Only problem is it seems you need a gps aswell if dealing with other people's sites
You don't neeeed GPS. GPS sounds lovely but it has its issues with close proximity buildings, trees etc blocking the satellites. On smaller projects, you can assign your own co-ordinates off an existing building or features and go from there. Its only relative to what you tell it. If you were setting out HS2 then maybe GPS would be useful. But if you were building the new runway at Heathrow for example, you have plenty to go off that's existing so wouldn't need it there really.
Often you would be following a topo survey that would set up control points anyway so if setting out you go off these. Beware though - I had piles set out using GPS once, then we tried to set out edge of shutter for the ground beam once they were installed and the whole site turned out to be 300mm in the wrong longitude! Bloody control point had the wrong number against it and it gave our total station the wrong info - therefore putting our work in the wrong position. Took a couple of hours to work out where the issue was and we got there in the end by checking our selves against the existing man road. But my point is, don't always trust the topo survey!
I had this again more recently when a manhole in the road was given the wrong level. I used it as my datum thinking it wouldn't move throughout the project and had to dig the entire plot 140mm more than I originally thought because it transpired the number given on the drawing for the manhole level was wrong!
Put it this way... I always double check now....
GPS would have solved both these issues but it also creates others. Its good but not 100% yet in my opinion and all engineers who run GPS will have a traditional total station in the boot of the truck as a backup.
Pics of the job in Chaldon where I had the 300mm issue. I will never forget the lesson learnt that day. Was pretty pleased with the outcome though. This was back in 2014 before every groundworker on linked in was trying to show how tidy their work was. Wouldn't cut it today - Id have to have rainbow barriers around the plot and spray every drain telling everyone its a foul drain! But back then I like to think we were ahead of the curve.