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@mightymoe I was a little intrigued so i read the first part if the pdf that Montana DOT puts out. I really like the way it is written. They speak about plane systems pros n cons. Geodetic systems pros n cons projected systems pros and cons. What I truly find interesting is that they seem to understand that one can do so many things on the State Plane Coordinate Systems without scaling coordinates. Even in the bridge layout they show how to take the distances if in ground from a set of plans and do the layout on state plane. And vice versa. Truly someone who understood was part of getting that going. Even the area they show. If on grid or on ground. I want to meet the person or persons who wrote that. It was to the point simple. At least the first portions I read this evening. Why I can’t get some to see this i have no idea. Somewhere someone with influence said something and did something and others followed and never understood I reckon. You could take thos first parts and do a very good curriculum out of those and already have the learning objectives etc.
@olemanriver I recently used one of their surveys to do a 280Ac tract with 28 monuments from 5 different surveys. This tract was basically surrounded by the 5 legals and is a remainder of an original parcel that’s been broken up over the years. The Highway was east of all the tracts but tied common Section corners so in theory the 5 legals could be pieced together and then the 28 monuments could be recovered. Not likely but….
The DOT survey was a metric era survey and it was interesting. The control shown is metric in state plane, distances for the drawing were shown as metric and feet. The metric distances are state plane, the feet distances are ground. Since the plans run north-south there are three Project scale factors so depending how far north-south you are you change the calculation.
I was able to tie the common corners of the 5 tracts to section corners shown on the DOT plans, calculate and rotate translate the 5 descriptions and drawings, put it all into a projected file since the DOT gave me the Lat, Long data needed, then occupy one control point on the DOT plan set and search for monuments. I found all of them within a few tenths of my calculations. Only one was off and it was clearly a witness corner since the corner would land in an irrigation ditch.
I haven’t looked much at any MDot manuals, I would imagine that they explain the three scale factors for that job. They range from 290PPM to 320PPM
Look for “Survey” near the top left of the page here:
https://www.mdt.mt.gov/publications/manuals.aspx
Current MDT Survey Manual Revision Date: May, 2005:
Chapter 2 clearly outlines the various things going on in Montana.
If 3 zones are preseent, then that project is likely in NAD27.
The Manual spends considerable text discussing the difference between NAD27 & NAD83, and the caution required to use the correct system. (2.2.2.2 Control Surveys – State Plane Coordinates)
Current Survey Guidance discusses Control is done in meters, and converted to Project Units:
https://www.mdt.mt.gov/other/webdata/external/cdb/SURVEY/MDT-Survey_Summary-Guidance.PDF
Surveying for Structures (Revision Date: August 2002):
https://www.mdt.mt.gov/other/webdata/external/bridge/structures-manual/part_II/chp-12-final.pdf
The DOT survey was a metric era survey and it was interesting. The control shown is metric in state plane, distances for the drawing were shown as metric and feet. The metric distances are state plane, the feet distances are ground. Since the plans run north-south there are three Project scale factors so depending how far north-south you are you change the calculation.
A prime example of where a project-specific low-distortion projection could solve a lot of problems and potential headaches.
Our DOT does the grid-ground scale-shift procedure something like every six miles along corridors, rather than just develop a couple of LDPs that would cover 50-70 miles (or more in some areas) each with a rigorous system requiring no messing with coordinates after the fact.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil Postman@rover83 Yes, but I will say those drawings are super easy to use. When I tie into them I don’t use the state plane numbers. I’m more interested in matching GLO/BLM original or dependent surveys, but the DOT data is valuable.
Converting it to my own LDP is a couple of seconds.
You can create a geographic north plat with actual ground distances but it won’t close using most programs
I’m confused, how does which North you choose for your bearing base affect the closure of the plat. You should be able to use magnetic, assumed, or geodetic and still have closure. You have a closed figure always and the only question is how it is rotated.
@lurker A sometimes poster here developed a geodetic program for the HP48 that we used way back when. It allowed you to traverse geodetically using conventional instruments without the mountain of calculations necessary before and convert lat, long to state plane coordinates. There was/is a BLM program that easily dealt with cadastral true north calculations, and Eric Burkholder mentioned above has programs for this very thing.
I was about to acquire the BLM version (I’m not sure what the acronym is) many years ago but then I got Trimble and it became a non-issue for me. Might as well use what you got.
There was/is a BLM program that easily dealt with cadastral true north calculations,
Geodetic COGO or GOGO, I think.
Used it in school, I was lucky enough to have one of the BLM developers of the program as instructor for my Cadastral Surveying course.
Cool program, most of the younger students didn’t like the MSDOS/command line entry.
“…people will come to love their oppression, to adore the technologies that undo their capacities to think.” -Neil PostmanEarl is a great guy, and passionate about geodesy and doing it right.
@rover83 I keep thinking it was called CMM, not sure why, I know Glen would remember.
Yes, great program. The command line interface took a bit of getting used to, but was very fast and straightforward. I tried to use it recently, but I couldn’t get it to play on my 64-bit machine. And Windows 10 doesn’t have a 32-bit simulator anymore. I’m pretty sad to lose the use of it. Far and away the best thing I’ve used for straightforward mean bearing comps.
CMM = Cadastral Measurement Management.
Kurt Wurm of New Mexico State University has provided Cadastral Measurement Management for Windows (WinCMM)
More than a decade ago I offered my opinion that the “problem” with state plane or any other coordinates was not that they were “distorted” in any way, but in the expectation that a simple planar inverse calculation would or should provide distances and bearings that match what is measured in the field.
With modern computing capabilities in everyone’s hands, it would not be difficult to use a more rigorous inverse calculation that considers the projection parameters and elevations of the points to provide average-elevation distances and mean true bearings.
This more-involved calculation would likely be done only for the lines that will actually be labeled with distances and bearings. For behind-the-scenes inversing for purposes such as terrain modeling and earthwork quantities the simple planar inverse would require less computing overhead and be plenty accurate.
It is believed that the Traverse PC software offers such capabilities.
GB
@rover83 I keep thinking it was called CMM, not sure why, I know Glen would remember.
Yes, great program. The command line interface took a bit of getting used to, but was very fast and straightforward. I tried to use it recently, but I couldn’t get it to play on my 64-bit machine. And Windows 10 doesn’t have a 32-bit simulator anymore. I’m pretty sad to lose the use of it. Far and away the best thing I’ve used for straightforward mean bearing comps.
I use Oracle’s free VM VirtualBox to be able to boot my smoking 64 bit Win 10 machine into Windows 7 Pro for apps that are valuable/powerful but aren’t being updated for prime time. Even if you’ve never set one up, the online instructions make it pretty easy. You do have to have the other OS license as well, though, but has been worth it for this use.
dd@glenn-borkenhagen
We can use this equipment to measure very accurately, then we shrink the measurements so they represent a surface thousands of feet below ground. All so someone can push a button with no thinking. The same type of global map projections that cause Greenland to appear bigger than Africa or South America.
Putting it on a 3D geodetic basis would make that go away.
But we got to get it down to pushing buttons or it’s not gonna happen.
Questions:
1. What is the least understood aspect of plane coordinates or plane coordinate systems?
How each data collector and office cogo/processing software deals with projections, corrections, frameworks, and their interactions.
2. What is the most error-prone aspect of using plane coordinates?
That few manufactures explain their approach in language that is consistent across the industry.
-All thoughts my own, except my typos and when I am wrong.Teaching search and rescue team members a bit about land navigation, the most misunderstood grid-related concepts I’ve encountered are
- Keeping the different systems straight: UTM, military grid reference system (MGRS), Civil Air Patrol grid, United States National Grid (USNG), and Vermont State Plane. The last is shown on some Fish and Wildlife maps of wildlife management areas, which are places where people might get lost, and where SAR teams might practice.
- Understanding it’s possible to mix and match grid systems with datums.
When I hear complaints about the inaccuracy of State Plane calculations, I usually formulate an outrageous example to answer them.
Today’s outrageous example is this: Use the North Carolina State Plane Coordinate system to calculate the length of Runway 05 at Helena, MT, Regional Airport.
The numbers are in the picture below. Runway lengths are slope distances while state plane calculated distances are horizontal distances at an average ellipsoidal height.
The runway end elevations are orthometric heights and I don’t know if they’re NAVD 88 or NGVD 27, but the two systems are very close, so I adjusted then to the ellipsoid with the Geoid 18 height of the airport’s PAC.
Anyway, the given slope distance is 4644 feet and the slope distance calculated from North Carolina State Plane Coordinates is 4643.989 feet.
You were saying about State Plane inaccuracies…?
Edit: The airport data are here: Airport Data and Information Portal (faa.gov)
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