So for a project of mine, I would like to build a robot that can use an ultrasonic sensor to detect a stand-alone object in a path, and successfully navigate around said object while traveling in the same direction. In other words, the robot should move forward, recognize an object in the path using an ultrasonic sensor, travel around the object and resume going in a straight line.
The robot would just have to keep track of how far from the path it had deviated and then go around the object until it was back to the path. Fairly simple 2D trig and math. Going around the object is a lot like following a wall.
I think it depends how accurately you want to achieve this (how accurately do you need it to resume the original course) and how flexible you want it to be (what would happen if it encountered another obstacle during this detour?). If you only want a rough answer, you could probably get close enough with dead reckoning i.e. assume that the robot does exactly what you ask it to do and simply pre-program a sequence of corners and straight lines to feel its way past the obstacle.
In reality the robot will not always turn by exactly the amount you specified or travel exactly the right distance, so to get more accurate answers you need to give the robot a way to detect where it is and which way it is facing. Which is possible, but a lot more work.