Why use depth_map,z_vals in rendering.py,not the distance map, distance

[haowang020110]

Thanks to your work at first!
I'm confused that in rendering.py,
z_vals were sampled from near distance and far distance, and the xyz_coarse_sampled = rays_o.unsqueeze(1) + rays_d.unsqueeze(1) * z_vals.unsqueeze(2) # (N_rays, N_samples, 3) also proves that z_val is distance not depth.