We've all seen these before. The odd thing about this one is that it's recent, that part is unusual:
While I would never put that exact statement on my survey, I have seen very similar ones. I don't have any issue with this statement as long as it meets the state requirements. In Idaho, this statement doesn't. After all, I'm going to go search for and tie the monuments on whatever system i choose, which is always state plane. I prefer this over an assumed meaningless bearing along a random line.
This must be a local coordinate system, right? A surveyor wouldn't say "gps grid" if they were operating in a published coordinate system, right? 🤦♂️
Looking at the bearings it appears that it's some type of "true north". Kinda close to the 1914 GLO plat, and SPC should be about 15minutes from "true" at this location.
Help me out. What is a GPS grid? Am I to infer the basis of bearings is geodetic or am I to infer the basis of bearings is State Plane Grid but he used GPS to measure those grid bearings?
Currently I am incapable of following his bearing base because I don't know what it is.
I'm not familiar with the GPS Grid. Locally, if using State Plane (and we typically do), we use the Idaho West Zone. If our control is performed with GPS, we will state the epoch and provide the deflection between Grid North and Geodetic North at a particular monumented point. Otherwise, we state a bearing as measured between two found, undisturbed monuments which are likely to remain undisturbed.
A basis of bearing that cannot be readily reproduced is useless. Since there isn't enough info to reproduce GPS Grid, it's useless and negligent (or perhaps evidence of incompetence).
I would say the only thing you can glean from the statement is that the bearings are not geodetic, I'm assuming that they are plane cartesian of some sort with plan north equal to geodetic north somewhere near the location, were that might be I will probably be able to figure out from field surveys,,,,,,,,,,,,if I want to spend the time.
A basis of bearings is between two physical points, that were actually visited.
Calling a plat or a SPC as the basis of bearings is simply unacceptable.
Leaves a lot to be interpreted. Seems consistent with someone throwing up the base and using a 'Here' position on a local grid projection. Of course the problem with these is they rarely tell you where that base was positioned and without that info, getting back onto those bearings requires ties to at least a couple of the corners. One of our more prolific local surveyor publishes an OPUS solution for where his base was for the survey and that's helped me out a lot when I've had to retrace his work.
Guess it's better than nothing? At least you know it's based on or relative to gps grid or gps grid geodetic/geographic NORTH 0° vs magnetic north or something completely arbitrary.
I've seen a surveyor who uses this statement: "Basis of bearings is GPS." And his north arrow is the typical cross with an arrow on top, but instead of an "N" in the center of the cross, it's a GPS satellite icon with the letters "GPS" on it. I guess it lets you know the basis could be absolutely anything.
With today's technology I don't really care much about the basis of bearing statements on surveys. Although they do need to meet state requirements. Every county we work in has some form of GIS base mapping that we can use to get us going in the right direction. We also have substantial internal, monument based, state plane databases in our primary counties.
"Basis of Bearings is GPS"
Those are the worst, could be "true", could be LDP of some sort, could be SPC, could be anything.
One of the most useless statements in surveying.
