The knowledge needs to accessible to the typical user of the system. That means that the concepts need to be explained rigorously, but also boiled down to rules of thumb and best practices that can be remembered day to day in the field.
NGS manuals are a great thing, but the differences in jargon alone are a barrier to many.
My opinion is that the land survey industry through NSPS and such should develop best practices for implementation of these things in survey software, and provide certifications to software that is compliant. We do not use that sort of leverage very well in our profession.
@dmyhill you might just be onto something. Surveyors have kept to themselves and used various means to get things done through legal channels. I admire that. But sometimes ya just gotta speak up and say this needs to happen. NSPS might be a good place to start on something like that and work it from both ends. The NSPS and each states Association. But not even every state requires that a edm go to a established edm baseline either some states say manufacture calibration is fine. I have personally witnessed and used a few different total stations that passed manufacturers calibration but failed the edm baselines. When on failed we went to at least two other baselines to make sure it was not a fluke. I think you have a great idea. How to implement is something for discussion for sure.
I would say that your equipment merely converts lat/lon to state plane. There is absolutely no reason why it can't compute the SPC scale factor and the elevation factor.
It hasn't automated anything. It's just doing the same thing that a GIS would do.
I don't think so, and even if it did, that has nothing to do with its ability to compute the length of a line on the topographic surface.
The software's deliverable is a set of coordinates that have had random errors statistically removed. That is, if the software was used correctly and is not asked to remove systematic errors.
If those are present, then the job will fail one or more tests, and that shouldn't be ignored.
Yes, tapes and tables.
But James Stem's Manual 5 should have changed all of that. He gave us step by step instructions for converting lat/lon to state plane and calculating scale factors. His intent was for users to program those steps and eliminate the tables and the approximations that accompanied them.
Now the elevation factor is independent of the map projection, so Stem just gave an average radius for each state plane. Now, though, with GNSS, we know the ellipsoid height at any point and the radius for that point, so calculating the elevation factor should be easy.
So, I see no reason why surveying equipment can't deliver topographic distances and geodetic azimuths using state plane.
Questions:
1. What is the least understood aspect of plane coordinates or plane coordinate systems?
2. What is the most error-prone aspect of using plane coordinates?
1.) I would like to say it was something much more high level, but for me personally it was probably the shift when scaling from 0,0 versus a local coordinate.
2.) Scaling to or from grid seems like the obvious answer to this one.
@mightymoe hey it was prior to the year 2000 when i was on a survey crew in the PLSS arena. I do still have a BLM manual but only cracked it to refresh my brain on some computations like double proportions and the layout of the sections as i prepped for the FS exam. I did look at tge where the error was placed in sections etc as well. I need to dive in much more for PS exam i am sure. But my mind is blurry a little help me clear up something. Wasn’t the plss placed on true bearings so astronomical not geodetic originally? And one needed to understand the forward azimuth and reverse azimuth differences. Especially running east to west because its not orthogonal. Or am i way off. I was thinking about this and said to myself this could be a test question On PS exam i am preparing for. So the plss system did intergrated a plane and geodetic system originally together because of the large areas to be covered. I might have this all wrong in my head. Also the distance via chains were along the surface but horizontal except where steep slopes like around mine surveys. And acreage sometimes were along the slope of surface instead of horizontal. Like i said been a long time.
The PLSS is based on Astronomic bearings.
If you can find an area where the difference was measured accurately enough between 1800-1950 during the great surveys that you can see the difference between astronomic and geodetic bearings please let me know.
I'm following a 1884 survey and their astro bearing matched my geo bearings less than one minute. I figure I'm golden.
And yes a east-west bearing will be different than a west-east bearing along the same line.
Actually my DC gives Grid, Ground, Ellipsoid distances at any time, a simple pull down arrow to switch between them.
How does it compute ground? And what does grid mean?
@mightymoe well thank you. Not a lot of difference in geodetic and astronomical anyway. But if i was within a minute i would say they were all over it especially since they had equipment that they had back then. Most definitely thise surveyors that did good work back then had the definition of discipline to do what it took to get the job done correctly for sure.
When i use to use the magnetic compass on the old lietze the little tube one as a check to the solar observation to sun on rural surveys as azimuth check and i could be within a minute i knew my comps and angles were good enough.
thank you. I owe you one as now I know i will not miss that question on a exam. Lol. It has been dug up and dusted off in the brain.
I'd argue that the conceptual knowledge is absolutely accessible to any user of these systems nowadays. There are dozens of references and textbooks on surveying, geodesy, GNSS, GIS, remote sensing, etc. Plus plenty of online courses, and of course formal education from colleges and universities. If someone really wants to understand their gear, they've got the opportunity.
Whether services and deliverables are professional or not has little to do with the gear and everything to do with the user.
(A comprehensive formal education should not be optional for licensed professionals, but that's another argument for another time.)
NGS has put out a ton of guidance on best practices. Their presentation and publication libraries are chock full of technical reports about how to employ foundational concepts with the equipment and software available. Their webinars range from introductory to advanced, and allow users to ask questions in real-time if they are unclear on items covered.
There are also quite a few research papers put out by universities, public sector organizations, manufacturers, and private sector groups which delve into real-world scenarios testing out various methods and equipment. (On that note, most of the flagship manufacturers have plenty of resources concerning how their gear and software operate. Every now and again I run into something I don't understand, but that's usually solved with some investigation or a query sent through the dealer to the manufacturer.)
There's always going to be debate about how to modify or improve practices; we are supposed to be keeping up with these things as professionals. The day all our work can be summed up in a single checklist that never changes again is the day I hand in my license.
And to be brutally honest, if a user cannot understand NGS terminology, they're probably not ready to make professional-level decisions about how to employ their equipment or software.
In my experience, many folks, licensed or otherwise, consider such advanced learning to be a waste of time.
"This gear sucks! Which button do I press to make a survey?"
Grid is the projected surface. An inverse between coordinate pairs.
How does it calculate ground? You want the code for the program?
Please, no, not the code. I passed the million line parsing mark many years ago.
If the grid is state plane, then to get to ground distance, your equipment has to calculate two scale factors, two elevation factors and average correctly the two combined factors that result.
See, there should be no distortion problems if the process has truly been automated.
If the grid is state plane, then to get to ground distance, your equipment has to calculate two scale factors, two elevation factors and average correctly the two combined factors that result.
Trimble, for its part, is pretty clear about how it calculates ground:
Ive been using field software that computes CSF for at least 15 or 20 years. We used it to input NGS control points and check the result with the data sheet CSF. It also computes ground inverse that agrees with NGS tools.
Aha! So, Trimble is dividing the ellipsoid distance by an elevation factor, which it gets from the ellipsoid height.
It dosen't need grid to do that and that's pretty slick. But in cases where there is a grid, say state plane, what does it do?
@rover83 you can lead a horse to water but ya can’t make him drink. I believe your statement sums up a good defense of a tiered license system. At one time you could be a boundary surveyor or a geodetic surveyor in South Carolina. I guess you could be both. The problem is no one person can do it all. I have not advocated for this as I have always wanted to believe that the professional would not practice where one was not competent. But while I believe this i do not see it evident either in the day today workings always. I still say the majority does practice within the competency they have. I keep telling myself this. I have no doubt the knowledge is readily available NGS does have a massive library and videos. I go back to the old ones about datums and such and send those links to my crew chiefs and anyone who wants to learn or getting ready for the FS exam. The problem is the ones who are licensed already that have not mastered those particular concepts themselves I find have a attitude that is pushed down to those who are up and coming that many times those people then look at me and say things like well we don’t worry about that and it doesn’t matter for what we do. But you could literally watch about 3 videos from NGS and get. Easily 90 % of the questions asked on a FS exam related to GIS datums geodetic type questions correct. Me i want boundary knowledge and that is harder to gain than the datum’s because we work now in a way that mentorship is weaker and it’s about the bottom dollar. So i just keep rear asking questions until my boss runs me out of the office lol. He is a good boss i am just trying to gain all the knowledge i can as fast as i can.
I'll save you from the code. LOL
Rover's diagram gives an overview, however, the state plane grid is always shorter (lower) than
the ellipsoid height where I work.
This explains the Helena runway.
Of course we've always had grid and ground dimensions. Obviously back in the instrument days and always going forward. The problem is CAD programs don't work easily mixing the two. Labeling distances has always been a coordinate inverse.
Most of my work (subdivisions, small boundaries, DOT) is SPC bearings and ground distances within about 5PPM.
It dosen't need grid to do that and that's pretty slick. But in cases where there is a grid, say state plane, what does it do?
Same routine, actually. The user can set the default to whatever they like (grid/ground/ellipsoid), but it is easily switched on the fly when in a job. It's also shown in parentheses during inverses so the user is aware of what is being displayed.
So it really doesn't matter what is chosen for a coordinate system. If a project-wide scale factor has been applied to the job, the ground and grid distances should be darn near the same. If we're running in straight grid, we can see the difference by just switching and reviewing.
I can select two points, choose "compute inverse", and then when the inverse screen pops up I can go to an Options button at bottom and switch the distance display:
