Triggertrap Mobile is a step up from most iOS DSLR triggers. Besides being able to control your DSLR’s feature set from your phone, it also includes a distance-lapse mode and a eased timelapse mode. The distance-lapse mode triggers your camera’s shutter based your phone’s GPS coordinates (e.g. every 30 feet) while the eased timelapse mode can make timelapses accelerate over time. Of course, this requires an app as well as a dongle, but both those will only run you $3o total.