How do I model a LiDAR with arbitrary scan pattern?

edit

I would like to model a lidar system with an arbitrary scan pattern. What I have in mind in particular is a kind of irregular raster pattern. I am aware of the block laser scanner, which scans on a regular grid in angle space. What I'd like to do is read in a list of arbitrary angular coordinates and perform ranging at those angles. I would of course like to accomplish this with minimal modifications to the existing ROS/Gazebo code base. Somewhere there must be a for loop that iterates over a regular grid of angular coordinates. Instead I'd like to read in an array of arbitrary coordinates and loop over those. I have gone into the Gazebo source code, but feel like I'm going down a rabbit hole. I would appreciate some expert advice.