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BODY_PARTS_KPT_IDS = [[1, 2], [1, 5], [2, 3], [3, 4], [5, 6], [6, 7], [1, 8], [8, 9], [9, 10], [1, 11],
                      [11, 12], [12, 13], [1, 0], [0, 14], [14, 16], [0, 15], [15, 17], [2, 16], [5, 17]]
BODY_PARTS_PAF_IDS = ([12, 13], [20, 21], [14, 15], [16, 17], [22, 23], [24, 25], [0, 1], [2, 3], [4, 5],
                      [6, 7], [8, 9], [10, 11], [28, 29], [30, 31], [34, 35], [32, 33], [36, 37], [18, 19], [26, 27])

Both BODY_PARTS_KPT_IDS and BODY_PARTS_PAF_IDS are related to the start and end keypoints of a limb, but they serve slightly different purposes in the context of pose estimation.

1. BODY_PARTS_KPT_IDS

• This array explicitly defines the start and end keypoints for each limb or body part.
• Each sub-array [a, b] represents a connection (or limb) between two keypoints:
  • a: The index of the starting keypoint.
  • b: The index of the ending keypoint.
• Example:
  • [1, 2]: Represents the connection between keypoint 1 (neck) and keypoint 2 (right shoulder).
  • [2, 3]: Represents the connection between keypoint 2 (right shoulder) and keypoint 3 (right elbow).
• Purpose:
  • Used to group detected keypoints into meaningful body parts (e.g., limbs).
  • Helps in identifying which keypoints are connected to form a limb.

2. BODY_PARTS_PAF_IDS

• This array defines the PAF (Part Affinity Field) indices that correspond to the connections (or limbs) between keypoints.
• Each tuple (x, y) represents the indices of the PAF channels in the PAF map that correspond to a specific limb:
  • x: The PAF channel for the x-direction of the connection.
  • y: The PAF channel for the y-direction of the connection.
• Example:
  • [12, 13]: Represents the PAF channels for the connection between keypoint 1 (neck) and keypoint 2 (right shoulder).
  • [14, 15]: Represents the PAF channels for the connection between keypoint 2 (right shoulder) and keypoint 3 (right elbow).
• Purpose:
  • Used to evaluate the strength and direction of connections between detected keypoints.
  • Helps in determining whether two keypoints are connected based on the PAF values.

Relationship Between the Two Arrays

• BODY_PARTS_KPT_IDS defines which keypoints are connected to form a body part (e.g., a limb).
• BODY_PARTS_PAF_IDS defines which PAF channels correspond to the connection between those keypoints.