Ground truth map for a gazebo world like the willowgarage model

Hi all, I use the turtlebot in the willowgarage world to create a semantic mapping system. As the actual mapping (using gmapping for example) is not the most important part of this effort, I would like to be able to use ground truths for the start as well. I found a way to get the ground truth pose (using the topic /gazebo/model_states), but now I also want a way to get the ground truth map, or at least some way to construct such a map. Is that possible? Alternatively, is there a way to provide gmapping with the ground truth pose such that it just builds perfect maps (assuming a static world)? Ultimately I would like to have a tf frame /mobile_base_groudntruth and a map topic /map_groundtruth. Any help is very much appreciated! Best, Koen