Is there a book out there on projections, coord systems, related stuff, types of coord systems etc?
I've tied into some work performed by one of the big engineering firms locally. Basis of bearings is stated to be State Plane Grid North. Nope. It's geodetic, without saying where their base was. Or what theta to apply.
And, another job more recently. Theta has been applied twice. So, the bearings are not on geodetic, but are twice theta from geodetic, and once theta from grid.
Now, I know I don't know it all. But, I'm seeing a genuine need for a book that is in plain language, simple enough for me to understand,, and complex enough to accomplish the task of a normal modern surveyor.
Thank you,
Nate
This free download should help with some of that.
http://www.ejsurveying.com/uploads/2/5/6/6/25668328/working_with_grid_coord.pdf
I haven't found one, Nate. What I find is that they look promising until we get to the question that I want answered. Then they either stop or enter into their own world which is often irrelevant and sometimes plain wrong.
For example, this otherwise excellent old guide to Virginia DOT surveys gets very close in sections 10.08 through 10.10. but then it just quits and veers off into monkeyed-up state plane coordinates.
An indication to the real source of problems like the ones created by your engineer friends may be found in this GIS exchange. Just compare the myriad paths described and recommended and compare those to GPS points collected and then black-boxed into state plane coordinates in survey software. There may really be two issues: 1) understanding coordinate systems and 2) understanding software.
You've mastered these relationships well. Whatever you did to identify the problem is a key learning objective for those who haven't and should be part of the workflow.
How did you do that?
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USGS Professional Paper 1395
GPS for Land Surveyors , by Jan van Sickle
Yep, this is the one.?ÿ Might seem intimidating at first, but give it a minute.?ÿ Very straightforward and, as it says, a true "working manual".
And for old, grey-haired pharts like us, there is the earlier publication, "Map projections used by the U.S. Geological Survey," Bulletin 1532, 1982, also by John Parr Snyder.
I wrote more than a few FORTRAN programs using those two USGS pubs in the 1980s and early 1990s. 🙂
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Whatever you did to identify the problem is a key learning objective for those who haven't and should be part of the workflow.
How did you do that?
The blunt answer makes me look smart, but that's not real fair. There was a fair amount of "reasonable guesswork" applied.
I took the nomenclature "true north", and saw the lines drawn on a globe, that converge at the poles of the earth.
And, I saw the term "Grid" in grid north, and saw non-converging lines.?ÿ
Overlaying these 2, I saw theta, or convergence.
Then, I struggled mentally with these 2 superimposed images, and realized we are shifting the "backsite", not the "foresite".
Thus, a grid bearing will have a higher azimuth number, if I'm west of the central meridian, (which is where "true" or geodetic bearings are the same). Than a true bearing.
Laplace correction was not significant, for my purpose, as my instrument was not that caliber.
So, I've been using grid bearings, with solar observations, for well over 35 years.
My sun shot software allowed me to compute sunshot, with both grid brgs and geodetic brgs.
But, even before I had that, I used to compute sunshots, with scaled lat longs from a USGS. quad sheet. I'd artificially do the shots twice, once where I'd taken it, and once at a place 1 mile east, or west, to approximate convergence. This way, I could run an open traverse, and close the angles against the sunshots. This gave me specific convergence, for that area, or lat/lon.
My little brother was taking the ICS (International Correspondence Course) at the time. We used to talk alot. He taught me those big words, like theta, and how to break down section 5, 6 and 7, (when I could not remember what dad had taught me.) Also, Single Proportionate Measure, and Double Proportionate Measure. (SPM, & DPM).
So, when I first got RTK GPS, I bought a used Topcon Legacy E for 25k. I brought it home from Blue Eye Missouri. I took it to another surveyor, (TDS data collector), and asked how to get it to generate GROUND SCALE and GRID BRGS. It could not do this directly. It was a 2 step process. Set it all up, ground scale, and geodetic at the base. Then, go look up convergence, then go reset the prev system, with theta applied.
This I suspect is where most surveyors missed the issue. So, this other surveyor immediately replied "Is this why when I move my base, and back shoot, to my previous base, that there is a little rotational problem?" Well, we went over it, until we both learned. I learned how to do this in the data collector, and he learned the same, and why algebraicly subtracting the geodetic brgs, gave convergence difference.
Well, before this, I'd been using LOCUS GPS. These were 8 channel, L1 only units, that had algorithms to use the lowest sats in the sky.
So, I had tons of jobs, on grid brgs, ground scale. This was why I needed my legacy e system to address this.
Anyway, I'm no genius. I'm intensely practical, and useful, to equip others, (sometimes) by skipping alot of sidetracks.
IF I can once visualize and learn, I can often help others, by skipping alot of peripheral stuff.
Anyway, I'm now a Javad user, as their approach is a real neat screen, that allows all kinds of controll over the way this issue is handled. Not to mention it's ability to flush out genuine data, in rough places for GPS.
So, that's my story, of how I got this way.
Time to wake the kids.
Nate
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That's how I learn except that I go from the algebraic to the graphical and back again until what I calculate and what I see match. Sometimes I'm figuring wrong and sometimes I'm seeing wrong, but I keep at it until they come together. It's a labor intensive, time-consuming process.
The essence of understanding lies in how you know that your work is right or wrong, and that's what's missing from so many books. If the book began its discussion with this, for example, "When I can calculate the published bearing from one point to another using trig and Northings and Eastings, then the basis of bearings is grid. Here's why that is true." And then proceed to explain the coordinate system.
In teaching math, I saw that I often lost students during long explanations of theory followed by the application. They were worn out before we got to the purpose. Many times, reversing the order provided relevance and helped hold students' interest. It also helped them think about what the theory was providing.
Nowadays, though, we really have to know how to make field observations and graphical presentations match up. That adds another layer to teaching and learning.?ÿ
The more we simplify, the more complicated things get and the harder it gets to get things right.
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Some students, it's better to present the problem first, then the math.
Academics tend to present the math.../theory first.
If you present the problem first, then it builds a shelf in my brain first. If you present the math first, then I have a scattered pile of disorganised facts.
Some people can do either, or both. I prefer shelves first.
Thanks,
Nate
Is there a book out there on projections, coord systems, related stuff, types of coord systems etc?
I've tied into some work performed by one of the big engineering firms locally. Basis of bearings is stated to be State Plane Grid North. Nope. It's geodetic, without saying where their base was. Or what theta to apply.
And, another job more recently. Theta has been applied twice. So, the bearings are not on geodetic, but are twice theta from geodetic, and once theta from grid.
Now, I know I don't know it all. But, I'm seeing a genuine need for a book that is in plain language, simple enough for me to understand,, and complex enough to accomplish the task of a normal modern surveyor.
Thank you,
Nate
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I agree with Mr. Mayer. Van Sickle has been great reference throughout my career.?ÿ
Also check out "Datums" section in Caltrans Survey Manual found in the link below.
Hope this is helpful.
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http://dot.ca.gov/programs/right of way/surveys-manual-and-interim-guidelines
-Justin
If you are looking for a Handbook type publication, this is quicker and easier to reference than any of my textbooks on projections, SPC or convergence.
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@gene-kooper Yup...got that one too. I have used PP-1395 so much that it's held together with Duck Tape (or duct tape, whatever).
If you can get your hands on one of the old NAD27 books for your state, those are full of information explaining how to. Working through "hand" calculations from field observations to geodetic conversions.?ÿ
Nothing beats doing it with pen and paper.?ÿ
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I find it amazing how many excursions into 1980's era government publications people are wiling to do to avoid spending $73.02.?ÿ ?ÿ
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