How to extract x and y coordinates from LIDAR sensor(LMS511) dat

ghz 昨天 ⋅ 5 views

How to extract x and y coordinates from LIDAR sensor(LMS511) data in Python?

I have a LIDAR sensor, specifically the SICK LMS511, which outputs continuous data in the following format:

sRA LMDscandata 0 1 151FDC8 0 0 EC4B EDD5 85BF655E 85BF9621 0 0 3E 0 0 2710 21C 0 1 DIST1 3F800000 00000000 4A0E5 1A0B B5 305 30F 312 315 320 325 328 32F 0 0 B62 B35 B16 AD8 AC9 742 753 767 779 791 7A8 7B8 764 782 793 7B1 7C8 7E5 7FF 817 807 806 834 824 816 802 7F8 7E8 7DA 7C9 7B0 7AF 797 789 780 771 767 781 7AB 7A6 796 788 77F 77E 771 76B 769 751 74A 742 73A 732 731 724 71C 71C 716 70F 707 701 701 6FC 6F2 6F2 6E9 6EC 6E7 6E5 6E3 6E4 6DA 6D6 6D5 6D5 6D6 6D4 6D8 6D7 6D2 6CE 6D2 6D4 6D4 6D4 6CE 6D0 6D8 6E3 6DC 6E1 6E4 6E4 6E9 6E9 6FA 6ED 6F7 6F7 702 70A 707 712 710 71A 720 726 728 730 73C 740 74A 751 759 765 76D 770 787 78A 796 7A3 7A9 7B2 7C6 7D5 7E2 7E9 7FC 808 809 828 837 848 85B 86B 87B 88C 89B 8B3 8D1 8E8 8F8 90F 91C 93E 957 971 989 96A 94E 974 992 9B9 9CC 9E5 A11 A88 AD7 B09 B2F B59 B8A BB5 BE8 C1E C54 C85 CBD D07 D3A D81 DC6 0 0 0 0 0 0

I want to extract the x and y coordinates from this data. How can I do this in Python?

Note: Please note that this is just one sample data from the sensor, and it outputs continuous data in this format.

I have tried to extract the x and y coordinates from the LIDAR data using Python. Specifically, I attempted to parse the data using Python and extract the coordinates. However, I have not been successful in extracting the coordinates.

Answer

To extract the x and y coordinates from the LIDAR sensor data, we need to first understand the format of the data. From your example, it looks like the sensor is returning a series of distance measurements that are encoded in a hexadecimal format. You’ll likely need to interpret these hexadecimal values as distances (and possibly angles), then convert them to Cartesian coordinates (x, y).

Here's a step-by-step guide on how you can approach this:

1. Understand the Data Structure

Looking at the raw data, you can see that it includes several distance measurements in hexadecimal format. From the sensor's documentation, you might find that these measurements correspond to distances along different angles. For each distance, you’ll need to know the corresponding angle to convert the polar coordinates (distance, angle) into Cartesian coordinates (x, y).

2. Breaking Down the Data

  • DIST1, DIST2, DIST3, etc., might correspond to different distance measurements at different angles.
  • The data appears to be a continuous stream with each group representing a distance measurement.

3. Conversion of Hexadecimal Data

Each of the DIST values like 3F800000, 00000000, etc., might represent a distance. These values are likely stored as floats or integers in hexadecimal format.

You'll need to:

  1. Convert these hexadecimal values to integers or floats.
  2. Compute the x and y coordinates using the distance and angle.

4. Steps to Extract x, y Coordinates:

Here’s a Python script that demonstrates how you can process this data and extract the x and y coordinates.

import struct
import math

# Sample LIDAR data (a shortened example for demonstration purposes)
lidar_data = "sRA LMDscandata 0 1 151FDC8 0 0 EC4B EDD5 85BF655E 85BF9621 0 0 3E 0 0 2710 21C 0 1 DIST1 3F800000 00000000 4A0E5 1A0B B5 305 30F 312 315 320 325 328 32F 0 0 B62 B35 B16 AD8 AC9 742 753 767 779 791 7A8 7B8 764 782 793 7B1 7C8 7E5 7FF 817 807 806 834 824 816 802 7F8 7E8 7DA 7C9 7B0 7AF 797 789 780 771 767 781 7AB 7A6 796 788 77F 77E 771 76B 769 751 74A 742 73A 732 731 724 71C 71C 716 70F 707 701 701 6FC 6F2 6F2 6E9 6EC 6E7 6E5 6E3 6E4 6DA 6D6 6D5 6D5 6D6 6D4 6D8 6D7 6D2 6CE 6D2 6D4 6D4 6D4 6CE 6D0 6D8 6E3 6DC 6E1 6E4 6E4 6E9 6E9 6FA 6ED 6F7 6F7 702 70A 707 712 710 71A 720 726 728 730 73C 740 74A 751 759 765 76D 770 787 78A 796 7A3 7A9 7B2 7C6 7D5 7E2 7E9 7FC 808 809 828 837 848 85B 86B 87B 88C 89B 8B3 8D1 8E8 8F8 90F 91C 93E 957 971 989 96A 94E 974 992 9B9 9CC 9E5 A11 A88 AD7 B09 B2F B59 B8A BB5 BE8 C1E C54 C85 CBD D07 D3A D81 DC6 0 0 0 0 0 0"

# Function to parse the LIDAR data
def parse_lidar_data(data):
    # Split the data string into parts
    parts = data.split()

    # Find the index where the distance data starts (assuming DIST1 is at index 15)
    dist_index = parts.index("DIST1") + 1

    # Extract the distance values (in hexadecimal) and convert to float (assuming IEEE 754 format)
    distances = []
    for i in range(dist_index, len(parts), 2):  # Assuming the format for each distance is two hex digits
        hex_value = parts[i]
        if len(hex_value) == 8:  # IEEE 754 float32
            # Convert hex string to a 32-bit float
            float_value = struct.unpack('!f', bytes.fromhex(hex_value))[0]
            distances.append(float_value)

    return distances

# Function to convert polar (distance, angle) to Cartesian (x, y)
def polar_to_cartesian(distances, angle_increment=1.0):
    coordinates = []
    for i, dist in enumerate(distances):
        angle = math.radians(i * angle_increment)  # Convert angle to radians
        x = dist * math.cos(angle)
        y = dist * math.sin(angle)
        coordinates.append((x, y))
    return coordinates

# Parse the LIDAR data
distances = parse_lidar_data(lidar_data)

# Convert distances to Cartesian coordinates
coordinates = polar_to_cartesian(distances)

# Print out the coordinates
for i, (x, y) in enumerate(coordinates):
    print(f"Point {i+1}: x={x:.2f}, y={y:.2f}")

Explanation:

  1. Parsing the LIDAR Data:

    • The parse_lidar_data() function splits the raw data string into a list of values.
    • It looks for DIST1 as the start of the distance data and then converts the subsequent hexadecimal values into floats using struct.unpack().

  2. Converting Polar to Cartesian:

    • The polar_to_cartesian() function takes the distances and assumes an angle increment of 1 degree (this is a simplification—you might need the exact angle steps from your LIDAR configuration).
    • It then converts each distance/angle pair to Cartesian coordinates using the standard polar-to-Cartesian conversion:
      • x = distance * cos(angle)
      • y = distance * sin(angle)

  3. Printing the Coordinates:

    • The coordinates are printed in the form (x, y) for each point.

Notes:

  • Angle Increment: The angle between consecutive distance measurements (i.e., the resolution of the LIDAR scanner) is typically a fixed value, but you should refer to your sensor's documentation to get the exact value. For example, if your sensor is scanning in 360 degrees and produces 360 distance readings, the angle increment would be 1 degree. If it produces 720 readings, the angle increment would be 0.5 degrees.

  • Data Format: Ensure the LIDAR data is being transmitted as expected, especially the hexadecimal format. If your sensor uses a different encoding or data format (e.g., 16-bit integers instead of 32-bit floats), you’ll need to adjust the code accordingly.

  • Error Handling: The example assumes a simple structure for the data, but in real-world usage, you might want to add error handling to account for malformed or incomplete data.

This code should give you a good starting point for extracting x and y coordinates from the LIDAR sensor’s output. You can adjust the data parsing part as necessary, depending on the exact format of your sensor's data.

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