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Please talk me back into State Plane
Posted by shawn-billings on January 17, 2014 at 6:30 pmI’ve got a project I’m finishing up for a utility company. I developed a LDP system for the company as we do a great deal of surveying for engineering design for them. I chose to use an LDP as the State Plane combined scale factor for this area is on the order of 0.99989… That’s a tenth for every thousand feet.
We are now working on a reroute of existing utilities along a new TxDOT highway. TxDOT uses a “modified” State Plane System (State Plane scaled at the origin to accommodate surface distances). So now I’ve got three coordinate systems involved in one simple project – true State Plane, modified State Plane, and my own TRSUD system. Figuring out how to report geo-referenced coordinates and provide clear metadata is becoming a challenge. It’s got me to thinking it’s time for me to dump State Plane.
We’ve been working with a local system for our CAD work since we started with GPS in 2000. We use SPC for reporting the coordinates and then give clear metadata on how to go from our bearings to grid and our distances to grid. The only thing we actually use the SPC for is to convey where a point is. I’m thinking latitude and longitude can do it easier. My metadata could go from three paragraphs to three sentences with this sort of change.
In considering the pros and cons of SPC, I come up with this:
Pros
SPC is somewhat cryptic – it’s not preset on any smartphone or consumer GPS, making it tremendously difficult for a layperson to use.
SPC coordinates can be inversed with simple trigonometry whereas Lat Long requires higher order mathematics.
Translations and other coordinate manipulations to an SPC value are simpler.Cons
SPC is somewhat cryptic – not many people (including some surveyors) understand it and it’s limitations.
It’s easy to screw up. Lat and Long aren’t easy to scale or rotate like SPC.
SPC carries distortion baggage (high scale factors and large convergence angles).
Not commonly used. Most State resources (scanned quads, aerials, etc.) are provided in UTM.But before we change the way we’ve been reporting geo-referenced coordinates for the past decade and a half, I thought I’d solicit the opinions of the knowledgeable people here. What do you think? Should I report L/L for my surveys and skip the overhead of SPC, or is there a convincing reason to report SPC instead?
Norm replied 10 years, 4 months ago 10 Members · 22 Replies- 22 Replies
Sorry…
Lat/Lon/H (or maybe geocentric X/Y/Z) is my choice.
Nothing ambiguous about LLH (or XYZ for that matter), so long as you clarify the Datum and realization.
I’ve yet to see anybody SCALE, ROTATE, or otherwise “modify” Latitudes & Longitudes.
Loyal
talk me into H, Loyal.
We’ve been carrying elevations on every survey for about the past 6 years, but it’s for our own records. Why should I include H in my reporting of boundary monuments? Should I report to some precision (something that limits my exposure to liability)?
This is all kind of related to a couple threads over the last day or 2. I find this stuff terribly interesting. Yesterday’s discussion about projections took me back to a programming project I’ve been wanting to do for some time: distance between 2 L/Ls. The math is not easy at all.
SPCs of any flavor would be easy but doesn’t take into account any curvature.
I’m all for picking one single datum to report on. Problem with SPC is what was it based on? NAD27, 83 (and which epoch), etc.
L/Ls don’t have epochs and don’t change but as you all have said, they can’t be rotated or scaled. I don’t reckon they should either for that matter. 🙂Some number of years ago I wrote a program for LarryP to weed out certain point data from huge LiDAR point files. These were all SPC and was easy to locate points given 2 bounding corners. No problem. Then he wanted an option to convert those points to L/L on the fly. That was a whole ‘nother animal. It took me a couple days to figure out the math for that based on some docs he sent me from the NC geodetic folks. Turns out that depending on the point’s input L/L I had to lookup a scale factor from a table of a couple hundred entries. Talk about a CPU hog!!
That stuff was all using Lambert projections as it turns out.Back to your quandary: Are you planning on going back to convert previous projects’ datae (sp?) to your “new” standard or simply state that “from hereon all projects data are to be reported in xxxx datum”.
If the latter be the case, pick the commonly used and dump any of this “modified” or “local” stuff. Pick one, cast it in stone as the 11th commandment and don’t look back. And, if someone doesn’t want to play by your rules, smite them a mighty blow. 😀Note to self: don’t offer to write Shawn a conversion program lest I’ll have to learn all these other datums as well. :'(
> In considering the pros and cons of SPC, I come up with this:
> Pros
> SPC is somewhat cryptic – it’s not preset on any smartphone or consumer GPS, making it tremendously difficult for a layperson to use.
> SPC coordinates can be inversed with simple trigonometry whereas Lat Long requires higher order mathematics.
> Translations and other coordinate manipulations to an SPC value are simpler.and you forgot:
– The parameters of the Texas Coordinate System projections have been published as statute and so are hardly possible to confuse or mangle.
– Using standard projections makes comparison of data sets from different sources obivous and simple.
– Many surveying software programs already have them coded and identified by projection zone.
– Expressing positions as rectangular coordinates in the Texas Coordinate System facilitates checking and calculations from bearings and distances expressed in the same system.
– Magnitudes of discrepancies are readily seen. (Who really cares what the error in longitude or latitude is when the critical value is horizontal distance?)>
> Cons
> SPC is somewhat cryptic – not many people (including some surveyors) understand it and it’s limitations.Much less cryptic than a bastardized projection and definitely less crytic than LLH for most real world purposes (aside from use of a recreation-grade GPS receiver).
> It’s easy to screw up. Lat and Long aren’t easy to scale or rotate like SPC.
More importantly, you have to convert the LLH values to rectangular grid coordinates to efficiently check data entered as bearings and distances in that grid system.
> SPC carries distortion baggage (high scale factors and large convergence angles)
Actually, the mapping angle is not a distortion since angular relationships are preserved over typical land survey distances. The CSF typically changes very little over most land survey project, particularly when there is little terrain relief. When there is large relief, the scale at the surface will vary regardless of whether bastardized coordinates are used.
> Not commonly used. Most State resources (scanned quads, aerials, etc.) are provided in UTM.
Translation: “Not commonly used by GISers”. That’s a feature, not a bug. Most GIS software should have the ability to reproject Texas Coordinate System coordinate values.
> But before we change the way we’ve been reporting geo-referenced coordinates for the past decade and a half, I thought I’d solicit the opinions of the knowledgeable people here. What do you think?
Well, if the object is to make as much difficulty as possible for a surveyor wanting to use some survey product you generate and to facilitate its abuse by members of the public, I’d definitely switch to LLH.
talk me into H, Loyal.
I would say that Ellipsoid Height (H) could be problematical in some cases, which is why I tend to like Geocentric X/Y/Z (folks either understand THAT, or they DON’T).
The conversion from XYZ to LLH (although iterative) isn’t at all difficult, and the NGS Tool Kit has an interactive (XYZ-LLH & LLH-XYZ) program, as well as a downloadable program (XyzWin).
The reporting of “elevations” is not something that I would do UNLESS specifically required to do so (for the reason you stated), but an Ellipsoid Height (directly or indirectly via an XYZ), can be construed as another “clue” (footstep) in later retracements.
Obviously positions derived with a Total Station are another issue altogether when we start talking about “heights.”
I have recorded Geodetic positions BOTH ways depending on my mood over the years, and am still not convinced that one way is better than the other.
The last ROS that I recorded (last month), showed ONLY Latitude & Longitude, so I’m not going to try and convince you to go the next step.
Most of my work is usually Geodetic Control, so XYZ is a no-brainer on those.
Loyal
HEY SHAWN!
Please excuse the temp hijack, but Shawn I would like to ask you a couple questions, if you will email me at jtstrickland at bellsouth dot net, please.
thanks,
jtBoom!
State Plane Coordinates are Obsolete
Surveyors measure angles distances in a variety of configurations. We make maps from those measurements. Maps are 2-dimensional so we show horizontal in one view and vertical in a profile view.
Enter the digital revolution and 3-D digital spatial data. We still collect data and make maps although the logistics of data collection, data processing procedures, data storage,and product deliverables are much different. Yet we continue to force “new wine into old bottles.”
Map projections are strictly a 2-D mathematical model. But as a way of extending plane surveying techniques over longer distances, map projections have proved to be very valuable. To do that with greater integrity (smaller grid scale factors) the concepts of ground coordinates, project datum coordinates, and other “localization” procedures have been implemented by the vendors and many spatial data users.
Your arguments in favor of using SPC over the non-standard local systems have merit. But, I suggest that you are promoting continued use of an obsolete model.
The global spatial data model (GSDM) handles 3-D digital spatial data with no loss of geometrical integrity (no grid scale factors, no elevation factors, etc.) worldwide. Further more, a simple inverse between two GSDM points yields ground level horizontal distances and true azimuth with respect to the meridian through the standpoint. The mathematical formulations for the GSDM are much less complicated that map projection concepts and equations.
There are several obstacles:
1. We are not sufficiently familiar with the underlying geometry concepts to feel comfortable using the GSDM. This problem is correctable in education and seminars etc.
2. Vendors market and sell what customers request and, more importantly, will buy. The vendors continue to make money selling obsolete tools because that is what have been persuaded to buy. This problem is a huge professional and economic challenge. Any suggestions on how to surmount that obstacle?
3. Clients request deliverables that are compatible with existing computational systems and records. Maybe this is not an obstacle because we (the surveying profession) make money by listening carefully and providing what the client wants even if it means “going backwards” to meet there requests – after all, they are paying for it.
My goal is that as clients become more sophisticated in their requests for reliable 3-D digital spatial data that we (the surveying profession) will be right there with the efficient procedures and data that address the clients needs and requests. That will take a while and progress will not be uniform. But, I also hope that a sufficient number of surveyors will be well equipped to serve those clients effectively and profitably.
The 3-D Genie will never go back into the bottle so we had better learn to deal with it. See http://www.globalcogo.com
State Plane Coordinates are Obsolete
Prof Burkholder,
Could not agree with you more except to say that state plane coordinates have been obsolete for a long time.My first introduction to state plane coordinates was in about 1972. At that time, given most distances were measured with steel tapes, the accuracy of the system seemed pragmatic. However, electronic distance meters were beginning to be used by some surveyors. It didn’t take much understanding to realize there were going to be problems or confusion when one compared the parts per million of the distance meters with the one part in ten thousand for the state plane coordinate system.
The issue of distance meter and differences between ground and grid were insignificant in relation to the other. For the most part, few knew how to compute state plane coordinate and even fewer understood how the system worked. Drawings with erroneous scale factors appeared. Construction plans appeared with “modified state plane coordinates.” Some appeared with coordinate values for points with differing scale factors from others. Too, it was discovered that many used “3.2083,” a number with insufficient significant digits, to convert coordinate values between meters and feet. The problem was further compounded because many surveyors did not know the difference between feet and US survey feet. Those problems were carried on into state legislation with some states selecting meters, some feet and others US survey feet.
If one wishes to witness the scale factors fiasco, all that is needed is to do a search for the term on the BeerLeg web page. The evidence in the form of questions and responses indicates there is a lot of misunderstanding.
As it all turned out, when state plane coordinates were presented on some map or plan, it was not possible unless one knew the person or the methods employed, to know just exactly how the coordinates were determined. The only thing that one could assure in most cases was that there was going to be confusion. My experience indicates this continues.
As for GSDM, I am optimistic but also realistic. With the banner wavers proclaiming “the math doesn’t matter” and other such similar slogans, there will be problems implementing the GSDM. It will take a realization that surveying requires not just training, but understanding of legal concepts, measuring and mathematics and how they all work together. Supplementing this, it will be necessary for thinking and working to be done and visualized in three dimensions – in a world view.
Retiring the obsolete state plane coordinate systems as well as retiring old inefficient and ineffective methods, while retaining those methods that work, can only help those in the surveying field. As for clients becoming more sophisticated, I don’t have much optimism. Reality along with probability indicates sophistication stops when issues diminish their profits.
State Plane Coordinates are Alive and Well
> Retiring the obsolete state plane coordinate systems as well as retiring old inefficient and ineffective methods, while retaining those methods that work, can only help those in the surveying field.
I really don’t see how. The SPCS is an easy way to express geodetic positions at millimeter accuracy. The old objections to scale factors being hard to deal with has faded into history as most modern survey adjustment software (such as Star*Net, for example) implements a rigorous reduction to grid of distances measured at ground scale.
The only problem, such as it is, with the SPCS is that many of the drafting software designers have failed to implement simple mods to their software to accommodate the fact that the coordinate base of a drawing may be in some coordinate system that is related to drawing units by a scale factor. I use a truly ancient CAD program that has this extremely simple modification and can design in surface units on a coordinate base in the SPCS and likewise annotate in surface units (or any other unit, for that matter).
Lengths input for drawing entities are multiplied by the scale factor before being created in the drawing. Lengths queried in the drawing are divided by that same scale factor before being reported or annotated.
State Plane Coordinates are Alive and Well
YUP, this is he problem!
Lengths input for drawing entities are multiplied by the scale factor before being created in the drawing. Lengths queried in the drawing are divided by that same scale factor before being reported or annotated.
You don’t need to do that. Coupled with it being 2D in a 3D world it just turns into a continual mess (back and forth). Stick with it if you wish, the world is mostly moving on.
State Plane Coordinates are Alive and Well
> YUP, this is he problem!
Not really. Anyone who wants to use ECEF coordinates to specify the positions of boundary corners (which are 2D entities unless one is dealing with air rights such as airport approach surfaces or view easements) probably doesn’t understand how the SPCS functions in land surveying practice. ECEF coordinates are a solution in search of a problem for most land surveying purposes.
State Plane Coordinates are Alive and Well
Anyone who uses GPS uses ECEF coordinates, that’s the fundamental system. You need all three X, Y & Z to define a point on a projection. You can go to any projection from the ECEF 3D coordinate. Once you go to SPC without an accurate elevation you can’t get back to the fundamental ECEF, you have orphaned yourself from the geodetic system. Yes, you may get back to a lat and long, which is a line from the center of the system heading out into space and say your boundary point is where it intersects the surface of the earth. But, if you want to get back to the fundamental ECEF you’d need to go measure the ellipsoid height and back in which is only and estimate at best.
If you have the ECEF as the basic data and some modern software you are only a few clicks away from any coordinate system you may need. If all you have is SPC you don’t have that.
Why would I want to continually convert into and out of SPC and ground coordinates on a project. I used to do that, it was a pain loaded with problems. As soon as I found a better way I left SPC’s behind as a working tool. If I need to report SPC’s on a project no problem, my basic data and software can produce them in a snap.
Hey, I was going through some old stuff to day and came across my STARNET manual and software. It was a great tool in its day.
HEY SHAWN!
You’ve got mail.
State Plane Coordinates are Obsolete
Mr. Burkholder,
I respect your position on this and your passion for the topic. I’ve checked your website out before and there just wasn’t enough information regarding the GSDM for me to get on board. I’m not opposed to it nor for it, simply because I’m still not sure what it is.Perhaps I’ve missed the page that reveals what it’s all about…
> > In considering the pros and cons of SPC, I come up with this:
> > Pros
> > SPC is somewhat cryptic – it’s not preset on any smartphone or consumer GPS, making it tremendously difficult for a layperson to use.
> > SPC coordinates can be inversed with simple trigonometry whereas Lat Long requires higher order mathematics.
> > Translations and other coordinate manipulations to an SPC value are simpler.
>
> and you forgot:> – Expressing positions as rectangular coordinates in the Texas Coordinate System facilitates checking and calculations from bearings and distances expressed in the same system.
That’s the same thing I already stated regarding inverses and translations.
>
> >
> > Cons
> > SPC is somewhat cryptic – not many people (including some surveyors) understand it and it’s limitations.
>
> Much less cryptic than a bastardized projection and definitely less crytic than LLH for most real world purposes (aside from use of a recreation-grade GPS receiver).
>
> > It’s easy to screw up. Lat and Long aren’t easy to scale or rotate like SPC.
>
> More importantly, you have to convert the LLH values to rectangular grid coordinates to efficiently check data entered as bearings and distances in that grid system.
>
> > SPC carries distortion baggage (high scale factors and large convergence angles)
>
> Actually, the mapping angle is not a distortion since angular relationships are preserved over typical land survey distances. The CSF typically changes very little over most land survey project, particularly when there is little terrain relief. When there is large relief, the scale at the surface will vary regardless of whether bastardized coordinates are used.
>
You don’t consider a 2°-3° mapping angle from North to be a distortion? The fact that a CSF has to be considered at all is bothersome as evidenced by all of the techniques (proper and otherwise) which are employed to overcome them.>
> Well, if the object is to make as much difficulty as possible for a surveyor wanting to use some survey product you generate and to facilitate its abuse by members of the public, I’d definitely switch to LLH.If working with LL is too difficult for you then perhaps you should not be using GPS. Regarding abuses by the public, I’ve never been one to think we should be using secret decoder rings to assemble and disassemble survey data, which is basically what SPC is – a de facto secret system only used by surveyors (and often times poorly at that).
I didn’t post the question to convince you, Kent. You’re set in your old ways and that’s fine. I can follow your surveys, I’m sure. But if you think SPC is “alive and well” then you haven’t been paying attention, and I doubt I’m the one to edify you.
State Plane Coordinates are Obsolete
Shawn,
I should avoid promoting the book I wrote on this site but you should know:
1. Practially everything in the book is also posted on the Global COGO web page. But, the material is organized much better in the book than it is on the web site.
2. A simple Google of “3-D Global Spatial Data Model” will lead you to various places from which you can purchase the book.
As questions come up, I’ll be happy to answer any/all I can.
State Plane Coordinates are Alive and Well
Kent – with regard to boundary surveys, I invite you to read and understand a real live example which ends up with a 2-D plat (boundary survey) based on a 3-D GPS survey.
State Plane Coordinates are Alive and Well
> Once you go to SPC without an accurate elevation you can’t get back to the fundamental ECEF, you have orphaned yourself from the geodetic system.
The only missing piece is ellipsoid height and that is trivially easy to obtain for most land surveying purposes. You may have forgotten that even an error of 20 ft. in ellipsoid height won’t introduce a scale error more than 1ppm in the projected lengths of GPS vectors. Considering you’re probably mostly surveying fence posts in your end of Utah, that would introduce an error of only about 1.6mm over a mile when your RTK rover “shots” on the fence posts are probably decimeter level or worse.
In other words, I admire your desire to dress it all up as a work of science, but it doesn’t really make any sense as a work of land surveying when you consider how easy it is to independently derive an ellipsoid height that is much closer than 20 ft. to the actual value.
> > – Expressing positions as rectangular coordinates in the Texas Coordinate System facilitates checking and calculations from bearings and distances expressed in the same system.
>
> That’s the same thing I already stated regarding inverses and translations.Actually, not. If you think about how a surveyor would generate coordinates for a boundary with, say 200 courses, you’ll appreciate the merit of being able to compare coordinates directly after manual entry of the 400 calls and the nearly inevitable hunt for blunders.
While I just provide the coordinates of all the points in the Texas Coordinate System in OCR-legible form, I understand that many surveyors are uncomfortable reporting the coordinates of more than a few points. Those tend to be a time-waster to digitize.
> You don’t consider a 2°-3° mapping angle from North to be a distortion?
No, obviously not when the projection is conformal. If you’re worried about adjusting your compass, you should realize that you can adjust it to indicate grid North about as accurately as true North.
> The fact that a CSF has to be considered at all is bothersome as evidenced by all of the techniques (proper and otherwise) which are employed to overcome them.
So, it takes a land surveyor, does it? Okay, that’s obviously too difficult for the average lay person. :>
> I didn’t post the question to convince you, Kent.
No, I read it as a cry for help.
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