This is old stuff ... nuttin' new
This is the same philosophy for local coordinate systems used in Michigan & Minnesota as well as the Republic of Colombia and lots of places throughout the world.
Biggest problem with this sort of arrangement is the communication between the field surveyor and the office GIS technician.
"Your field survey is wrong because it doesn't match my computer's data set."
Check out my Grids and Datums column on Columbia at www.ASPRS.org from November 1997.
It isn't magic, though
Never did have a high opinion of a state wide or national grid system. Sounds nice if you are into math or tend to want to centralize everything we do in life. Cogo uses a rectangular grid system so we all use a gride in our evaluation of evidence, we have made measurements on the surface for years and it works for our local needs. What the underlying goal of the SPCS is, is to make it possible to eventually survey everything from a central office and then send someone out to monument the results. As our technology advances we are finding out how much of a living and moving planet we live on and how that a fixed location on the surface does not exist. Like it on not, most of our surveys are local things and local control is what is important. LDP is part of the early maturing and return to local control for most of the surveying that effects most of the population, that should not have any effect or control the methods on those in need of large grids for management purposes where those types of projections are needed and conversely that need should never impose its methods and needs on the local work that most of us do. We need to stop the foolishness of fooling ourselves, get out on the ground and make our local measurement on the surface we live on and return our survey results based only on local evidence, that is the only evidence that will remain stable over time other than some unpredictable exceptions.
jud
Kent
I think I'll pass on using Montana coordinates in a legal (unless for some reason when a client requests it). Either reporting them or using them to calculate the description. When you reduce the surface distances by .7' per 1000' it just causes too many problems.
Kent
> I think I'll pass on using Montana coordinates in a legal (unless for some reason when a client requests it). Either reporting them or using them to calculate the description. When you reduce the surface distances by .7' per 1000' it just causes too many problems.
Why on earth don't you apply an average combined scale factor to the grid inverse? The coordinates take you to the point on the ground.
It isn't magic, though
> What the underlying goal of the SPCS is, is to make it possible to eventually survey everything from a central office and then send someone out to monument the results.
That's the first time I've heard that one! 🙂
It isn't magic, though
Think about it a bit. When we started using SPC in 73, that was one of the benefits we thought would make us money, once tied, never visit again. People and the tendency to use shortcuts has not changed.
jud
Some State Plane History
For those interested in the history of the SPCS, here are a couple of links to the NGS publications library.
This document by O.S. Adams dated January 1937, is about the earliest overview of the history and origin of the State Plane Coordinate System:
http://www.ngs.noaa.gov/PUBS_LIB/StatePlaneCoordinates1937.pdf
And also of interest, would be this one by Hugh C. Mitchell in 1950
http://www.ngs.noaa.gov/PUBS_LIB/StatePlaneCoordinatesInRouteSurveying_CGS.pdf
As you will see in reading these documents, ENGINEERS where (and are) the real force behind State Plane Coordinates.
Loyal
It isn't magic, though
> Think about it a bit. When we started using SPC in 73, that was one of the benefits we thought would make us money, once tied, never visit again.
Well, once you've run an accurate connection between section corners, do you repeat it in all subsequent work? If the tie is good enough, any discrepancies will only show that the monuments aren't stable, right?
Some State Plane History
> As you will see in reading these documents, ENGINEERS where (and are) the real force behind State Plane Coordinates.
Isn't it ironic that land surveyors now seem to be the only professionals able to actually *use* the SPCS and that the engineers generally prefer Kluge Koordinates for their projects?
Some State Plane History
Well Kent...if you had actually READ the above documents, you would realize that State Plane Coordinates were (and are) the ORIGINAL "Kluge Koordinates."
🙂
Loyal
Some State Plane History
> Well Kent...if you had actually READ the above documents, you would realize that State Plane Coordinates were (and are) the ORIGINAL "Kluge Koordinates."
I think you're forgetting how difficult it once was to measure distances with steel tapes at accuracies better than 1:10,000 in ordinary work. :>
Kent
Well, I do use a combined factor to calculate surface distances. I will not however, survey on the surface, project coordinates down to sea level, multiply inversed distances at sea level by the combined factor to arrive at a surface distance, if that's what you're saying. Just more work than I wish to do. I think I'll just to continue to work in surface coordinates and inverse surface distances. But I think we just work in very different areas. If I worked where the SPC distortions are small I would be using them also. I almost never do any work in a SPC system, nor do most clients want me too. There are a few who do. And I will gladly do so for them.
Some State Plane History
No Kent...
I think that YOU are forgetting that 1:10,000 went the way of the Dodo Bird back in the early 70s!
🙂
Loyal
Kent
> Well, I do use a combined factor to calculate surface distances. I will not however, survey on the surface, project coordinates down to sea level, multiply inversed distances at sea level by the combined factor to arrive at a surface distance, if that's what you're saying.
Yes, that's what we do. It's effortless to do the reduction of GPS vectors and conventional measurements in the survey adjustment process. Star*Net-Pro makes that a trivial exercise, for example.
Then it's just a matter of picking a good average combined scale factor for the project to be automatically applied when inverses are calculated and maps are annotated.
> Just more work than I wish to do. I think I'll just to continue to work in surface coordinates and inverse surface distances. But I think we just work in very different areas. If I worked where the SPC distortions are small I would be using them also.
Well, I've worked up to around 7,000 ft. in the mountains of West Texas and have never seen a problem with the method I've described, even though the scale distortions were close to 300 ppm. (about 1.6 ft. per mile). The SPCS values deliver the accurate *position* of the corner or monument and the surface distances will generally be closer to what one would measure at the surface than the so-called Low Distortion Projections optimized for the flats and valleys will.
Some State Plane History
> I think that YOU are forgetting that 1:10,000 went the way of the Dodo Bird back in the early 70s!
Well, that's certainly not the limiting accuracy of the SPCS. As long as you're within the limits of the projection zone millimeter accuracy is entirely possible. My point is that the Kluge Koordinate systems such as the Less Distorted Projections simply carry the same engineering philosophy forward, i.e. "Why worry about systematic errors of 20 ppm (1:50,000)?", that generated other projections in the era of steel tape and transit measurements.
Jud
I disagree. Sure, you want to check the monument is there but why re-run the line?
Personally, I love the grid. Working in the oil patch and using OPUS is the cats meow for tying different projects together and keeping the network tight from the word go.
Even without GPS, all large projects that were more than the run-of-the-mill boundary were tied to NAD 27 or NAD 83.
I can't count how many times by working on one side, then the other, that I've filled in holes and know where the lines are. Seeing the BIG PICTURE is one thing that SPC really helps and you end up with enough data to satisfy that old addage I was told years ago
"The difference in a bad decision and a mediocre decision is data. There are no good decisions".
Then it followed with
"You don't have to be a good surveyor if you find all the corners."
SPC have allowed me to do both with better and faster results.
Some State Plane History
It sounds like I view things a bit differently than you do...
I don't view an LDP as a "kludge". As a Surveyor, when you are using an LDP, you are perfectly free to use your floating scale factor, just as you would in State Plane or UTM, and maintain your millimeter accuracy.
The difference is that, when using an LDP, you can typically label all distances in your project with grid distances, and they'll be essentially the same as ground distances over your entire project. That tends to be a lot less confusing to all the non-Surveyors involved with the project. In effect, you can get your accuracy, yet eliminate "grid to ground" confusion among the non-Surveyors.
Some State Plane History
> The difference is that, when using an LDP, you can typically label all distances in your project with grid distances, and they'll be essentially the same as ground distances over your entire project.
Yes, but thats exactly what you get using the SPCS by applying a combined scale factor to annotate the surface distances. The exception probably being that the surface distances obtained by scaling the grid distances in SPCS will likely be more accurate than in the LDP where the combined scale factor is being ignored. The reason, of course is that the combined scale factor is optimized for a smaller area than a projection zone at county scale or larger.
> That tends to be a lot less confusing to all the non-Surveyors involved with the project. In effect, you can get your accuracy, yet eliminate "grid to ground" confusion among the non-Surveyors.
Yes, I think that the obvious appeal of the LDP is to enable engineers to design stuff in CAD. As was pointed out much earlier in this thread, it would be a non-existent problem if the drafting and design software companies had ever really gotten serious about incorporating scale factor functions into their products.
Some State Plane History
And as I said above, I think you may be overestimating the ability of hardware to do that... We often spend a lot of time waiting on our software as it is. If we forced every calculation to be done in an ECEF system, it would dramatically increase processing time, and slow down our software considerably from its current state. The day may rapidly be approaching when we could have such software, but I'm not convinced it's here yet.
Grid projections offer a nice intermediary. They allow us to operate in the "2-1/2 D" paradigm that is far more useful than an ECEF system, yet minimize the distortion, and do it all with relatively simple mathematics that doesn't bog down our design software.
Some State Plane History
> Grid projections offer a nice intermediary. They allow us to operate in the "2-1/2 D" paradigm that is far more useful than an ECEF system, yet minimize the distortion, and do it all with relatively simple mathematics that doesn't bog down our design software.
Oh, I'm definitely *not* arguing in favor of designing stuff in ECEF. That would be someone from Utah or Nevada who will take that end of the discussion. The point I was making is that just a simple function that scales distance inputs by CSF and likewise scales annotations and areas pretty much solves the grid-to-ground problem alleged to exist. That is, the drawing is constructed with an SPCS base and you can design a 100 x 200 ft. structure by inputting the dimensions 100 x 200 ft., but which are multiplied by the CSF to reduce them to grid. When the structure is dimensioned, the grid dimension is divided by the exact same CSF and .. voila!.
As for COGO, just the elementary function to specify the scale factor that is applied to distances input and output pretty much solves the problem for calculations once the GPS vectors and conventional measurements have been rigorously reduced to derive the SPCS values of control points and survey markers.
