Source code for pybtls.utils.IL_compress

__all__ = ["compress_discrete_IL"]




def compress_discrete_IL(x: list[float], y: list[float], e: float) -> tuple[list, list]:
    """
    Compresses a set of discrete points (x, y) \n
    by removing points that are within a certain error tolerance e of a line
    connecting the start point to a trial point. \n
    Returns the compressed set of points as two separate lists.

    Parameters
    ----------
    x : list[float]\n
        List of x-coordinates of the points.\n
    y : list[float]\n
        List of y-coordinates of the points.\n
    e : float\n
        Maximum relative error allowed for a point to be considered part of the line.

    Returns
    -------
    tuple[list, list]\n
        A tuple containing two lists: the compressed x-coordinates and the compressed y-coordinates.
    """

    n = len(x)
    xs = [x[0]]
    ys = [y[0]]
    k1 = 0  # Index of the starting point

    for k in range(1, n):
        m = (y[k] - y[k1]) / (
            x[k] - x[k1]
        )  # Slope of line from start point to trial point
        emax = 0
        max_j = k1

        for j in range(k1 + 1, k + 1):  # Include point k in the check as well
            yline = m * (x[j] - x[k1]) + y[k1]

            # Calculate relative error
            if y[j] == 0:
                etrial = abs(yline)
            else:
                etrial = abs((yline - y[j]) / y[j])

            if etrial > emax:
                emax = etrial
                max_j = j  # Store the index where max error occurred

        if emax > e:
            xs.append(x[max_j])
            ys.append(y[max_j])
            k1 = max_j  # Update starting point

    xs.append(x[-1])  # Add the last point
    ys.append(y[-1])

    return xs, ys