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Topcon MM GPS Curb and Gutter

FNG Member

Anyone here run with a company using Topcon MM GPS for their curb and gutter operations? 

If so, when they set their mm control points do they run a level loop through them for vertical? Do you use a level typically or a total station if you level loop?

Also how do you typically deal with the tie in's on the job? Do you just shoot the tie ins and inlets and ignore the hubs once you're a few hundred feet from the tie in?


Topic starter Posted : April 28, 2020 2:01 pm
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VA LS 2867
200+ posts Member

All control points for MM are established with a level or total station from project control or utilize a MM base on a control point to set out where another point is needed.

 Tie-ins are located early to ensure the model matches in to existing conditions.  I typically stop the model about 50 short if in tangent, or 25' in curve so that we make sure the tie in points work as designed.  

Posted : April 28, 2020 2:45 pm
1,000+ posts Member

Vertical control for mmGPS needs to be within a "gnats a$$". If you can do that with your TS, great! We prefer using a digital level.

Posted : April 29, 2020 3:04 am

FNG Member

Have you guys ever ran a level loop with a total station? 

I've never done it but am looking into it.

Our process before was to set mm hubs using GPS. Then once the surveyor set his hubs we would setup our total station, resect it in off the mm points we shot with GPS. And then go and check the surveyors hubs in the center of the job. 

However far off we were from their hubs somewhere in the center of the job we would adjust our range pole height to match. Then reshoot our mm hubs off the adjusted range pole height to put them on the same plane.

I think this process we had was incorrect which is why I'm working to fix it. Our vertical is off cause of not running a level (at all) through our mm from the same benchmark that was used by the surveyors to stake the walk/curb. 

We would have issues matching the surveyors hubs which are gospel to the inspector.

I know our process was bad and makes no sense lol

Any links you have to running a level loop with a total station? 

Topic starter Posted : April 29, 2020 10:05 am
500+ posts Member


There are situations where trig levelling makes sense, particularly in steep terrain. On a flat-ish construction site with good visibility, differential levelling is going to be both easier and more accurate.

If you really want to look into trig levelling, here is some more info:

Presentation from above author

Posted : April 29, 2020 11:14 am
Ken Salzmann
500+ posts Member


The trig levels in JK's paper are not the same as measuring up the the instrument from your baseline point.  Give it a try; you may be surprised!


Posted : April 30, 2020 6:59 am
dmyhill and RADAR liked

1,000+ posts Supporter



In my experience, a well done trig loop is faster, easier, and more accurate than an auto-level loop (they are both differential leveling, in that you have a + off a backsite and a - to the TP).  

If you have Carlson, you can do it in your DC and you are even better off, in that you have no risk of writing something down incorrectly, and you can run a closing/balancing routine on it.

IF you have Carlson, the added benefit is that if you run GPS through points, then run your trig level through them, and use the same point numbers, it will create a report comparing the two heights, and it will overwrite the points with the trig loop heights if you would like. 

Carlson will actually do this for your auto-level as well.

Posted : April 30, 2020 11:55 am