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| -rw-r--r-- | fg21sim/utils/interpolate.py | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/fg21sim/utils/interpolate.py b/fg21sim/utils/interpolate.py new file mode 100644 index 0000000..a129723 --- /dev/null +++ b/fg21sim/utils/interpolate.py @@ -0,0 +1,42 @@ +# Copyright (c) 2017 Weitian LI <weitian@aaronly.me> +# MIT license + +""" +Interpolation utilities. +""" + + +def bilinear(x, y, p11, p12, p21, p22): + """ + Interpolate (x,y) from values associated with four points. + + The four points are a list of four triplets: (x, y, value). + The four points can be in any order. They should form a rectangle. + + p11 --+-- p12 + | | | + +--(x,y)--+ + | | | + p21 --+-- p22 + + Credit + ------ + [1] http://en.wikipedia.org/wiki/Bilinear_interpolation + [2] https://stackoverflow.com/a/8662355/4856091 + """ + # Sort points by X then Y + points = sorted([p11, p12, p21, p22]) + x1, y1, q11 = points[0] + _x1, y2, q12 = points[1] + x2, _y1, q21 = points[2] + _x2, _y2, q22 = points[3] + + if x1 != _x1 or x2 != _x2 or y1 != _y1 or y2 != _y2: + raise ValueError("points do not form a rectangle") + if not x1 <= x <= x2 or not y1 <= y <= y2: + raise ValueError("(x, y) not within the rectangle") + a1 = (q11 * (x2 - x) * (y2 - y) + q21 * (x - x1) * (y2 - y) + + q12 * (x2 - x) * (y - y1) + q22 * (x - x1) * (y - y1)) + a2 = (x2 - x1) * (y2 - y1) + q = a1 / a2 + return q |