How big is the park? And what sort of accuracy are you after? What equipment do you have available and/or what sort ofd budget are you hoping to keep within? F

How big is the park? And what sort of accuracy are you after? What equipment do you have available and/or what sort ofd budget are you hoping to keep within? For an "on the cheap, lots of DIY" approach - I've got an inexpensive (~$40 from memory) laser rangefinder with sub cm accuracy and a range of a bit over 100m (it'll get ~120m for things with "good" reflective properties, sometimes only 50m or so for "bad" surfaces). If the park is a suitable size, you could probably start with a Google Satellite view, and measure enough distances to triangulate everything to calibrate the satellite imagery. I've considered (but never gotten around to) attaching a 3 axis digital compass module so I can record angles and elevations for each distance measurement. That'd help a lot of there are lots of objects you want to plot positions for - you wouldn't need 2-3 measurements from different known locations for each object that way. See also my other comment about using a drone and photogrammetry.