How to get accurate Ground Control Point with trimble Sitewo…
i’m not in (building)construction, so the accuracy at ‘cm level’ is pretty much good enough for my jobs (roads, urban designs). However, in urban environment with highrise and other sky-obstructions like trees GPS just won’t cut it near buildings.
On a job i had this week i placed 2 GCPs and set up my totalstation. Vertical error was about 2.5cm on the totalstation. Nothing i am bothered about, but right after setup the controlpoints were allready off by those 2.5cm. To be fair, X/Y was a bit more important on this job than Z, i took this error for granted since it taken so long for the GCPs to make.
HOWEVER. To answer the above questions, it’s hard to reference… without an reference. All i have are these 2 GCPs i made in sub optimal conditions. To get more feeling about the measurements and info it gives me i perhaps should make some sort of test setup with know references (like a level board with 2 nails and measuring them seeing if they are off in Z-height), i kinda trust the hardware to much…
So, i checked my software and i can’t find any settings related to measurement times or the maximum amount of points it gets. On my old topcon set it indeed took about 3 seconds/measurements before the point is stored, on my Trimble set it kinda gets more accurate the longer you stand still.
Which results in me kinda constantly walking and takeing measurements in open fields, and standing still for a couple of seconds when i need a more detailed measurement. When i press the measure button (+ icon on screen or the <enter> button on the keyboard) it instantly records the point.
Posted by: @absurveyor18548
however, if you need mm accurate vertical control id just hold one benchmark and run a level through the…
Indeed, i always make a reference point ‘the guys’ use for height reference and that they need to check with a laser if they want to be sure. GPS isn’t accurate enough for some cases…
Posted by: @absurveyor18548
Make sure you go into the settings of whatever type of shot you are taking (topo or observed control point I assume, I use Trimble access so I’m not sure if siteworks has the same.)
Trimble access is pretty much a whole different kind of software layout. Saw it on a co-workers setup, looks nothing alike :(. i also don’t use most of the features it has, but it came with the device.. so fml i guess :P.
Posted by: @absurveyor18548
Make sure to change your observation time and number of measurements to something higher.
Other than time and/or wanted accuracy i don’t see any other options. And setting the wanted accuracy to high kinda makes it run indefinitly because it doesn’t reach it (unless you stop it yourself). On my topcon set i could let it run for 15 minutes and in time the ‘visual accuracy on screen’ got better over time, never worse.
Posted by: @mightymoe
I have to say our Trimble units with Access are measuring well within the 8mm + 1PPM that they are rated (RTK). This is after many, many, many cross checks.
Many, many, many cross checks. Seems like a time consuming action. I guess when i would be in an open field i probably get this without any problem too :’).
Posted by: @mightymoe
Measure them with GPS, then see how they check using a tape and level, you will find out quickly if those numbers displayed on the screen mean anything or are bull**ht.
Good practice i guess. It’s nice to have ‘state of the art’ hardware, but if whatever it outputs is just some random number it doesn’t mean anything i guess.
Never met any realworld problems *knocks on wood* with (extremely) false measurements. Did have an ‘incident’ recently where my GPS was 10cm off in the Z-direction. Good thing i had some controlpoints to check, otherwise some (not so important) building would have been 10cm too high…
The next day the error was gone, but it made my doubt my hardware for a couple of hours :(.
dont mind my ‘to’ or ‘too’ mixups, not a native english speaker.
This post was modified 7 months ago by
This post was modified 7 months ago by OMEGA-ThundeR
