rend_util.py

def ray_sphere_intersection_rough(
    rays_o: torch.Tensor, rays_d: torch.Tensor, *,
    r=1.0, keepdim=True, t_min_cons: float=0.0, t_max_cons: float=None) -> Tuple[torch.Tensor, torch.Tensor]:
    """
    NOTE: Modified from https://github.com/Totoro97/NeuS
    rays_o: camera center's coordinate
    rays_d: camera rays' directions. already normalized.
    """
    dir_scale = rays_d.norm(dim=-1, keepdim=keepdim).clamp_min_(1e-10)
    # NOTE: (minus) the length of the line projected from [the line from camera to sphere center] to [the line of camera rays]
    #       scale: In the scaled space.
    mid = -torch.sum(rays_o * rays_d / dir_scale, dim=-1, keepdim=keepdim)
    # NOTE: a convservative approximation of the half chord length from ray intersections with the sphere.
    #       all half chord length < r
    #       scale: In the original un-scaled space.
    near, far = ((mid - r)/dir_scale).clamp_min_(t_min_cons), ((mid + r)/dir_scale).clamp_(r/dir_scale, t_max_cons)
    return near, far

mid = -torch.sum(rays_o * rays_d / dir_scale.unsqueeze(-1), dim=-1, keepdim=keepdim)