OK here is how to proceed, works fine for me:
I use the annotation system to route /locations/nearby/{latitude}/{longitude}
/**
* Return a nearby location
* @Get("/locations/nearby/{latitude}/{longitude}", requirements={"latitude" = "[-+]?(\d*[.])?\d+", "longitude" = "[-+]?(\d*[.])?\d+"})
*/
public function nearbyAction($latitude, $longitude) {...}
Then I have to specify float numbers with: requirements={"latitude" = "[-+]?(\d*[.])?\d+", "longitude" = "[-+]?(\d*[.])?\d+"}
Those will still be interpreted as string by the controller: "64.1333", I just have to use this in the controller:
floatval($latitude)
to get url parameters as float and then do my calculations!