
in __call__(self, x, y, mth, dx, dy, grid)
643 z,ier = dfitpack.bispev(tx,ty,c,kx,ky,x,y)
644 if not ier == 0:
--> 645 raise ValueError("Error code returned by
bispev: %s" % ier)
646 else:
647 # standard Numpy broadcasting
ValueError: Error code returned by bispev: 10
Any suggestion as to whether I am using the wrong functions or the right
function with wrong syntax, and how I may fix it is appreciated. Thank you
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