def project_to_2d_purelinear(X):
    """
    Project 3D points to 2D using only linear parameters .

    Arguments:
    X -- 3D points in *camera space* to transform (N, *, 3)
    """
    assert X.shape[-1] == 3

    # XX = torch.clamp(X[..., :2] / X[..., 2:], min=-1, max=1)
    XX = X[..., :2] / X[..., 2:]

    # f is the scale that related to the absolute depth information.
    f = 2.3

    return XX * f