Situm is constantly checking whether the user is following the route and, otherwise, computes a new route or instructions.

• User goes out of route

At any moment, an user may go out the route that she is following. For instance, she might continue through a corridor when she should take a left. 

Situm detects these situations and recomputes the new route automatically. Sometimes, the route will be the same as before (therefore, Situm will inform the user to turn around and proceed with the previous route). Other times, the old route will no longer be the shortest one, and a new optimal route will be computed.  

The following figure shows an example of such situations. The user location & orientation is represented by the blue arrow   and the destination is the "Shop 4" . The user is following the shortest route (left), but for some reason, she turns around and starts walking in an opposite direction (left). After a while, a new shortest route is recomputed (right).

• User direction is contrary to the route direction advance

A special case of re-routing is when the user is not heading in the advance direction of the route. For instance, she might be heading on the opposite direction. In this case, Situm will not recompute the whole route but only the instructions: this user will be told to "Turn around" to continue with the route.

This is what happens in the previous figure (center). More details in the Turn-by-turn indications Section