local function main()
    local st = display.getCurrentStage()
    local g = display.newGroup()
    local re = display.newRect(g, 0, 0, 100, 50)
    re:setReferencePoint( display.TopLeftReferencePoint )
    re.x = 0; re.y = 0
    g.x = 100 ;g.y = 100 ;

    local objs = {} ; g.objs = objs
    local function create( id )
        local id = id
        local constx = 100/6
        local consty = 50*0.5
        local result = {}
        if id == 2 then id = 3
        elseif id == 3 then id = 5 end
        result.center = {x = constx*id, y = consty}
        return result
    end
    for i =1 , 3 do -- create 3 virtual obj in g, it just a center point in g coordination.
        objs[i] = create(i)
    end
    local function setref( id )
        g.xReference = objs[id].center.x
        g.yReference = objs[id].center.y
    end
    setref(1);g.x = 100 ;g.y = 100 ;
    g.rotation = 0
    --print( g:localToContent(g.objs[1].center.x, g.objs[1].center.y))
    g.rotation = 60 -- after rotation
    --print( g:localToContent(g.objs[1].center.x, g.objs[1].center.y)) -- this line make bug
                                       -- if remove comment
    setref(2);g.x = 100 ;g.y = 100 ;

    local point = display.newCircle(0, 0, 5); point:setReferencePoint( display.CenterReferencePoint )
    point.x = 100; point.y = 100
    point:setFillColor(225, 0, 0)
end
main()