'Set the projection type.
Parameters
proj_type : str
Type of projection, accepts \'persp\' and \'ortho\'.'

def set_proj_type(self, proj_type):

    if (proj_type == u'persp'):
        self._projection = proj3d.persp_transformation
    elif (proj_type == u'ortho'):
        self._projection = proj3d.ortho_transformation
    else:
        raise ValueError((u'unrecognized    projection:    %s' % proj_type))
