restraing_2_2d.py

import matplotlib.pyplot as plt
import numpy as np


def lidar_to_2d_front_view(points,
                           v_res,
                           h_res,
                           v_fov,
                           val="depth",
                           cmap="jet",
                           saveto=None,
                           y_fudge=0.0
                           ):
    """ Takes points in 3D space from LIDAR data and projects them to a 2D
        "front view" image, and saves that image.

    Args:
        points: (np array)
            The numpy array containing the lidar points.
            The shape should be Nx4
            - Where N is the number of points, and
            - each point is specified by 4 values (x, y, z, reflectance)
        v_res: (float)
            vertical resolution of the lidar sensor used.
        h_res: (float)
            horizontal resolution of the lidar sensor used.
        v_fov: (tuple of two floats)
            (minimum_negative_angle, max_positive_angle)
        val: (str)
            What value to use to encode the points that get plotted.
            One of {"depth", "height", "reflectance"}
        cmap: (str)
            Color map to use to color code the `val` values.
            NOTE: Must be a value accepted by matplotlib's scatter function
            Examples: "jet", "gray"
        saveto: (str or None)
            If a string is provided, it saves the image as this filename.
            If None, then it just shows the image.
        y_fudge: (float)
            A hacky fudge factor to use if the theoretical calculations of
            vertical range do not match the actual data.

            For a Velodyne HDL 64E, set this value to 5.
    """

    # DUMMY PROOFING
    assert len(v_fov) == 2, "v_fov must be list/tuple of length 2"
    assert v_fov[0] <= 0, "first element in v_fov must be 0 or negative"
    assert val in {"depth", "height", "reflectance"}, \
        'val must be one of {"depth", "height", "reflectance"}'

    x_lidar = points[:, 0]
    y_lidar = points[:, 1]
    z_lidar = points[:, 2]
    r_lidar = points[:, 3]  # Reflectance
    # Distance relative to origin when looked from top
    d_lidar = np.sqrt(x_lidar ** 2 + y_lidar ** 2)
    # Absolute distance relative to origin
    # d_lidar = np.sqrt(x_lidar ** 2 + y_lidar ** 2, z_lidar ** 2)

    v_fov_total = -v_fov[0] + v_fov[1]

    # Convert to Radians
    v_res_rad = v_res * (np.pi / 180)
    h_res_rad = h_res * (np.pi / 180)

    # PROJECT INTO IMAGE COORDINATES
    x_img = np.arctan2(-y_lidar, x_lidar) / h_res_rad
    y_img = np.arctan2(z_lidar, d_lidar) / v_res_rad

    # SHIFT COORDINATES TO MAKE 0,0 THE MINIMUM
    x_min = -360.0 / h_res / 2  # Theoretical min x value based on sensor specs
    x_img -= x_min  # Shift
    x_max = 360.0 / h_res  # Theoretical max x value after shifting

    y_min = v_fov[0] / v_res  # theoretical min y value based on sensor specs
    y_img -= y_min  # Shift
    y_max = v_fov_total / v_res  # Theoretical max x value after shifting

    y_max += y_fudge  # Fudge factor if the calculations based on
    # spec sheet do not match the range of
    # angles collected by in the data.

    # WHAT DATA TO USE TO ENCODE THE VALUE FOR EACH PIXEL
    if val == "reflectance":
        pixel_values = r_lidar
    elif val == "height":
        pixel_values = z_lidar
    else:
        pixel_values = -d_lidar

    # PLOT THE IMAGE
    cmap = "jet"  # Color map to use
    dpi = 100  # Image resolution
    fig, ax = plt.subplots(figsize=(x_max / dpi, y_max / dpi), dpi=dpi)
    ax.scatter(x_img, y_img, s=1, c=pixel_values, linewidths=0, alpha=1, cmap=cmap)
    ax.set_facecolor((0, 0, 0))  # Set regions with no points to black
    ax.axis('scaled')  # {equal, scaled}
    ax.xaxis.set_visible(False)  # Do not draw axis tick marks
    ax.yaxis.set_visible(False)  # Do not draw axis tick marks
    plt.xlim([0, x_max])  # prevent drawing empty space outside of horizontal FOV
    plt.ylim([0, y_max])  # prevent drawing empty space outside of vertical FOV

    if saveto is not None:
        fig.savefig(saveto, dpi=dpi, bbox_inches='tight', pad_inches=0.0)
    else:
        fig.show()


if __name__ == "__main__":
    lidar = np.fromfile('./data/000000.bin', dtype=np.float32, count=-1).reshape([-1, 4])

    HRES = 0.35  # horizontal resolution (assuming 20Hz setting)
    VRES = 0.4  # vertical res
    VFOV = (-24.9, 2.0)  # Field of view (-ve, +ve) along vertical axis
    Y_FUDGE = 5  # y fudge factor for velodyne HDL 64E

    lidar_to_2d_front_view(lidar, v_res=VRES, h_res=HRES, v_fov=VFOV, val="depth",
                           saveto="./tmp/lidar_depth.png", y_fudge=Y_FUDGE)

    lidar_to_2d_front_view(lidar, v_res=VRES, h_res=HRES, v_fov=VFOV, val="height",
                           saveto="./tmp/lidar_height.png", y_fudge=Y_FUDGE)

    lidar_to_2d_front_view(lidar, v_res=VRES, h_res=HRES, v_fov=VFOV,
                           val="reflectance", saveto="./tmp/lidar_reflectance.png",
                           y_fudge=Y_FUDGE)