From 47e657aaa33a08388ba1d5060734aad359726919 Mon Sep 17 00:00:00 2001
From: Matthias Bisping <matthias.bisping@axbit.com>
Date: Wed, 4 Jan 2023 12:04:57 +0100
Subject: [PATCH] Refactoring

Clean up and prove correctness of intersection computation
---
 cv_analysis/utils/spacial.py    | 41 +++++++++++++++++++++++++++++++++
 cv_analysis/utils/structures.py | 16 +++++--------
 2 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/cv_analysis/utils/spacial.py b/cv_analysis/utils/spacial.py
index 9504c2a..863ada0 100644
--- a/cv_analysis/utils/spacial.py
+++ b/cv_analysis/utils/spacial.py
@@ -1,6 +1,7 @@
 # See https://stackoverflow.com/a/39757388/3578468
 from __future__ import annotations
 
+from operator import attrgetter
 from typing import TYPE_CHECKING, Iterable
 
 from funcy import juxt, rpartial
@@ -109,3 +110,43 @@ def is_contained(rectangle: Rectangle, rectangles: Iterable[Rectangle]):
     """Check if the rectangle is contained within any of the other rectangles."""
     other_rectangles = filter(lambda r: r != rectangle, rectangles)
     return any(map(rpartial(contains, rectangle), other_rectangles))
+
+
+def intersection(alpha, beta):
+    return intersection_along_x_axis(alpha, beta) * intersection_along_y_axis(alpha, beta)
+
+
+def intersection_along_x_axis(alpha, beta):
+    return intersection_along_axis(alpha, beta, "x")
+
+
+def intersection_along_y_axis(alpha, beta):
+    return intersection_along_axis(alpha, beta, "y")
+
+
+def intersection_along_axis(alpha, beta, axis):
+    assert axis in ["x", "y"]
+
+    def get_component_accessor(component):
+        return attrgetter(f"{axis}{component}")
+
+    c1 = get_component_accessor(1)
+    c2 = get_component_accessor(2)
+
+    # Cases:
+    #    a      b
+    # [-----] (---)  => [a1, b1, a2, b2] => max(0, (a2 - b1)) = 0
+    #   b      a
+    # (---) [-----]  => [b1, a1, b2, a2] => max(0, (b2 - a1)) = 0
+    #     a   b
+    # [--(----]----) => [a1, b1, a2, b2] => max(0, (a2 - b1)) = (a2 - b1)
+    #     a b
+    # (-[---]----)   => [b1, a1, a2, b2] => max(0, (a2 - a1)) = (a2 - a1)
+    #     b a
+    # [-(---)----]   => [a1, b1, b2, a2] => max(0, (b2 - b1)) = (b2 - b1)
+    #     b   a
+    # (----[--)----] => [b1, a1, b2, a2] => max(0, (b2 - a1)) = (b2 - a1)
+
+    coords = [*sorted([c1(alpha), c1(beta)]), *sorted([c2(alpha), c2(beta)])]
+    intersection = max(0, coords[2] - coords[1])
+    return intersection
diff --git a/cv_analysis/utils/structures.py b/cv_analysis/utils/structures.py
index dd3223b..89fdaa0 100644
--- a/cv_analysis/utils/structures.py
+++ b/cv_analysis/utils/structures.py
@@ -4,7 +4,7 @@ from typing import Iterable
 import numpy as np
 from funcy import identity
 
-from cv_analysis.utils.spacial import adjacent, contains
+from cv_analysis.utils.spacial import adjacent, contains, intersection
 
 
 class Rectangle:
@@ -52,19 +52,15 @@ class Rectangle:
     def xywh(self):
         return self.x1, self.y1, self.w, self.h
 
-    def intersection(self, rect):
-        bx1, by1, bx2, by2 = rect.xyxy()
-        if (self.x1 > bx2) or (bx1 > self.x2) or (self.y1 > by2) or (by1 > self.y2):
-            return 0
-        intersection_ = (min(self.x2, bx2) - max(self.x1, bx1)) * (min(self.y2, by2) - max(self.y1, by1))
-        return intersection_
+    def intersection(self, other):
+        return intersection(self, other)
 
     def area(self):
         return (self.x2 - self.x1) * (self.y2 - self.y1)
 
-    def iou(self, rect):
-        intersection = self.intersection(rect)
-        union = self.area() + rect.area() - intersection
+    def iou(self, other):
+        intersection = self.intersection(other)
+        union = self.area() + other.area() - intersection
         return intersection / union
 
     def includes(self, other: "Rectangle", tol=3):