CODEWITHSUNDEEP
pythonpoint-cloudslidar
Hadar Shavit
Hadar Shavit

Reputation: 149

Python graph segmentation

I am trying to detect an open door using LIDAR. I have 270 degrees LIDAR read and I'm trying to detect the door from the graph:

enter image description here

The door is the peak between 100 and 150. enter image description here

The door is between ~30 and ~40.

enter image description here

Here there is a "noise" spike.

I can see that there is a huge spike in the graph where the door "starts" and "ends". I wondered if the is a scipy/numpy or other library function that can detect this.

Thanks

Upvotes: 1

Views: 361

Answers (2)

eandklahn
eandklahn

Reputation: 577

Looking at data like this, it is somewhat noisy for a peak-finding algorithm, but I suggest playing around with the following procedure, where the peak finding is done on a smoothed version of the dataset.

import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import find_peaks
from scipy.ndimage import gaussian_filter

D = np.load('lidar.npy')
D2 = gaussian_filter(D, sigma=3)
A = find_peaks(D2, width=5, prominence=4, distance=10)

As you can see, I'm first using your dataset lidar.npy, and the found peaks are plotted using

for a in A[0]:
    plt.axvline(a)
plt.plot(D2)
plt.show()

which marks one peak like this.

lidar.npy

For the other dataset, using the same parameters, the procedure gives

lidar_d.npy

Upvotes: 1

user11718531
user11718531

Reputation:

I don't think there is a function for this, your problem is kind of specific. But, I think it wouldn't be hard to detect this manually, since other parts of the detection don't have such high derivatives.

You can do something like this:

dx = 2
dy = 4

spike_start = None
spike_end = None

for i in range(len(points)):
    # Detect high derivative when spike starts
    if spike_start is None and points[i] - points[i-dx] >= dy:
        spike_start = i

    # Detect high negative derivative when spike ends
    if spike_start is not None and points[i-dx] - points[i] >= dy:
        spike_end = i
        break

if spike_start is not None and spike_end is not None:
    print(f"Door is between {spike_start} and {spike_end}")
else:
    print("Door not found")

Play with dx and dy to properly detect the spike.

Upvotes: 1

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