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Geometry

get_polygon_center

Calculate the center of a polygon. The center is calculated as the center of the solid figure formed by the points of the polygon

Parameters:

Name Type Description Default

polygon ΒΆ

 ndarray

A 2-dimensional numpy ndarray representing the vertices of the polygon.

 required

Returns:

Name Type Description
Point Point

The center of the polygon, represented as a Point object with x and y attributes.

Raises:

Type Description
ValueError

If the polygon has no vertices.

Examples:

import numpy as np
import supervision as sv

polygon = np.array([[0, 0], [0, 2], [2, 2], [2, 0]])
sv.get_polygon_center(polygon=polygon)
# Point(x=1, y=1)
Source code in supervision/geometry/utils.py 
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def get_polygon_center(polygon: np.ndarray) -> Point:
    """
    Calculate the center of a polygon. The center is calculated as the center
    of the solid figure formed by the points of the polygon

    Parameters:
        polygon (np.ndarray): A 2-dimensional numpy ndarray representing the
            vertices of the polygon.

    Returns:
        Point: The center of the polygon, represented as a
            Point object with x and y attributes.

    Raises:
        ValueError: If the polygon has no vertices.

    Examples:
        ```python
        import numpy as np
        import supervision as sv

        polygon = np.array([[0, 0], [0, 2], [2, 2], [2, 0]])
        sv.get_polygon_center(polygon=polygon)
        # Point(x=1, y=1)
        ```
    """

    # This is one of the 3 candidate algorithms considered for centroid calculation.
    # For a more detailed discussion, see PR #1084 and commit eb33176

    if len(polygon) == 0:
        raise ValueError("Polygon must have at least one vertex.")

    shift_polygon = np.roll(polygon, -1, axis=0)
    signed_areas = np.cross(polygon, shift_polygon) / 2
    if signed_areas.sum() == 0:
        center = np.mean(polygon, axis=0).round()
        return Point(x=center[0], y=center[1])
    centroids = (polygon + shift_polygon) / 3.0
    center = np.average(centroids, axis=0, weights=signed_areas).round()

    return Point(x=center[0], y=center[1])

Position

Bases: Enum

Enum representing the position of an anchor point.

Source code in supervision/geometry/core.py 
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class Position(Enum):
    """
    Enum representing the position of an anchor point.
    """

    CENTER = "CENTER"
    CENTER_LEFT = "CENTER_LEFT"
    CENTER_RIGHT = "CENTER_RIGHT"
    TOP_CENTER = "TOP_CENTER"
    TOP_LEFT = "TOP_LEFT"
    TOP_RIGHT = "TOP_RIGHT"
    BOTTOM_LEFT = "BOTTOM_LEFT"
    BOTTOM_CENTER = "BOTTOM_CENTER"
    BOTTOM_RIGHT = "BOTTOM_RIGHT"
    CENTER_OF_MASS = "CENTER_OF_MASS"

    @classmethod
    def list(cls):
        return list(map(lambda c: c.value, cls))

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