Medium

Cast a Lidar Fan

~20 mincode completion

Implement lidar_scan(origin, angles, obstacles, max_range). origin is [x, y], angles are ray headings in radians (direction ), and obstacles is an array of rows . Return one distance per angle.

Examples

Straight at a circle: the reading is the near surface, 4 not 5

Input
lidar_scan([0, 0], [0], [[5, 0, 1]], 10)
Output
[4]

Nothing that way: the ray reads max_range

Input
lidar_scan([0, 0], [1.5707963267948966], [[5, 0, 1]], 10)
Output
[10]

A four-ray fan around one obstacle

Input
lidar_scan([0, 0], [0, 1.5707963267948966, 3.141592653589793, 4.71238898038469], [[5, 0, 1]], 10)
Output
[4, 10, 10, 10]

Hints

Hint 1

Use a matrix product rather than nested loops, and check which operand transposes.

Hint 2

A common slip here: returned the distance to the circle centre instead of to its surface.

Requirements

  • origin: [x, y] start of every ray

  • angles: (K,) ray headings in radians

  • obstacles: (N, 3) rows [cx, cy, radius]

  • max_range: reading returned when a ray hits nothing

  • Return (K,) distances, each in (0, max_range]

Constraints

  • Allowed library: NumPy only

  • Time limit: 200 ms, Memory: 64 MB

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Python
import numpy as np


def lidar_scan(origin, angles, obstacles, max_range):
    """
    Distance to the nearest circular obstacle along each ray.

    Args:
        origin:    [x, y] start of every ray
        angles:    (K,) ray headings in radians
        obstacles: (N, 3) rows [cx, cy, radius]
        max_range: reading returned when a ray hits nothing

    Returns:
        (K,) distances, each in (0, max_range]
    """
    # YOUR CODE HERE
    pass
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