:param D: network depth :param W: network width :param input_ch: input channels for encodings of (x, y, z) :param input_ch_viewdirs: input channels for encodings of view directions :param skips: skip connection in network :param use_viewdirs: if True,
(self, D=8, W=256, input_ch=3, input_ch_viewdirs=3,
skips=[4], use_viewdirs=False)
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