Novel view render

[yf1019]

Hi sidan, A very nice work. Here is a question about the code of rendering a 360 degree of the human. I'm very interested about it but I could not understand it. Could anyone share me how does this code work?

https://github.com/zju3dv/animatable_nerf/blob/5cb948815007a590b49b5611a710b0fb14cf4c79/lib/utils/render_utils.py#L61

def gen_path(RT, center=None): lower_row = np.array([[0., 0., 0., 1.]])

# transfer RT to camera_to_world matrix
RT = np.array(RT)
RT[:] = np.linalg.inv(RT[:])

RT = np.concatenate([RT[:, :, 1:2], RT[:, :, 0:1],
                     -RT[:, :, 2:3], RT[:, :, 3:4]], 2)

up = normalize(RT[:, :3, 0].sum(0))  # average up vector
z = normalize(RT[0, :3, 2])
vec1 = normalize(np.cross(z, up))
vec2 = normalize(np.cross(up, vec1))
z_off = 0

if center is None:
    center = RT[:, :3, 3].mean(0)
    z_off = 1.3

c2w = np.stack([up, vec1, vec2, center], 1)

# get radii for spiral path
tt = ptstocam(RT[:, :3, 3], c2w).T
rads = np.percentile(np.abs(tt), 80, -1)
rads = rads * 1.3
rads = np.array(list(rads) + [1.])

render_w2c = []
for theta in np.linspace(0., 2 * np.pi, cfg.render_views + 1)[:-1]:
    # camera position
    cam_pos = np.array([0, np.sin(theta), np.cos(theta), 1] * rads)
    cam_pos_world = np.dot(c2w[:3, :4], cam_pos)
    # z axis
    z = normalize(cam_pos_world -
                  np.dot(c2w[:3, :4], np.array([z_off, 0, 0, 1.])))
    # vector -> 3x4 matrix (camera_to_world)
    mat = viewmatrix(z, up, cam_pos_world)

    mat = np.concatenate([mat[:, 1:2], mat[:, 0:1],
                          -mat[:, 2:3], mat[:, 3:4]], 1)
    mat = np.concatenate([mat, lower_row], 0)
    mat = np.linalg.inv(mat)
    render_w2c.append(mat)

return render_w2c

[pengsida]

https://github.com/zju3dv/neuralbody/issues/88