def _gather_low_dim_input(self, obs):
        '''
            Concatenate (along 2nd dimension) all the low-dimensional
            (propioceptive) features from input observation tuple
            Args:
                obs: dictionary of tensors
        '''
        if 'low_dim' not in obs.keys(): return None
        list_obs_ld = [obs['low_dim'][key] for key in obs['low_dim'].keys()]
        obs_low_dim = torch.cat(list_obs_ld, -1)
        return obs_low_dim

            Concatenate (along 2nd dimension) all the low-dimensional
            (propioceptive) features from input observation tuple
            Args:
                obs: dictionary of tensors
        
surreal/model/ppo_net.py