Read the root node from an acclaim skeleton file stream.

def read_root(self, fid):
        """Read the root node from an acclaim skeleton file stream."""
        lin = self.read_line(fid)                    
        while lin[0] != ':':
            parts = lin.split()
            if parts[0]=='order':
                order = []
                for i in range(1, len(parts)):
                    if parts[i].lower()=='rx':
                        chan = 'Xrotation'
                        order.append('x')
                    elif parts[i].lower()=='ry':
                        chan = 'Yrotation'
                        order.append('y')
                    elif parts[i].lower()=='rz':
                        chan = 'Zrotation'
                        order.append('z')
                    elif parts[i].lower()=='tx':
                        chan = 'Xposition'
                    elif parts[i].lower()=='ty':
                        chan = 'Yposition'
                    elif parts[i].lower()=='tz':
                        chan = 'Zposition'
                    elif parts[i].lower()=='l':
                        chan = 'length'
                    self.vertices[0].meta['channels'].append(chan)
                    # order is reversed compared to bvh
                self.vertices[0].meta['order'] = order[::-1]

            elif parts[0]=='axis':
                # order is reversed compared to bvh
                self.vertices[0].meta['axis_order'] = parts[1][::-1].lower()
            elif parts[0]=='position':
                self.vertices[0].meta['offset'] = [float(parts[1]),
                                       float(parts[2]),
                                       float(parts[3])]
            elif parts[0]=='orientation':
                self.vertices[0].meta['orientation'] =  [float(parts[1]),
                                             float(parts[2]),
                                             float(parts[3])]
            lin = self.read_line(fid)
        return lin