My tools of the trade for python programming.
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# $Id: spline_2d.py,v 1.1 2010-01-22 18:48:19 wirawan Exp $
#
# wpylib.math.spline_2d module
# Created: 20091204
# Wirawan Purwanto
#
import numpy
import scipy.interpolate
class spline_2d:
"""Simple interpolation for two-dimensional curve.
Created to handle the quirks of current SciPy interpolation
routines."""
# Important notes on spline CAVEATS:
# - for some reason we HAVE to make a copy of the 'x' array
# (to make it contiguous, probably?)
# - also, the x values better be sorted in ascending order, or else
# the routine would return nonsense (i.e. NaN's).
def __init__(self, x, y):
self.init(x,y)
def init(self, x, y):
# First, the x must be sorted, so we make a private copy of
# the data:
self.data = numpy.array(zip(x, y), dtype=[('x', float), ('y', float)])
# Quirk 1: The x axis data must be sorted ascending
self.data.sort(order=['x'])
self.x = self.data['x']
self.y = self.data['y']
# Quirk 2: the x data for spline function must be contiguous
# See below in init_spline_params()
#self.x_copy = self.x.copy()
try:
del self.spline_params
except:
pass
def init_spline_params(self):
"""Initialize spline params with default params.
You can call something to initialize the spline params before
calling the first spline function if you want different, non-default
parameters."""
self.spline_params \
= scipy.interpolate.splrep(self.x, self.y, s=0)
def spline(self, xnew):
try:
params = self.spline_params
except:
self.init_spline_params()
return scipy.interpolate.splev(x=xnew, tck=self.spline_params, der=0)
class spline_2d_piecewise:
"""Simple spline_2d interpolator with piecewise datasets.
Interpolation is possible only in the ranges defined by the piecewise
datasets.
No checking is done whether the pieces are overlapping, discontinuous, etc.
The first piece found enclosing the coordinate will be taken for
interpolation."""
def __init__(self, *datasets):
self.init(*datasets)
def init(self, *datasets):
#if len(dsets) % 2:
# raise ValueError, "The input datasets must be given in x, y pairs
self.pieces = []
for dset in datasets:
x = dset[0]
y = dset[1]
xmin = numpy.min(x)
xmax = numpy.max(x)
piece = spline_2d(x, y)
piece.xmin = xmin
piece.xmax = xmax
self.pieces.append(piece)
def in_range(self, piece, x):
return piece.xmin <= x and x <= piece.xmax
def get_piece(self, x):
for p in self.pieces:
if self.in_range(p, x):
return p
raise ValueError, "Out-of-range x value = %g" % x
def spline(self, x):
return self.get_piece(x).spline(x)