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@@ -0,0 +1,119 @@
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+#############################################################################
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+# Copyright (c) 2013 by Panagiotis Mavrogiorgos
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+# All rights reserved.
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+#
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+# Redistribution and use in source and binary forms, with or without
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+# modification, are permitted provided that the following conditions are met:
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+#
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+# * Redistributions of source code must retain the above copyright notice,
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+# this list of conditions and the following disclaimer.
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+# * Redistributions in binary form must reproduce the above copyright notice,
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+# this list of conditions and the following disclaimer in the documentation
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+# and/or other materials provided with the distribution.
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+# * Neither the name(s) of the copyright holders nor the names of its
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+# contributors may be used to endorse or promote products derived from this
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+# software without specific prior written permission.
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+#
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+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AS IS AND ANY EXPRESS OR
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+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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+# MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
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+# EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
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+# OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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+# LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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+# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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+# EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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+#############################################################################
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+#
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+# @license: http://opensource.org/licenses/BSD-3-Clause
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+
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+from bisect import bisect_left
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+import logging
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+
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+log = logging.getLogger('base')
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+
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+
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+class BilinearInterpolation(object):
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+ """
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+ Bilinear interpolation with optional extrapolation.
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+ Usage:
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+ table = BilinearInterpolation(
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+ x_index=(1, 2, 3),
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+ y_index=(1, 2, 3),
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+ values=((110, 120, 130),
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+ (210, 220, 230),
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+ (310, 320, 330)),
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+ extrapolate=True)
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+
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+ assert table(1, 1) == 110
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+ assert table(2.5, 2.5) == 275
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+
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+ """
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+ def __init__(self, x_index, y_index, values):
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+ # sanity check
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+ x_length = len(x_index)
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+ y_length = len(y_index)
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+
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+ if x_length < 2 or y_length < 2:
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+ raise ValueError("Table must be at least 2x2.")
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+ if y_length != len(values):
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+ raise ValueError("Table must have equal number of rows to y_index.")
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+ if any(x2 - x1 <= 0 for x1, x2 in zip(x_index, x_index[1:])):
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+ raise ValueError("x_index must be in strictly ascending order!")
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+ if any(y2 - y1 <= 0 for y1, y2 in zip(y_index, y_index[1:])):
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+ raise ValueError("y_index must be in strictly ascending order!")
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+
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+ self.x_index = x_index
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+ self.y_index = y_index
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+ self.values = values
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+ self.x_length = x_length
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+ self.y_length = y_length
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+ self.extrapolate = True
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+
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+ #slopes = self.slopes = []
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+ #for j in range(y_length):
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+ #intervals = zip(x_index, x_index[1:], values[j], values[j][1:])
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+ #slopes.append([(y2 - y1) / (x2 - x1) for x1, x2, y1, y2 in intervals])
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+
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+ def __call__(self, x, y):
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+ # local lookups
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+ x_index, y_index, values = self.x_index, self.y_index, self.values
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+
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+ i = bisect_left(x_index, x) - 1
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+ j = bisect_left(y_index, y) - 1
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+
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+ if self.extrapolate:
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+ # fix x index
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+ if i == -1:
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+ x_slice = slice(None, 2)
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+ elif i == self.x_length - 1:
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+ x_slice = slice(-2, None)
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+ else:
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+ x_slice = slice(i, i + 2)
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+
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+ # fix y index
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+ if j == -1:
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+ j = 0
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+ y_slice = slice(None, 2)
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+ elif j == self.y_length - 1:
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+ j = -2
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+ y_slice = slice(-2, None)
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+ else:
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+ y_slice = slice(j, j + 2)
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+ else:
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+ if i == -1 or i == self.x_length - 1:
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+ raise ValueError("Extrapolation not allowed!")
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+ if j == -1 or j == self.y_length - 1:
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+ raise ValueError("Extrapolation not allowed!")
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+
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+ # if the extrapolations is False this will fail
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+ x1, x2 = x_index[x_slice]
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+ y1, y2 = y_index[y_slice]
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+ z11, z12 = values[j][x_slice]
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+ z21, z22 = values[j + 1][x_slice]
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+
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+ return (z11 * (x2 - x) * (y2 - y) +
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+ z21 * (x - x1) * (y2 - y) +
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+ z12 * (x2 - x) * (y - y1) +
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+ z22 * (x - x1) * (y - y1)) / ((x2 - x1) * (y2 - y1))
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Marius Stanciu