Sonar-Based Localization

I am currently using four SRF05 Ultrasonic Range Finder for obstacle avoidance on my Quadrotor. I would like to know is it possible to use this 4 ultrasonic range finder to do mapping/localizing in an indoor environment? Has anyone tried/done this before?

Sounds interesting. I'm thinking about it but have not got time to try yet. Since your 4 sonic rangers are pointing into 4 directions, you can estimate with a fitting curve. Say if all 4 are facing forward in a row, then you can fit the distance of all 4 of their readings for an overall profile in front of the coptor. If one of then can scan its angle with a motor, then you can slowly map the whole surrounding.

When in doubt, google it out.