User poll....error or...?

[dwescott]

I have a good idea, but thought I'd get some other perspectives on it.

You've got 2 points, about 4000 feet apart. Centerline alignment for a runway.

Initial stakeout at 100' intervals went perfectly as it always does. Not much involved in creating points on an alignment.

So here comes the question.

Survey crew needed 50' intervals, so they did a stakeout in the data collector between those two points....to fill in the 50' gaps.

Went to stakeout, nearest...and reshot the elevations at the 50's. Imported the new data into the project.

Few days goes by. We start looking at the data, and notice that the 50' points are off. They vary from .1' to .7' and are East and West of the alignment.

(To help you with your decision, the point for STA 1+00 was slightly east of the alignment....and that was created in CAD. The other 3900 stations are dead nuts on).

Were these points miscalculated or altered?

[sinc]

Couldn't tell you... Never seen anything like that.

Did your crew use the Alignment for station/offset stakeout, or did they calculate midpoints between the 100' stations?

[dwescott]

I've never seen this before...not sure exactly where the errors came from. It doesn't feel like an error. Survey crew doesn't make errors like this, which is another concern. He's taken responsibility for it, for what that's worth. Resetting the points to the correct elevation, taking the lanker out...but it doesn't fix the original problem, whatever that might have been.

These points have been dead on, every time we've gone to check in...until last month some time. Now they're all off, even the benchmark.

Off on X, Y and Z now as well. Not a lot...just enough to notice, or just enough to completely screw up construction had they not been noticed. A two tenths bump at a taxiway intersection would probably be a bad day.

[gjschaap]

Could it have something to do with using US Survey Feet versus International Feet?

[jmeyer.186809]

Couldn't tell you... Never seen anything like that.

Did your crew use the Alignment for station/offset stakeout, or did they calculate midpoints between the 100' stations?

sounds to me like they just calculated mids between the 100' stations which will give your errors. They should have used the extents and then checked grade every couple hundred feet for accuracy.

[dwescott]

I'm fairly sure the points were moved. They didn't match the surface or the alignments...not really much else that could explain it. Think this is the second project that has completely self destructed since I've been here.

Just moved to doing the work on my local machine and outputting whatever people need. I enjoy the work first time through. Second time it's just annoying.

[jmeyer.186809]

I enjoy the work first time through. Second time it's just annoying.

Agreed! I hate to do it a second time through.

[Coolmo]

There are so many ways to import these points from the collector I'd try looking into the import process to see if any weird transformations were made or if any check boxes were missed for specific data on the import.

[dwescott]

We haven't been able to track down any obvious problems with the survey gear, but the collector has been acting strange since the last time it was serviced.

The errors just didn't make sense though. The majority of them were dead on, but there were enough points off either vertically or horizontally I had to toss all the data. Just wasn't confident in it any more. For the 8 or 9 months the data sat on the server...it was fine. Topo was spectacular initially...very good survey work, with all the major items covered.

Fell apart in days...and reminded me of another project at another employer that kept getting items inserted into it (200,000 micro donuts in one corner)...or data that kept moving....(stakeout that had a few points off on the vertical by 80 feet)...

Fairly confident I know what it is...just can't say it out loud. We've all seen it before in this industry. Started storing projects locally, and they have no problems. I'll export one for the server copy.

First survey in the snow, second in 115 degree summertime. Not sure which I preferred...but hopefully there won't be a third trip.