I have been working on a 2.5 mile road project, using Topcon Gps shot some last vweek and finished up this week,4 days total. Contours looked great except for one day,i had a 500 ft section of road with my shots out 1 ft plus or minus on the west end of project and a 1000 ft stretch on the east end everything else was fine except for these shots on this day,all data was collected from the same base setup. rod height never changed and all HI's of base were checked in raw data. What could cause this? Yes I was fixed on all of the bad shots.
multipath?
Hi voltage overhead wires; chainlink fence; steel bridge in vicinity?
Classic, a bad fix!! First thing to learn about RTK is fixed does not MEAN fixed, it means your probably fixed.
Were you measuring in what Trimble calls 'continuous mode'? RTK shots are logged automatically at a user specified time and/or distance interval. Typically the operator is not looking at the data collector during this time but instead concentrating on moving the rover along an alignment.
Sudden acceleration of the antenna ( jamming the pole in the ground, etc ) can cause a loss of lock condition where the solution may degrade to a float solution for a short time until it reinitializes on the fly.
You would need to open up the field file and examine the metadata to see if that was the case. Just a guess on my part but I have seen it before.
On a happier note, you caught it using the checks and balances you have in place.
I had a similar anomaly with my Topcon the other day. The elevation bust was on the order of a few feet, but the 'quality indicators' from the job file were rock steady. The lesson learned should be the data collector can't tell you what it doesn't know. You are spot on that check procedures are not optional...
What kind of Topcon equipment? Our original set of Hipers we had (no glonass) would get a bad solution and stick with it until you lost lock and it got fixed again. In open ground you will never get a bad intilization but if you get near a building or trees it can do an on the fly and be bad. I've had this problem the most when the unit was mounted on a 4 wheeler. Our Hiper II's seem a lot less prone to this problem.
In open ground you will never get a bad intilization
Never say never:-(
I've had them in open ground a lot, not as often these days, but still.....
We by are running hyper V units. We experience a bad init in the open one or two times a month. All of our control and boundary is either redundant 30 by 30 second RTK or we simply gather static.
