How to get Gazebo walking actor able to do path planning?

Hi, I am trying to build a gazebo environment, in which a walking person actor needs to do path planning in the given world. I have two questions: 1. I modified corridor.world and use it as the basic world, with walls around. With the [code example](http://gazebosim.org/tutorials?tut=actor&cat=build_robo), I use the same obstacle handler function. But the actor just goes through the wall. I checked that each wall is a collision model, and the ignore_obstacles in the actor part doesn't include those wall models. I am very confused why the actor doesn't consider wall as an obstacle. 2. What should I do if I want to make the actor do path planning in the given world? I didn't find the api that can get the occupancy map, and here is the world [document](http://osrf-distributions.s3.amazonaws.com/gazebo/api/dev/classgazebo_1_1physics_1_1World.html). I am fairly new to gazebo and I will appreciate if you can shed some light on this. Thanks in advance.