interpolate.py

import numpy as np
from scipy.stats import norm


def lerp(val, low, high):
    """Linear interpolation"""
    return low + (high - low) * val


def lerp_gaussian(val, low, high):
    """Linear interpolation with gaussian CDF"""
    low_gau = norm.cdf(low)
    high_gau = norm.cdf(high)
    lerped_gau = lerp(val, low_gau, high_gau)
    return norm.ppf(lerped_gau)


def slerp(val, low, high):
    """Spherical interpolation. val has a range of 0 to 1."""
    if val <= 0:
        return low
    elif val >= 1:
        return high
    elif np.allclose(low, high):
        return low
    omega = np.arccos(np.dot(low/np.linalg.norm(low), high/np.linalg.norm(high)))
    so = np.sin(omega)
    return np.sin((1.0-val)*omega) / so * low + np.sin(val*omega)/so * high


def slerp_gaussian(val, low, high):
    """Spherical interpolation with gaussian CDF (generally not useful)"""
    offset = norm.cdf(np.zeros_like(low))  # offset is just [0.5, 0.5, ...]
    low_gau_shifted = norm.cdf(low) - offset
    high_gau_shifted = norm.cdf(high) - offset
    circle_lerped_gau = slerp(val, low_gau_shifted, high_gau_shifted)
    epsilon = 0.001
    clipped_sum = np.clip(circle_lerped_gau + offset, epsilon, 1.0 - epsilon)
    result = norm.ppf(clipped_sum)
    return result


def get_interpfn(spherical, gaussian):
    """Returns an interpolation function"""
    if spherical and gaussian:
        return slerp_gaussian
    elif spherical:
        return slerp
    elif gaussian:
        return lerp_gaussian
    else:
        return lerp