For some time now I have wondered how others view/treat the following topic area:
(Background) My understanding is that when the various State Plane Coordinate Zones were being developed, one of the design goals was to create zones which had a maximum error (grid to ground) at the fringe of 1 foot in 10,000 feet. That was in recognition of (I have read somewhere...don't ask where as I forgot) accepted accuracies of that time for chain and transit boundary surveys, in order for State Plane coordinates to be used directly for survey/map/description distance purposes while satisfying accuracy requirements. Also, likely other states have as Florida does, for example, set the following accuracy requirements (or something similar) for boundary surveys: 1:10,000 closure error is the minimum for Commercial/High Risk (1:7,500 = Suburban; 1:5,000 = Rural).
For years and years boundary surveys were made with chain and transit, whereas the above accuracies were certainly achievable using proper field methods/equipment. By the late 1980's I had already performed several thousand boundary surveys myself, and to this day none of them have ever been discounted or even challenged for lack of “perfection”, having been done within the accuracies stated above. In addition, I have heard nothing in recent years to indicate that it would be illegal for a surveyor still to this day, to perform a boundary with chain and transit so long as he/she achieved the requisite accuracy for land type. Accepting the above, what then is the problem of making boundary surveys today using GPS that would accomplish accuracies meeting State standards (points would also be at least as accurate as those set by chain and transit surveys), and which could be done without applying all the adjustments needed for “near perfection”?
I think most would agree that with GPS you can achieve extremely accurate positions (likely exceeding equivalent accuracies in the 1:100,000's and up), when incorporating all the available adjustments. That's not the question, however. What I am attempting to learn is whether anyone can explain how their Board actually does require a boundary survey using GPS equipment, to be more accurate than it would be for the same survey if using chain and transit? Or for that matter, has their Board perhaps outlawed chain and transit methods for boundary surveying?
I am not asking this to offend anyone. I realize there are likely a good many on this site who may even be offended that any true “professional” could ask such a question; and, that a good many here strive for perfection and anything less would absolutely pain them. Good for you if that describes you. You certainly have my admiration. But, in Realville how would it be a violation of law/rule in your State, if you worked directly in State Plane coordinates for your inversed bearings/distances which appear both on your maps and within your legal descriptions? So long as your accuracies met those of the surveyor performing a chain and transit survey, realizing that for decades such surveys were certainly a non violation?
One benefit if accepting such “less than perfect” coordinates (i.e. coordinates whose inverse does not yield the exact correct ground distance), would be the creation of a county GIS type of map upon which your survey company could begin adding their boundary surveys, with coordinate positions which could be used interactively for all future nearby survey work.
(The following describes the GIS I developed for my business...taken from an earlier posting. Fortunately, for us everything is near sea level, and the scale factor next to nothing... : “We operate primarily in one small county in Florida. Approximately 10,000 individual surveys. Started using GPS in mid 1990's, and by 1998-99 every survey was done in state plane. Approximately half of our surveys are in state plane. Currently have about half of all sections (Florida is a PLSS state) in the county broken down in state plane coordinates. About two thirds of all highway centerline is also tied to state plane. I have one very large AutoCad master drawing showing all monumentation, section breakdowns, centerlines, etc., as well as the boundary lines of each surveyed tract drawn in state plane position. Also, aerial photos are on layers which mostly remain off, but if needed can be switched on. Also, I have a separate cogo file for all points situate within each individual section. Whenever I wish to work (draw, calculate, etc.) within a given section, I just make that particular cogo file current. A typical cogo file would be named Section 29-45-35.crd (e.g. for Section 29, Township 45 South, Range 35 East). Inside that file would be all points situate within Section 29-45-35. I use Carlson and AutoCad. It takes someone very disciplined to keep the map updated. The young bucks in my business have never seen the advantages, so I have had to just accept the fact that if I don't do it it won't get done.”)
Flame away!
ibenhavin
I sometimes wonder what those required precisions really apply to? If you are traversing 4 miles around a section to close within a little over 4 feet (for 1:5,000), I can see that. But for the guy that surveys 60'x90' residential lots every day, does he really have to close that boundary to less than 0.04' and the 60' lines have to be measured to less than a hundredth (for 1:7500)? In my experience, I have found that the boundary precisions you get don't really tell you much other than if you made a blunder or not. I don't find them to be very objective in judging positional accuracy.
The Bow Tie Surveyor
My understanding is that when the various State Plane Coordinate Zones were being developed, one of the design goals was to create zones which had a maximum error (grid to ground) at the fringe of 1 foot in 10,000 feet.
Not quite correct. The goal was to keep the ellipsoid to grid factor at less than 100 ppm. The assumption was that ground distances would be reduced to sea level to be reported. That part of the equation was never accepted as standard practice.
What I am attempting to learn is whether anyone can explain how their Board actually does require a boundary survey using GPS equipment, to be more accurate than it would be for the same survey if using chain and transit? Or for that matter, has their Board perhaps outlawed chain and transit methods for boundary surveying?
the Board should be interested in results and the professional judgement used to get the results, not the tools used to perform the survey. If you can achieve the required relative accuracy with a compass and chain why would there be a problem?
would it be a violation of law/rule in your State, if you worked directly in State Plane coordinates for your inversed bearings/distances which appear both on your maps and within your legal descriptions?
No. But you should document your coordinate system. In fact, in our state the survey chapter of code defines the plane coordinate system and how to reference the system in your survey document. It also says survey distances are to be referred to the horizontal plane. The only horizontal plane defined in the chapter is the state plane system developed by the federal government. Despite this rule the standard practice has been to use an assumed plane for each measurement rather than reduce each measurement to a common defined plane.
One benefit if accepting such “less than perfect” coordinates ....would be the creation of a county GIS type of map
This creation has already happened on many fronts. As an industry, boundary surveyors seem to participating as little as possible while kicking and screaming when they should have been leading the way. Indexing a firms surveys to a common grid system makes a lot of sense. It makes even more sense to reference all surveys done in the county to a common low distortion grid system for everyone to enjoy the benefit of. IMO It's never too late for surveyors to start leading instead of following.
> My understanding is that when the various State Plane Coordinate Zones were being developed, one of the design goals was to create zones which had a maximum error (grid to ground) at the fringe of 1 foot in 10,000 feet.
>
> Not quite correct. The goal was to keep the ellipsoid to grid factor at less than 100 ppm. The assumption was that ground distances would be reduced to sea level to be reported. That part of the equation was never accepted as standard practice.
>
Back in the 1960's I did read that somewhere when I was studying the creation of the SPC. Maybe they used 100 ppm instead of 50 ppm or 150 ppm or something else because they knew 100ppm would fulfill the desired practical accuracy(?). I dunno.
> would it be a violation of law/rule in your State, if you worked directly in State Plane coordinates for your inversed bearings/distances which appear both on your maps and within your legal descriptions?
>
> No. But you should document your coordinate system. In fact, in our state the survey chapter of code defines the plane coordinate system and how to reference the system in your survey document. It also says survey distances are to be referred to the horizontal plane. The only horizontal plane defined in the chapter is the state plane system developed by the federal government. Despite this rule the standard practice has been to use an assumed plane for each measurement rather than reduce each measurement to a common defined plane.
>
The only time I ever publish a State Plane Coordinate on an official document, is when I do work in some county which requires it for certain reference monuments shown on a new recorded plat of a subdivision. All other times the coordinates are strictly for our company's use/benefit. Also, the only SPC related notes we ever place on one of our boundary survey maps is regarding the basis of bearings we have used. Of course if the basis is Deed, Record, magnetic or assumed there is absolutely nothing regarding SPC anywhere on the map. But, this is Florida. Also, we are not required to state the type of equipment used for the boundary survey or the found accuracy.
I personally prefer a relative/absolute precision requirement, such as those outlined in the ALTA specs - makes much more real-world sense IMHO.
I believe StarNet can calculate error ellipses from transit/tape surveys.
Linebender gave great answers. The elevation factors combined with the scale factor can easily exceed 100ppm (which is equivalent to 1:10,000 - tomayto tomahto).
I see no reason why a surveyor should accept this as part of his error budget today though. There's no reason that a surveyor can't work in Grid (if he chooses) and not be subjecting his work to an automatic 1:10,000 error. Simply report the combined scale factor and call for Grid distances or apply the combined scale factor to your reported distances and be done with it.
We've been working with SPC and maintaining a CAD file with all of our work on it, since about 2000. What I'm discovering now is that SPC is okay, but becoming obsolete with the ability to work with low distortion projections. Remember, SPC was a system of developed projections to make it easy for surveyors to transform cartesian coordinates measured on the ground to georeferenced positions on the Earth (ie Lat/Long). Large areas were used for the zones, accepting large scale factors and convergence angles, all for the sake of simplifying the number of zones needed. Today, I develop low distortion projections that allow me to do the same thing and ignore combined scale factors because they are negligible (less than a hundredth in a 1,000 feet). I can easily transform coordinates in my home grown LDP to SPC if I wish or to Lat/Long or to another LDP, and back again, and my LDP's are more representative of real, on-the-ground measurements (north is pretty close to north and a 1000 feet is real close to 1000 feet).
Discussions like this, suggesting incorporating the combined scale factor into the error budget of the survey, is one of the reasons SPC has become such an impotent, bastardized system. The system itself is perfectly precise, but short-cutting unnecessarily has lead to confusion and distrust.
IMHO.
By the way. No flaming from me. Your work may be excellent, I simply disagree with what I think you are suggesting.
As to the tape and transit vs. GPS, I don't think the technology should distract from our primary responsibilities to interpret intent of land conveyances and place that intent in a defensible location on the ground. GPS, transit, shouldn't matter.
I do appreciate Texas's standards that sound similar to what you've outlined except that a 0.10 foot is included with the ratio. Neither GPS nor a tape is likely to provide 1:10000 precision on a line ten feet long (=0.001 foot). So a little absolute error to accompany the ratio helps out quite a bit. (The ALTA standards offer a similar approach).
>By the late 1980's I had already performed several thousand boundary surveys myself,
Dam you're old:-)
You can have data that is in SPC or collected in geodetic with GPS, and you can report it in ground distances every day of the week. Almost every state I have looked at statutes from allows you to use the SPC grid, but that does not mean you have to.
Relating grid to ground is just a relatively simple mathematical process that can be handled 4 or 5 different ways. Relating grid bearings to true or any other basis is equally fundamental.
As I think someone already stated. For Florida probably not a worry, but certainly obvious in Colorado. SPC is not going to be anywhere near ground because that 1/10,000 assumption in the SPC design does not include the elevation factor or in fact a number of other corrections after scale factor. But, in fact all those corrections are easy to determine and apply. Given any 2 SPC coordinates a grid inverse followed by application of grid scale and elevation scale will give you exact ground distance (well within 1:200K) which can be used on any plat or legal description.
It's been a lot of years since SPC existed as a major component of survey data.
It's been a lot of years since GPS has been a significant tool in the profession even if not everywhere.
Being aware of how to use data and datums is part of the profession, even if you don't have those tools, you should be bumping up against surveys done with them and have an understanding of what is involved.
My first flame would be, if you can't figure this out or get the CEU's or mentoring from someone on how to deal with all this after it being a significant part of the practice of land surveying for at least 20 years, perhaps you should self deport yourself out of the profession.
- jlw
Cornes described with State Plane Coordinates, etc.
The Code of Virginia contains the following section:
§ 55-296. Use of system not compulsory.
For purposes of describing the location of any survey station or land boundary corner in the Commonwealth of Virginia, it shall be considered a complete, legal, and satisfactory description of such location to give the position of said survey station or land boundary corner on the system of plane coordinates defined in this chapter. Nothing contained in this chapter shall require any purchaser or mortgagee to rely on a description any part of which depends exclusively upon either Virginia Coordinate System.
(1946, p. 168; Michie Suppl. 1946, § 2849(8); 1984, c. 726.)
Although this section does not directly address your question(s) it does tend to muddy our crystal ball, and bring into debate several issues about monumentation and “order of preference” when we are deriving our data from GPS observations which tend to be State Plane Coordinates.
MY take on this
SPCs are wonderful and GPS (as well as EDMs and total staions) certainly give us more precise (and probably more accurate) measurements than transit and chain. I believe what some lose sight of is the purpose of the survey. Are we to give "better" measurements, or are we to "find" the location of the property on the ground and report the facts in such a way as to make retracement of our surveys possible. I certainly make use of the best available equipment and data, but does finding a monument at 99.99' or 100.10' change the fact that the monument is still the corner (assuming it was to begin with)? I was told years ago, by a then sitting member of the Georgia BOR, that HOW we arrived at our conclusion was "our business" as long as we stated how we arrived at the conclusion. All a matter of professionalism.
Andy
(Background) My understanding is that when the various State Plane Coordinate Zones were being developed, one of the design goals was to create zones which had a maximum error (grid to ground) at the fringe of 1 foot in 10,000 feet.
I've understood that it was the grid scale factor that wasn't to exceed 1 in 10,000. If the elevation factor is combined the grid to ground can greatly exceed 1 in 10,000.
I also understand that this applies more to NAD27 than to NAD83.
It may be that Montana is an extreme example, but just the grid factor of the NAD83 system will exceed 1 in 2,000 in the middle of the state. The idea was to create a Lambert projection that never had a grid factor larger than 1. This placed a grid factor of 1 at the north and south borders of the state and less than 1 everywhere else.
I've seen grid factors of 6 feet per 10,000-that's without the elevation factor combined.
I've done just about all my surveys in State Plane over the years (beginning in the 70's).
It wasn't until GPS came along that I started to get away from state plane more often. I really only care about the Lats and Longs these days. If they are checking the coordinate system (whatever it may be) follows along.
Jerry...
do you realize how few of us would be left?!
Gads you fellas. Good discussion.
🙂
Completed a number of easement descriptions for a City of Columbus, OH and U.S. Army Corps of Engineers flood control project. Although used as easements all descriptions and mapping were required to meet the fee title transfer requirements for descriptions and maps in Franklin County Ohio. The formats and content of these also were required to meet U.S. Army Corps of Engineers standards.
These required inclusion of monuments stamped with a predetermined parcel and corner number. The descriptions were required to include these numbers as well as both ground and grid distances, citation of the coordinate system and the scale factor used for the project. The 1927 datum was used because the project control and engineering surveys were started before the NAD83(86) datum existed. Citation of Bearing basis also was required to cite the coordinate system grid north and true north convergence angle established for the project. As I recall this was at the approximate center of the project.
The map of each easement was required to include all the the above data as well as a table listing the coordinates of each monument. The map was also required to be recorded with the description.
Managed to find an example online if you are interested go to the Franklin County Recorder site "Instrument Search" option. Input either the instrument number 199605100117183 or the book 31950 and page D09. Then click on the "Detail Data" button, you should see grantor Central Ohio Transit Authority and grantee Columbus City of recorded 5/10/1996.
Click on the "Display Doc" link at the upper right of the record to view the document. Believe the records were originally microfilmed and later converted to tiff files. The map text is a bit unclear but the description is readable. Either should be sufficient to retrace the easements. We created dozens of these to support the project.
