Grid vs Ground Coordinates
Very well written. I could only add that so many make the mistake of when pulling the combined factor from a NGS data sheet that NGS always publishes ground to grid yet we all keep stating grid to ground. The combined factor is for scaling the ground distance to the grid distance.
Very very nicely written. However attached is a snippet of a NGS data sheet elev factor scale factor combined factor. I do wish they would reword the elev factor as it is in NAD83 at least ellipsoid. NAD27 elev at MSI
@bc-surveyor I liked your video just had a chance to watch it. A couple things. One the 1:10000 was not for grid and ground distance. That was for the state plane as we say to be 1;10000 to geodetic aka ellipsoid distance. It was documented that 1:10000 could be achieved if all other corrections were mad. Aka compute the CSF and apply that to the ground distance measured. Curvature and refraction. The corrected zenith angle before reducing the slope distance to a horizontal distance.
The 2nd thing I would add is bring in the topic of mapping scale as I have witnessed people confusing this with the scale factor itself. Not the same.
3rd NORTH
True north aka hardly no one uses this
Geodetic north nad83 non grid or nad27 non grid
Grid north when the geodetic north is the only place and all others are parallel which causes the deflection as we move east or west from the central meridian
Astro nominal north some assume that geodetic and true are all the same they are not
Of course magnetic north
And assumed north
This is where just like you stated when scaling coordinates META DATA is important That’s what tells us about the data I see nad83 only for a north arrow I know when it is on a plat it more than likely means grid north but meta data would make no doubts aka nad83 (2011) my state coordinate system and zone META DATA is important.
I grabbed a plat today magnetic north might I assume the surveyor actually sighted a line and recorded that and which date was it done or did he choose a bearing on a plat pre that stated mag north and a date . For the most part we care about being relative but that magnetic north could be the last hope if all but one monument was destroyed . One could use that and bring it all the way to today’s geodetic bearings or azimuth to grid within the tolerance of the models historically and the precision and care of how it was taken .
I honestly wish we would stop scaleing coordinates yes it works but scaling at one point creates a project coordinates system not a ground. Again even if we threw away the GNSS and went back to assuming 10000 5000 we are still working on a grid system or a plane. Just not a projection. We are actually working on multiple planes based on gravity and we must assume gravity is the same at every set up which when we are at the base of a mountain and go around it gravity is pulling us to center mass not the same direction. This is also proved from running geodetic levels as the direction of the line we run in can change yes ever so slightly our differences in heights.
I do enjoy videos and truly wish I had you ability to communicate so clearly and concisely. From and old man that is unedumacated. lol Great work. Keep teaching you are doing a great job.
Great subject and thanks for another well crafted video. Here in North Carolina, the birthplace of the State Plane Coordinate System, NC Grid is shorthand for the NCSPCS. My assumption is that when a name gets too long, such as the North Carolina State Plane Coordinate System North American Datum of 1983 Version 2011 Epoch 2010.00, it's going to get a nickname. Fortunately for us, NC Grid is mentioned in our GNSS and metadata regs (attached).
Naming conventions aside, I'd like to see more states require that at least one boundary corner be tied to their state's SPCS. While I have sympathy for older surveyors not wanting to invest in GNSS, I think the needs of the public, the profession, and the younger generation of surveyors outweigh the imagined hardships. I can understand how a PLS working in a state that hasn't had said requirement for over a decade might think it a burden or might imagine coordinates somehow replacing found physical monumentation. Well, fear not. I'm unaware of any PLSs that have reset an obliterated corner from a NC-Grid coordinate callout, but I suspect it would be a better option than proration if they did. We've been slapping GNSS coordinates on plats in NC for many years and it's made it easier to find irons and allowed us to provide better services to our clients. It even helps the GIS folks out at the tax department.
This old surveyor was including grid coordinates 24 years ago to aid in recovery.
This old surveyor was including grid coordinates 24 years ago to aid in recovery.
Never used to do anything with SPC. Purposely kept off of it.
Moved to a new firm, and this place is all SPC. They have records 30+ years old with SPC, and the break downs of sections, etc. It is very helpful.
It's interesting reviewing the statutes for this nomenclature; it looks like North Carolina recently updated the naming convention. I don't quite understand why 102.1.1 was repealed but they updated the statute effective 7-10-23. The statute states that the new name is to be the "North Carolina Coordinate System of 2022". It further defines 2022 with a location of the Lambert system and scale factor. However, later in the statute (102-1.2.) it states that for coordinates used in description or identification of surface area or location within this State the coordinates shall be identified as "NATRF2022" or "NAD83" or "NAD27".
I find the statute confusing.
Now, I'm no absolute defender of either NC statutes or procedures, but this one passes my personal muster.
Note that in prior state plane systems, Lambert projections were defined by a central parallel and two secant parallels, the north and south standard parallels. Changing the definition to a central parallel and scale factor is an improvement.
The new definition allows system designers to define the central parallel simply (without excessive decimal places) and also to set the accuracy (1:10000, for example) at the central parallel.
Under the old definition, north and south standard parallels were determined simply and the latitude of the central parallel was calculated. If you refer to Stem's publication 5, you will see the unwieldy result for the central parallel in NC.
The same reference will show that the resulting scale factor at the central parallel does not meet the 1:10000 criterion.
As to projection names vs coordinate descriptions, NAD doesn't correspond to rhe current name for the NC State Plane Corrdinate System, either. I suspect thar similar divergences appear in other states also.
In any event, Lambert projections can be defined by either defining standard parallels and computing the central parallel or by defining the central parallel, assigning a scale factor to it while ignoring the resulting standard parallels.
If you look at the Lambert zones in states like Iowa that have many LDPs, you will find that those zones are defined by central parallel and assigned scale factor. As an aside, all Lambert projections, including the current NC state plane projection, can be defined by a central parallel and its scale factor.
It's all just applied mathematics, and that's the easy part. The hard part is what surveyors do; use the resulting projections to produce a valuable product.
I'm only concerned about the naming convention. Are they wanting it to be named "North Carolina Coordinate System 2022" or the "North Carolina Coordinate System NATRF2022" or "NATRF2022". The first name seems to be the sweet spot, the second seems to be redundant, and the third doesn't give enough information.
The Montana code is more precise as it mandates the new name to be the "Montana plane coordinate system". The older systems are the "Montana coordinate system NAD83" and the "Montana coordinate system NAD27 (zone north, central or south)". I'm assuming from the new name 2022 is only going to have one zone like NAD83. Not a fan!!!
Overall, this is another great video. I would make a few comments.
First, you can almost always be certain that the metadata will be lost as soon as engineers or their ilk get their hands on it. I can not tell you how many times I seen plans based on my design surveys included in plan sets with none of the metadata attached.
Second, maybe I misunderstood what you were saying but you can most certainly derive a project combined scale factor from multiple locations within a project. This often provides a solution minimizing distortion over the entire project area. In a smaller area with minimal vertical relief a single point might work but not so much for larger projects.
It is best to scale about 0,0,0 and then truncate the resulting coordinate to ensure the resulting values are not confused with the grid values. See my first comment for reasoning. I have always disagreed with, the rational with scaling about a particular point to allow for inclusion of some data on an actual projection. I contend that you could just as well translate the data to fit the project coordinates, the distortions will be the same and when your values are released into the wild they will not be confused for something they are not. It makes even less sense now with CAD systems that let you specify how your project coordinates are transformed from projected grid values.
Remember, friends don't let friends scale grid coordinates without truncating.
