Does All Metadata Look the Same in the Dark?

> Ah, have to love the metadata as a great clue as to who maybe knew what they were doing and who maybe didn't.
>
> Case in point: two surveys of the common boundary between two tracts, both calling for what the record indicates are the identical monuments at 1, 2, 3, and 4:
>
> [pre]
> Surveyor A Surveyor B
> (1996) (2013)
>
> 1-2 N44°00'34"E N43°35'10'E
> 1961.46 ft. 1961.59 ft.
>
> 2-3 N43°37'20"E N43°11'38"E
> 902.58 ft. 902.42 ft.
>
> 3-4 N42°22'39"E N41°57'30"E
> 450.24 ft. 450.23 ft.
> [/pre]
>
> Surveyor A describes his bearing basis as follows:
>
> >"Bearings correlated to the Texas State Coordinate System, North Central Zone, 1983 datum"
> Surveyor B describes his or her bearing basis as follows:
>
> >"Basis of Bearing being State Plane Grid - Texas North Central Zone (4302) NAD83 as established using GPS Technology in conjunction with the RTK Cooperative Network. Reference frame is NAD83 CORS96 Epoch 2002.0"
>
> Knowing just those facts, who would you want to bet on being closer to correct?
>
> What if I told you that the average mapping angle along that line is 0°25'35" (Grid Azimuth = True Azimuth - 0°25'35")?
>
> This also shows the power of standard projections. It was immediately obvious that one of the surveys was grossly erroneous as far as bearing basis went. It was also immediately obvious what the probable source of the error was.

My guess is that your 1996 survey, with its supporting metadata, supports your disdain of the way some surveyors use RTK to control sensitive items such as the boundaries of some lands.

> > Surveyor A describes his bearing basis as follows:
> >
> > >"Bearings correlated to the Texas State Coordinate System, North Central Zone, 1983 datum"
> > Surveyor B describes his or her bearing basis as follows:
> >
> > >"Basis of Bearing being State Plane Grid - Texas North Central Zone (4302) NAD83 as established using GPS Technology in conjunction with the RTK Cooperative Network. Reference frame is NAD83 CORS96 Epoch 2002.0"

> My guess is that your 1996 survey, with its supporting metadata, supports your disdain of the way some surveyors use RTK to control sensitive items such as the boundaries of some lands.

Well, to tell the truth, neither metadata statement is what I'd particularly want to endorse with my own seal and signature, although Surveyor A seems more obviously clueless if his survey from a "HERE" position in a coordinate grid oriented to geodetic North at the base station was thought to have been made using the Texas Coordinate System of 1983.

I haven't really investigated why Surveyor B's work in 2013 exactly matches the last survey of record in 2002, but it would be nice to think that the 2002 work was also by Surveyor B. With RTK users, it's always a roll of the dice.

"...grossly erroneous as far as bearing basis went. It was also immediately obvious what the probable source of the error was.

I'd feel fortunate that either surveyor even tried to use State Plane Brgs.

N

School me, Kent.

"This also shows the power of standard projections. It was immediately obvious that one of the surveys was grossly erroneous as far as bearing basis went. It was also immediately obvious what the probable source of the error was."

OK, Kent, I'll display my ignorance and ask you to elaborate on all of the above.

What is an "average mapping angle"?
What Metadata would you consider to be the minimum usable?
Is Metadata only necessary with GPS'ed surveys?
If most of a survey was done conventionally, how would you indicate the reduction to SPCS on a map?

Dave

I'm still looking to see where zone 4302 is. Not in Texas, 4201 to 4205.

School me, Kent.

> What is an "average mapping angle"?

Naturally, the mapping angles at Stations 1, 2, 3, and 4 are all different. The average for the line is just the average of the extreme values.

> What Metadata would you consider to be the minimum usable?

Well, if you're expressing bearings in the Texas Coordinate System of 1983, you should:

a) mention the zone,
b) describe how the bearings were derived,
c) use language that will inform later surveyors as to whether you really had a clue or not.

For example, if you really aren't very clued in, giving the DATE that you determined Grid North would be excellent as a warning to posterity.

> Is Metadata only necessary with GPS'ed surveys?

If you have to ask, apparently it isn't. :> (The straight answer is, of course, "yes").

> If most of a survey was done conventionally, how would you indicate the reduction to SPCS on a map?

You'd give the method by which the survey was oriented to grid North, the means by which you connected to NAD83 (presumably via monumented control points) and the published positions that you assumed those control points to have. Extra credit would be to give the uncertainties in relation to those monumented control points in some fashion.

> I'm still looking to see where zone 4302 is. Not in Texas, 4201 to 4205.

Texas Coordinate System of 1983, North Central Zone. That was me trying to read the note that said "4202" on the highly reduced plat with a magnifying glass.

This post and others show that RTK has not improved boundary work in my area at all. In fact in some cases it has gone the other way.

"Gitter done".

> I'd feel fortunate that either surveyor even tried to use State Plane Brgs.

Sure. It means that the common lines of adjoining tracts should have nominally identical bearings, so FUBARs are obvious.

School me, Kent.

Thanks Kent.

Dave

>With RTK users, it's always a roll of the dice.

The limits of your experience do not define professional standards.

Eventually these comments add up. I would make no comment, except non-surveyors may read this and then have needless concerns regarding the use of GNSS.

I am an RTK user, and I am unaware of any respected firm in my area that does not use RTK. The use of RTK is no indicator one way or another of ability or judgement.

As for metadata, the datum (including epoch, if applicable), and how and where (physical monuments) you tied the datum to your project, is the minimum. In my opinion.

And for the record, I acknowledge that Kent exceeds me in knowledge, ability, and as a successful surveyor.

His knowledge is impressive and a help to many of us. His commitment to do every job excellently serves as a standard and encouragement to me, and at times humbles me.

I assert that insulting and encompassing generalizations do not serve our profession nor the people it serves. I actually find it incongruous and damaging to ourselves.

> >With RTK users, it's always a roll of the dice.

> I am an RTK user, and I am unaware of any respected firm in my area that does not use RTK. The use of RTK is no indicator one way or another of ability or judgement.

I'm sure that eventually I'll see a survey that was made with RTK that doesn't have something spastic going on, whether a wild shot that didn't get checked, a surveyor in too much of a hurry to waste time actually digging for evidence, or you name it. There is nothing inherent in the technology itself that would prevent acceptable results. The problem with the first wave of RTK use was that it was marketed as an alternative to actually knowing anything about projections, "the GPS total station", so there were lots of users running around calibrating and beeping.

As I think you may have in mind, network RTK does more of the thinking for the surveyor, and may even do a better job of flagging inappropriate use, so it may be a step in the right direction.

The underlying problem is that when all you've got is a hammer, everything looks like a nail and when all you've got is a nail gun, the cabinet work will tend to be ugly.

Well said...

... Very respectful.... FWIW, I agree.

David

Your question was directed at Kent, but this is how I would have written the metadata statement.

BEARINGS are based on the Texas Coordinate System of 1983, Texas North-Central Zone per GPS observations. All coordinates are U.S. Survey Feet, NAD83 (CORS96) Epoch 2002.0 per static GPS observations and an OPUS solution through the NGS website. To get geodetic bearings, rotate the bearings shown hereon, clockwise, 00°25'39". All distances are grid and to get surface distances, divide the distances shown hereon by 0.9999XXXX.

Since shucking State Plane our Metadata is very simple

Bearings related to a local grid having an origin of N Lat: Y and W Long: X
Distances are expressed in US Survey Feet as measured horizontally along the surface of the Earth.
Geographic Coordinates are referenced to NAD83, 2011 Adjustment, Epoch 2010.

Since shucking State Plane our Metadata is very simple

> Bearings related to a local grid having an origin of N Lat: Y and W Long: X

Yes, what a freaking nightmare: each tract with its own projection. What a giant leap backwards.

Since shucking State Plane our Metadata is very simple

Is there a standard of practice in Texas when it comes to doing boundary work using RTK or is this the 'wild west' you're talking about.

Since shucking State Plane our Metadata is very simple

> Bearings related to a local grid having an origin of N Lat: Y and W Long: X
> Distances are expressed in US Survey Feet as measured horizontally along the surface of the Earth.
> Geographic Coordinates are referenced to NAD83, 2011 Adjustment, Epoch 2010.

This fixes the relationship between the grid origin and NAD83, but what fixes direction?