sdf file for a visual tag

I need a tag to land a quadcopter in Gazebo. I created the tag (.dae) using Blender, but now I have to make the model (.sdf) and I can't figure how exactly. The tag is 9cm x 9cm x 5mm The tag will be only a paper pasted on the floor, so mass=0. Is this OK? What do I have to put in uri? 0 0 0 0 0 0true1.00.00.00.00.00.00.00.09 0.09 0.0050.09 0.09 0.0051 1 1package://i_dont/know/what/do_i_have/to_put_here.dae Having only the .sdf file is ok or do I need something more? What? Is it better to put the model in .gazebo/models or in another folder and then link it (how?) Thanks