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Non-Maximum Suppression (NMS)

Implement Non-Maximum Suppression (NMS) for 2D point detections.

Given a list of detections, each represented as $[x, y, score]$ , and a distance threshold $d$ , suppress detections that are within distance $d$ of a higher-scoring detection.

Algorithm:

Sort detections by score in descending order
Initialize an empty list of kept detections
For each detection (in score order):
- If it is within Euclidean distance $d$ of any already-kept detection, suppress it (skip)
- Otherwise, keep it

The Euclidean distance between two points $(x_1, y_1)$ and $(x_2, y_2)$ is: $d = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}$

Return the surviving detections sorted by score in descending order. Each detection should be returned as $[x, y, score]$ with values rounded to 4 decimal places.

Example:

Input:

detections = [[10, 10, 0.9], [12, 12, 0.8], [50, 50, 0.7], [11, 11, 0.6]]
dist_threshold = 5.0

Output:

[[10, 10, 0.9], [50, 50, 0.7]]

Reasoning:

First, sort the detections by score in descending order: $[[10, 10, 0.9], [12, 12, 0.8], [50, 50, 0.7], [11, 11, 0.6]]$
Then, iterate through the sorted detections and apply NMS:
- The detection $[10, 10, 0.9]$ is kept as it's the first one.
- The detection $[12, 12, 0.8]$ is within distance $d = 5.0$ of $[10, 10, 0.9]$ since $d = \sqrt{(12 - 10)^2 + (12 - 10)^2} = \sqrt{8} \approx 2.83 < 5.0$ , so it's suppressed.
- The detection $[11, 11, 0.6]$ is also within distance $d = 5.0$ of $[10, 10, 0.9]$ since $d = \sqrt{(11 - 10)^2 + (11 - 10)^2} = \sqrt{2} \approx 1.41 < 5.0$ , so it's suppressed.
- The detection $[50, 50, 0.7]$ is kept as it's not within distance $d = 5.0$ of any already kept detection.
The final output is the kept detections sorted by score in descending order: $[[10, 10, 0.9], [50, 50, 0.7]]$

Constraints:

detections: List of [x, y, score]
dist_threshold: float (distance threshold for suppression)
Return: List of surviving detections sorted by score descending
Round values to 4 decimal places
Use pure Python + math

Editor

Python 3.13.1

Test Results

0/0

Run code to see test results.

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