Dignity of Calls - Coordinates

What got into you today Shawn? It's Saturday and you're not supposed to think this hard! 🙂

But you do make valid points!

And while I know about the hierarchy of evidence, I suspect the reality is that we weigh all the evidence and give appropriate weight to everything.

Exactly. I'm advocating for the freedom to apply proper reconstruction procedures dependent upon and consistent with the method used to construct the original survey.

I'm on a slow return to Texas from California. Delta had serious issues with connections and it has turned to planes, trains and automobiles scenario. But it was a great week in Silicon Valley, so I'm not complaining. But I'm certainly not feeling "Saturday".

Dignity of Calls - Coordinates - Last Is OK

"The requirement is that the original survey be based on precisely determined coordinates."

Given a written document to that affect the priority of coordinates might increase.

But since coordinates have many more numerals than other descriptions, there is a greater probability that they are prescribed wrong.

Under previous decisions on the law of boundaries, the coordinates must also be in their original positions. Absent a clear and defined reference frame and other metadata that possibility falls apart quickly.

There is no need to rewrite the law.

End of discussion.

Return to your weekend.

Paul in PA

Not to go off on a tangent but here's a real world scenario which still leaves a bad taste in my mouth and concerns coordinates:

Survey of a large pre-EDM subdivision for major R/W takings. Urban, hilly, non rectangular lots, brushy in some areas. At one existing internal 2+- acre parcel (fire station) found all record monuments in good condition within +-0.10' of their calculated search coordinates (typical throughout the subdivision) except one, which was 1.5' from its "record" location. I held it and worked up the RoS which I was to sign. My "supervisor" (we were both licensed at the time, me ten years longer than him) exploded and said that monument must be disturbed, it's not close enough to its calculated position -- report it as disturbed and set a new monument at the "correct location" (coordinates).

I pointed out the field recovery notes reported "found per record in good condition", went out and poked around, no sign of post subdivision earthwork, sloughing or having been knocked about; fenceline, retaining wall(!), setbacks, et. al. honored the monument. He was adamant and had the party chief change his recovery field note to read " . . . , disturbed" (which put a bad taste in his mouth too). He chided me for being unwilling to "fix" a blunder the original surveyor made. I congratulated him for creating some fairly major physical encroachments where there were none prior.

I cringe that some future surveyor will follow my footsteps and question why I "pincushioned" a perfectly good corner. Um, *coordinates* told me to?

There are several variations of the Doctrine of Priority of Calls. The real goal is to logically weight the evidence to provide the boundary determination.

A coordinate could be weighed the same as a monument in certain circumstances just as an abutter could be weighed as a monument. The weight of a monument could be dropped.

Dignity of Calls - Coordinates - Last Is OK

Coordinates need not be spelled out but can be produced from vector addition from direction/distance calls from an assumed origin.

>creating some fairly major physical encroachments

Existing monument, no evidence of disturbance, and RELIANCE! Whether it's coordinates or distances, that's just a bad decision.

Agreed

What I'm describing would have no affect on intent, junior senior rights, or monuments.

'Correct' as relates to monuments is an identity, not a distance....

Shawn, Your Coordinates Have No Priority...

...over the direction/distance information that created them.

I assumed you were talking about Real World Coordinates based on information other than the immediate direction/distance calls.

You are sitting in the car with your foot on the brakes and merely spinning some wheels.

Paul in PA

>
> With consideration given to the reason for this order, I wonder if it is time to consider reordering the the significance of direction, distance and coordinates. Now, when I say coordinates, thoughts no doubt immediately jump to State Plane, but this need not be so.
>
>[...]
>
> So how would a coordinate reconstruction differ from a direction and distance reconstruction? My answer would be that a coordinate based reconstruction would use a Helmert 4 parameter transformation to compare the original coordinates to the reconstruction survey.

Well, for starters, you would insist upon the coordinates referring to a grid with an independently reproducible orientation. The Texas Coordinate System is an obvious candidate. Secondly, you would insist upon the scale of the grid being known. If you have those two quantities known, the use of the coordinates is simply computing the average offsets in N and E of recovered markers with specified coordinates from nominally the same grid as reconstructed by a resurvey.

To make that real easy, you'd want to have some permanent reference markers that were both highly stable and highly GPSable from which the offsets could be computed, preferably on different ends of the project. You'd ideally also want to have the uncertainties of the "record" coordinates in the form of their standard errors in relation to both the local segement of the CORS network and one of the permanent reference markers by the project site.

I personally do not believe that the world is ready for coordinates to control where monuments and boundaries are or are not.

"Whose coordinates?" and "What are they based on?" are something that is still in debate.

As of now they are each and every surveyor and technician's tool and none of them agree with each other within 0.04ft.

[sarcasm]Someone will come along and Patent a coordinate system that all their work is based on and then where will we be.[/sarcasm]

Shawn, Your Coordinates Have No Priority...

You should read more closely. My original post was clear on this.

Not really. Scale and orientation can be determined from a minimum of two monuments. More monuments, with good relative geometry allows for an over determined solution with residuals.

Having a known orientation and scale reduces the minimum required monuments to one, for translation. Again, more is better but geometry becomes less important (practically inconsequential).

I'm not suggesting coordinates replace monuments, I'm suggesting that local coordinates (a coordinate system that is only related to the other coordinates in a boundary) are superior to calls for directions and distances, because the directions and distances in modern surveys are derived from coordinates to begin with (Whether geo-referenced or not).

> Not really. Scale and orientation can be determined from a minimum of two monuments.

But not reliably since there is no check upon the positions of the monuments and so the connection between them and the coordinate system remains undemonstrated.

>More monuments, with good relative geometry allows for an over determined solution with residuals.

Except the residuals aren't exceptionally useful unless you have an idea of the scale of the coordinate grid and the uncertainties of the coordinates.

> Having a known orientation and scale reduces the minimum required monuments to one, for translation.

The obvious problem with that would be that unless the uncertainties in the coordinates of the one monument were known, the uncertainties in the computed offsets in N and E would also be not very well known.

Just think this one through.

You're given the coordinates (in US Survey Feet) of some monument as:

[pre]
N = 3117657.16 +/- E1
E = 13846660.43 +/- E2
[/pre]

if E1 and E2 are 0.03 ft., and your coordinates are +/-0.05 ft., then the uncertainty in the North offset and the East offset is SQRT(0.03^2 + 0.05^2) = 0.06 ft.

So, to mark a given coordinate postion that itself has some uncertainties with respect to your reference monument, you add the offsets to the N and E values to make them fit your coordinate system +/-0.06 ft. in N and E. Then you go survey those coordinates with an uncertainty of +/-0.05 ft. in your own work. That means that even with zero uncertainty in the record coordinates, your relocation of them has an uncertainty of :

+/-0.08 ft. in N and in E.

if E1 and E2 are different, and your coordinates have different uncertainties in N and E, then the uncertainties in the North and East offsets are likewise going to most likely differ.

If you have three or four monuments with similarly uncertain coordinates that you also position with similar uncertainties in your coordinate derivation, the uncertainties in the offsets should be half of those derived from one monument.

Right. This is the beauty of the Helmert transformation. Residuals provide our check. So if we have no independent bearing source outside the survey being retraced (such as State Plane Grid, astronomic, etc.) two monuments are minimally required while a third (or more) provides us residuals as a check. Assumptions can be made regarding scale. You are correct about uncertainty with one monument, however, this uncertainty equally affects retracement by direction and distance or by coordinates. So it has little effect to the discussion of dignity of calls.

I would agree that coordinates, bearings and distances are and can be used in the same sentence as to their rank among superior calls.

Each one is derived from a measurement made by a surveying instrument and equally share a certain degree of accuracy and amount of error at the same time.

We know that we are close enough to sign our name to the results and at the same time know that we are not exactly correct, but close enough.

It is a grand idea to have one system for all. I believe there is a lot of discovery to be made from all the existing data of locations around the world and I wonder if and when it can be post processed into one usable solution.

The fact that the Earth is constantly reshaping from natural events may make that impossible.

Isn't the great down under on one Queensland system.

> Right. This is the beauty of the Helmert transformation. Residuals provide our check. So if we have no independent bearing source outside the survey being retraced (such as State Plane Grid, astronomic, etc.) two monuments are minimally required while a third (or more) provides us residuals as a check.

No, using a 2D or 3D Helmert transformation (translation, scale and rotations about one or three axes) on only two or three points is a very inferior way to reconstruct a coordinate system. The reasons should be obvious if you know basically nothing about the orientation or scale of the record coordinate system, as would be the case in a typical RTK survey that used a "calibration" or "localization" (but without, of course, mentioning the projection parameters generated by the same).

Whereas, if you have coordinates in a grid of independently reproducible orientation and known scale, the results from only two or three points will always, no exceptions, be superior.

A simple demonstration would be to take the theoretical coordinates of three points arbitrarily chosen, multiply them by a scale factor differing by about 50ppm (1.000050 or 0.999950) and add random errors in the N and E values drawn from a normal distribution with a standard deviation of 0.10 ft. to generate the "record" RTK-derived coordinates. Then take the theoretical coordinates and add random errors to the N and E values drawn from a normal distribution with a standard deviation of, say, 0.04 ft. to generate the "as found" coordinates. Solve the transformation parameters for those two sets.