From 9929159a769e0575ff8654b840b4090c4495a8de Mon Sep 17 00:00:00 2001
From: Aaron LI <aly@aaronly.me>
Date: Mon, 31 Jul 2017 21:55:33 +0800
Subject: utils: Add interpolate.py with "bilinear()" function
Signed-off-by: Aaron LI <aly@aaronly.me>
---
fg21sim/utils/interpolate.py | 42 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 42 insertions(+)
create mode 100644 fg21sim/utils/interpolate.py
(limited to 'fg21sim/utils')
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
--
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