5 Best Ways to Check if a Point Lies on or Inside a Rectangle in Python

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💡 Problem Formulation: Determining the position of a point relative to a rectangle is a common computational geometry problem. In Python, developers often need to check whether a given point (x, y) lies within the bounds of a rectangle defined by its corners or sides. The desired outcome is a boolean answer – True if the point is on or within the rectangle, otherwise False.

Method 1: Comparing Coordinates

The first method involves comparing the coordinates of the point with the coordinates of the rectangle. A point (x, y) lies inside or on the boundary of a rectangle if it satisfies the inequalities xmin ≤ x ≤ xmax and ymin ≤ y ≤ ymax, where (xmin, ymin) and (xmax, ymax) define the rectangle.

Here’s an example:

def is_inside_rectangle(point, rect):
    x, y = point
    xmin, ymin, xmax, ymax = rect
    return xmin <= x <= xmax and ymin <= y <= ymax

# Rectangle coordinates (xmin, ymin, xmax, ymax)
rectangle = (1, 1, 10, 10)
# Point coordinates (x, y)
point = (5, 5)
print(is_inside_rectangle(point, rectangle))

Output: True

This method directly compares the point’s x and y coordinates to the boundaries of the rectangle to determine inclusion. The function returns True if the point is on or inside the rectangle, and False otherwise.

Method 2: Using Shapely Library

The Shapely library provides geometric objects, predicates, and operations in Python. To use it for our problem, we create a Point object and a Polygon object representing the rectangle and use the contains method to check if the rectangle contains the point.

Here’s an example:

from shapely.geometry import Point, Polygon

def is_inside_rectangle_shapely(point, rect):
    return Polygon(rect).contains(Point(point))

rectangle = [(1, 1), (1, 10), (10, 10), (10, 1)]
point = (5, 5)
print(is_inside_rectangle_shapely(point, rectangle))

Output: True

The Shapely library simplifies the process by handling geometric computations internally. It’s a robust and simple solution for geometric problems, but it requires installing the external Shapely package.

Method 3: Ray Casting Algorithm

The Ray Casting algorithm checks how many times a horizontal line starting from the point intersects with the sides of the rectangle. For a simple rectangle aligned with the axes, this method simply becomes another form of coordinate comparison.

Here’s an example:

def is_inside_rectangle_ray_casting(point, rect):
    x, y = point
    xmin, ymin, xmax, ymax = rect
    return xmin <= x <= xmax and ymin <= y <= ymax

rectangle = (1, 1, 10, 10)
point = (5, 5)
print(is_inside_rectangle_ray_casting(point, rectangle))

Output: True

This method applied to an axis-aligned rectangle is virtually identical to the first method. In more complex geometrical contexts, ray casting can be adapted for arbitrary polygons—not just rectangles—and can account for point-inclusion even with non-rectilinear borders.

Method 4: Use of Complex Numbers

In this method, we treat coordinates as complex numbers. By verifying all the complex numbers (corners of the rectangle) relative to the point, we can determine if the point lies within or on the rectangle.

Here’s an example:

def is_inside_rectangle_complex(point, rect):
    z = complex(*point)
    z1, z2, z3, z4 = map(lambda co: complex(*co), rect)
    return z1.real <= z.real <= z3.real and z1.imag <= z.imag <= z3.imag

rectangle = [(1, 1), (1, 10), (10, 10), (10, 1)]
point = (5, 5)
print(is_inside_rectangle_complex(point, rectangle))

Output: True

This method offers an elegant and less conventional approach to a common problem. While not necessary for rectangles aligned with the axes, it can be appealing for those comfortable with complex numbers and can be extended to other polygon checks.

Bonus One-Liner Method 5: Using Lambda Function

The fifth method makes use of a lambda function to check if the point is inside the rectangle, providing a very concise version of the coordinate comparison method.

Here’s an example:

is_inside_rectangle_lambda = lambda p, r: r[0] <= p[0] <= r[2] and r[1] <= p[1] <= r[3]

rectangle = (1, 1, 10, 10)
point = (5, 5)
print(is_inside_rectangle_lambda(point, rectangle))

Output: True

This one-liner approach is succinct and compact. The lambda function is suitable for simple, one-off checks without the need for reuse or readability concerns. However, for complex cases and readability, it is advisable to use named functions.

Summary/Discussion

  • Method 1: Comparing Coordinates. Simple and direct method. Weakness: Not suitable for rotated rectangles or complex polygons.
  • Method 2: Using Shapely Library. Robust and easy. Weakness: Requires external library installation.
  • Method 3: Ray Casting Algorithm. Good for non-axis aligned polygons. Weakness: Overly complex for simple rectangles.
  • Method 4: Use of Complex Numbers. Elegant and versatile. Weakness: Unnecessary for axis-aligned rectangles; more suited to those familiar with complex numbers.
  • Bonus Method 5: Lambda Function. Compact and quick. Weakness: Not very readable for complex conditions or reuse.