I thought about ground but then decided to restrict the discussion to pure mathematical surfaces. The Elevation Factor is a ratio, but its denominator can't be computed without knowing the ellipsoidal height, a non-computable number.
@mightymoe do you place geodetic north on surveys or grid north where you are located.
Mostly it's State Coordinate System bearings and "surface" distances with a scale factor.
It's rare that anyone gets coordinate data. That's normally reserved for our engineering clients who are on-board with coordinate system design.
For a remote township type work I usually design an LDP. As always it depends on the situation. One recent project I did a COS with the origin point shown on the plat. The reviewer got upset that the point wasn't set and wanted it erased. So I did. I listed the origin point by LAT, LONG in the notes with projection parameters so anyone can get on the bearings.
Two ranch units I surveyed recently were very close to the CM so it made sense to use State Coordinate bearings for them. I really don't like being widely rotated from record simply to be on State Coordinate bearings.
As you have experienced, its possible to design an LDP to fit the need. It's unfortunate if SPCS2022 doesn't meet the need. The point is that it is possible to get users singing to the same sheet of music with some coordination.
It seems as if the people most likely to criticize SPC/LDP are often times the ones that confuse everything about geodesy in the first place.
For sure.
I don't even care too much about whether someone used this projection or that, as long as it's just a projection. Not a projection developed by starting with a projection that has unacceptable distortion, then screwing with coordinates and back-calculating a totally new one that is kinda-sorta-but-not-really like the original.
If you mess with a projection, it's not that projection any more. Don't pretend that it is. Develop a better one if you need to.
Additionally, a lot of reverse-engineered "SPCS ground projections" are rarely evaluated in the context of the entire project, or from a larger area within which the project is located. It's common to select a random control point for CSF calculations ("we have to get the CSF from OPUS!" is something I hear often) that is not optimized for the project itself - just for one or more control points which may or may not be representative of the extent and elevation change across the project area.
Mostly it's State Coordinate System bearings and "surface" distances with a scale factor.
engineering clients who are on-board with coordinate system design.
I usually design an LDP.
I listed the origin point by LAT, LONG in the notes with projection parameters so anyone can get on the bearings.
it made sense to use State Coordinate bearings
I really don't like being widely rotated from record simply to be on State Coordinate bearings.
FOR THE LOVE OF CHRIST, none of these things are consistent, or sensical?!
How much damage are you actually doing on a regular basis?
Here's a neat website from a great resource Ive met and interacted with a long my path.
Was a huge lift for my bigger understanding of the topic.
enjoy!
I would love to use that sort of system. Local horizon system using a simple rotation matrix is even easier to model than a projection.
I don't think even the survey world is ready for that yet. Much to be hashed out regarding geoid vs ellipsoid height, and at the very least I can't think of any standard commercial survey or CAD package that supports such a system. Wouldn't be that hard to implement though.
Earl Burkholder, Mr. Global Cogo, used to participate here but it's been 8 years since he posted. Do you know if he is still active?
I email with him every so often, he was the president of the SRG chapter of the NMPS when I was living in Las Cruces.
He's retired but still engaged in the world of geodesy and definitely alive and kicking.
@rover83 Earl used to post here. I haven't seen anything from him in a while.
He was instrumental in helping build the LDP we used at City of Las Cruces, and I posted the links here a while ago, not sure if they're still live or if they rolled them back and discontinued the process. Would make sense, I worked there and knew of people opinions on why it was a waste of time etc.... like yeah, why would we want to move into the future of the NSRS and be completely onboard with promoting the best possible practice....
I was only a user and working on digesting the bigger portion of what it took to develop and it's implementation.
I would love to use that sort of system. Local horizon system using a simple rotation matrix is even easier to model than a projection.
I don't think even the survey world is ready for that yet. Much to be hashed out regarding geoid vs ellipsoid height, and at the very least I can't think of any standard commercial survey or CAD package that supports such a system. Wouldn't be that hard to implement though.
It's doable with programs available, the problem of course is getting others on-board. You can create a geographic north plat with actual ground distances but it won't close using most programs and regulators will reject them. Plus, with any significant elevation changes all points will need to be 3D to make it work. But, it's the real future of coordinate geometry.
@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.
