Weird Coordinate Shift or Translation

[Ronald Murphy]

Here's what happened, as best as I can describe it:

We had a small residential property boundary survey in town where we were able to tie into a few lot corners from an older survey. The first day on-site (a Friday), we were able to collect data on about 15 points. We used a "Mifi Hostpot" and the Missouri Department of Transportations Coordinate System. The following Tuesday we began to set corners based off of the data we had collected on Friday and the corners from the old survey.

But when we began to set the corners, we noticed that maybe they were not lining up properly. We dismissed it at the time because of a rock wall that may have been playing tricks with our eyes and due to an impending storm.

A couple days later we returned and decided to check some of the points we had shot the first day. On each point, our Triumph was telling us that we were off about 2 1/2 feet off both North and West.


Since each point was off relatively the exact same distance and bearing, there must have been some type of coordinate shift or translation.

Is there anything that I could have done differently on the first day compared to the others that would explain this? I don't mind at all if it was a user error on my part, I would just like to know what I possibly did, so that I don't repeat the same mistake.

Thanks

 

[Shawn Billings]

Reference Frame might have been WGS84 instead of NAD83. It would have about that much difference.

 

[Ronald Murphy]

Reference Frame might have been WGS84 instead of NAD83. It would have about that much difference.

We tried to go back and set the reference frame to WGS84 because we had the same thought, but when we did we were only off by a couple tenths each way. Again, I may not have been fully in the WGS84 reference frame. I've only had the unit for a couple months, so I'm still working out some kinks on my end.

 

[Shawn Billings]

After the point is created, it makes no difference switching the reference frame as the point will simply transform with the change. The coordinates don't stay the same, they change with the change in transformation. So, the point must be created with the correct transformation for the correction source. Generally, in the US, you want EVERYTHING to be NAD83 in the LS. Base reference frame and coordinate system. If there is a mismatch, you'll see about 3 feet in horizontal and 4 feet in vertical (the exact value will vary depending on where you are).