In Texas, a surveyor preparing a map or written description of a tract of land is supposed to state what the basis of the bearing shown upon it is, i.e. whether they refer to grid North of a particular zone of the Texas Coordinate System of 1983, astronomic North observed at some particular station, or some line between two monuments in place on the ground assumed to have a particular bearing as previously reported. But it is simply amazing what a variety of strange notes are produced to express this simple information.
My current favorite is one I found in the public records yesterday in a written description produced in 2009. I've reproduced it exactly as written in the record :
>"A Global Positioning System was used to the establish the orientation of the bearings."
This has to be another major triumph for RTK GPS!
"A Global Positioning System was used to the establish the orientation of the bearings"
I see no mention of "RTK" in that quote. Maybe he used Static, maybe not!
In any case, that BOB is substandard (and ambiguous) at best!
When properly (and applied), RTK is a wonderful tool. Like all tools, it can be misused, misapplied, misunderstood, or just plane FUBAR'd.
Loyal
According to this article there are three Global Positioning Systems currently in operation, and two more in development. [sarcasm]So which one did this guy use?[/sarcasm]
The one in his machine?
> "A Global Positioning System was used to the establish the orientation of the bearings"
>
> I see no mention of "RTK" in that quote. Maybe he used Static, maybe not!
No, the note pretty much has to be the work of an RTK user. RTK is just a magnet for this level of cluelessness. Post-processed GPS? Not so much.
> According to this article there are three Global Positioning Systems currently in operation, and two more in development.
Actually, wouldn't you say that GLONASS et al. are part of a Global Navigation Satellite System and refer to what the US Department of Defense runs as the Global Positioning System? It's sort of funny that the surveyor noted that a Global Positioning System was used, not the Global Positioning System, as if DoD is running several.
I know I posted this before. It is nowhere near the ellipsoid height... And it is on a plan of land where there is no feature controlled by the vertical. No other mention of GPS on the plan, nor are any of the corners documented with LAT/LONG, XYZ, or SPCS.
>
It's a decent entry, but to really be competitive, shouldn't that read as follows?
"BENCHMARK:
Top of Concrete Bound
El= 73.68 per a Global Positioning System Datum"
I will call the PE/PLS who prepared the plan and tell him to change it.
Mine can be the winner of Basis of Elevation when no elevation is required. Yours can be the winner of You are the example of why people should be educated before they are allowed to use GPS. It's just like how you need a license before you can drive a car.
73.68 what?????
Smoots? Smokes? Meters? Australian Cubic Feet?
> > "A Global Positioning System was used to the establish the orientation of the bearings"
> >
> > I see no mention of "RTK" in that quote. Maybe he used Static, maybe not!
>
> No, the note pretty much has to be the work of an RTK user. RTK is just a magnet for this level of cluelessness. Post-processed GPS? Not so much.
You've never encountered someone who uses post-processed GPS that didn't know what they were doing? Have you been living under one of those rock mounds?
I have seen this notation in the past and took for what it was worth. If you know what I mean…
Two situations, that I thought that this occurred.
One was the advent of inexpensive L1 units like the Promarks etc. Uninitiated GPS users delved into using these units with no training. Some realized that they were in over their head without training.
Some smartly returned the units and some eventually got training or hired someone with GPS experience.
The second situation... Surveyor would hire a local to establish them a GPS pair for bearing and elevation mark. They would be provided the bearing and elevations with no metadata attached since they really did not need it or understand it.
There were few surveyors providing that service here. A few were very good surveyors and their work was probably spot on. But there was one, who I think was doing a moonlight from a state agency that was providing GPS points with L1 units. They might have been using state equipment on weekends.
He might have caused a lot of problems at the time that he didn’t think would catch up with his work until years later.
> You've never encountered someone who uses post-processed GPS that didn't know what they were doing?
The odds are very much against it. The folks who didn't want to deal with the nitty gritty of positioning and adjustment bought RTK because it produced numbers without all that head-bustingly difficult stuff that post processing required. The appeal of RTK was (and probably continues to be) that you just send your minions out into the field to come back dragging a data collector full of coordinates to dump them into a map. What I posted is the perfect bearing basis note for that style of practice.
> I have seen this notation in the past and took for what it was worth. If you know what I mean…
Yes, I do know what you mean. I like these dumbass notes because they let me know that it's a clusterfuge effort and not to worry if things look seduced because there's a good reason.
What would the Basis of Bearing be if you set up on an autonomous position and used the GPS bearings is gives you?
> What would the Basis of Bearing be if you set up on an autonomous position and used the GPS bearings is gives you?
How about:
>Basis of Bearings : Bearings refer to a direction that I think may be North, but I'm not sure whether it is Grid North, Geodetic North, or RTK North, so don't say I didn't warn you.
I usually include a note describing stating that the bearings are grid north based on GPS observations conforming to the appropriate State Coordinate System, datum and zone (which are usually defined by state law) and then give a convergence angle at a convenient monument (usually the point of beginning). For my current project, the note looks like this:
BEARINGS ARE REFERENCED TO GRID NORTH, BASED ON GPS OBSERVATIONS AND CONFORM TO THE NORTH DAKOTA COORDINATE SYSTEM OF 1983, NORTH ZONE (INTERNATIONAL FOOT). THE CONVERGENCE ANGLE AT THE POINT OF BEGINNING IS __°__’__._”.
I also give information about the distances being grid and provide a combined scale factor for conversion and I described my elevation datum.
I was looking for a professional opinion and explanation.
What is the bearing that is given when you are using a ground calibration? A ground level survey with no projection and no datum for GNSS.
> I was looking for a professional opinion and explanation.
>
> What is the bearing that is given when you are using a ground calibration? A ground level survey with no projection and no datum for GNSS.
Well, your "ground calibration" was based upon the assumption that the line between two monumented points had a certain bearing, didn't it? The note would be along the lines of :
>Bearings of lines noted hereon refer to the West line of the Such-and-Such tract, found marked upon the ground by monuments numbered [no.] and [no.] as described hereon and taking the direction of that line to be [bearing] as set forth in [give reference to record upon which the assumption was based].
There's no need to mention RTK unless you think it is good to warn future surveyors that things may have gone haywire.
