State Plane Coordinates

right on. right on.

I don't use SPC, so maybe my opinion doesn't matter.

As to SPC coords, they are kinda like pregnancy -- either you is or you ain't.

As to why? the usual answer - lack of education and the motivation to get more educated. Too often the excuse (for this and other issues) is "that is the way it is done 'round here".

Stir away.

What about when a regulatory agency requires modification?

Link

Never did like the note on a Survey Drawing saying, "Ground Distances, Grid Bearings". Did they forgot a large part of grid to ground or is it addressed elsewhere?
jud

Loyal: I do not even consider bastardized SPC to merit the name of state plane. Just causes confusion. So, to me there is only one kind.

Good question z138, the answer to which is obvious.

DOTs (in general) are notorious for screwing with SPCs, and that's unlikely to change anytime soon. Some DOTs have moved out of the dark ages, some have not.

Loyal

John,

I (obviously) agree with you.

Loyal

I agree "State Plane Ground Coordinates" is not a good name. That goes for the procedure too.

Jud - The NJDOT Survey Manual does discuss Grid Correction but the manual does not seem to have been updated since the "Corrective Action".

NJDOT Survey Manual

Loyal,

I will probably get in deep doo-doo for this, but from my personal experience, the answer to "Why?" is that someone is trying to impress either his boss or his client, neither of whom have any clearer idea that he does.

I have known of companies that asked the question, "Do you want that on state plane?"

If answered affirmatively, the price goes up.

Besides, isn't more numbers, better? LOL

Geezer

Loyal, I just emailed you for clarification. I get confused a bit on what it is you don't like. I'm probably one of the doofuses that do it wrong.

I'm paranoid about using State Plane Coordinates only, because often times someone that doesn't understand SPC uses them to inverse direct distances that might not match the distances on their legal descriptions, or what they measure in the field.

anyway, thanks for posting on this issue. We need some of you real smart guys keeping us all in line.
Tom

The DOT's I work with all require "modified" state plane. The state plane coordinate is mulitiplied by an adjustment factor and creates a "surface coordinate". I've been working on those kind of projects since the 70's and don't have a problem with them. There is a lot of good control out there established from DOT projects and it's a good idea to use the information when it's available.

Since I started using GPS I really don't care about the coordinates. For almost all of my projects no one ever sees my coordinates anyway and when they do need coordinates I let them pick what kind they want and explain the options. I can only think of two clients that wanted actual state plane in the last 25 years and it made sense for one of them since what they do is pretty rough and it isn't going to get tighter for safety reasons so subtracting the distance error in state plane isn't going to effect their final numbers, but for the other client it was a mess doing that project in state plane.

I recently finished up a project that I had put on my own projection and surface coordinates. Two months later I got a call from a GIS guy who couldn't understand how to put it on the "grid". Of course I asked "what grid? It's on a grid now, but I can put it onto another one if you tell me which one you want". He could only say "you know, the grid". So I sent the drawings to him in state plane. Didn't hear back so I guess it worked for him.

But most agencies don't want state plane for coordinates anymore-they want a latitude and longitude. That includes the SEO and the OGCC.

I doesn't bother me either way, state plane or modified-but actual state plane can be a real pain.

I think there is a certain amount of distaste for the term "modified" state plane coordinates." We often publish coordinates we call "Project-specific" coordinates, and state how one would go about calculating from "proper" state plane coordinates to the project-specific grid. I generally understand whenever anyone uses the term "modified" state plane coordinates, but simply stay away from using that terminology myself.

There's nothing wrong with modifying SPC, provided that the result can't be confused with true SPC. Just subtract off millions and hundred thousands before rescaling them, and document what you did. Most of the grief comes from modifying them by a small scale factor so they look almost like the original.

NJ DEP requires the State Plane Coordinate of the Point of Beginning, the Bearings to be in State Plane Grid, but the distance to be ground, for all Green Acres Projects.

Not the greatest of methods. The last project I did I tried to talk them into either a LDP at ground level or State Plane at Grid. I didn't get anywhere with them.

Subtracting the millions doesn't work because the coordinate is a ratio of the SPC calculated to obtain a surface distance and state plane bearing when the coordinates are inversed. Also they are created to get back to state plane with simple division if a state plane coordinate is ever needed. That is usually only needed to convert between two projects-I can't see any other reason to use a state plane coordinate for a DOT project.

These coordinates aren't going away any time soon, I've never been the least bit bothered by them during the thirty years + that I've been working with them, but I know others really are. I'd much rather work with surface coordinates than state plane in the areas that I work; having a shortage of 0.3' to 0.8' every 1000' from measured distances doesn't make boundary surveying or construction surveying much fun.

> Now I can understand the desire to Rube Goldberg the SPC/UTM systems prior to the advent of reasonably inexpensive PCs in the early 1980s, but I don't understand why this BS survives into the 21st Century.
It's time all the states got busy with Low Distortion Projections.

It's time all the states got busy with Low Distortion Projections.

I don't know about that, some geodesists hate those 😉

Nothing Wrong With That

They understand they are dealing with ground distances. Since only one point of a ground system can be on true SPC corrdinates, the POB is a very good place to start.

Other points may in fact have referenced SPC coordinates which would be different from the ground coordinates of the referenced point. As such it provides a check on scaling and convergence.

A drawing may have several outparcels and/or non separable exceptions which would have their own POBs.

Considering that the point of SPCs is to recover the monument not replace it, it works well.

Paul in PA

For me, SPC is fine for a point addressing system. Each point within a zone has a unique coordinate value that can be perfectly transformed into any other system mathematically. Although, it could be said that UTM and LatLong offer the same performance potential (as an addressing system) with less overhead. UTM is supported by numerous devices that don't support SPC and UTM hasn't been debased the way SPC has been over the past thirty years by users "modifying" the system. Lat Long suffers even less, because it is completely inadequate as a datum for measurement and inversing along the surface it hasn't been abused at all the way SPC has been. (It isn't impossible to measure or inverse along the surface with LL - just not very practical).

LDP fills the niche between an addressing system (take your pick - SPC, LLH, UTM, etc.) and working with surface vectors. It is very capable of incorporating measurements on the ground and providing accurate inverses while still being thumbtacked to the globe, so to speak.

Since making the switch to LDP's, I've not done any multipoint localizations with RTK. I've performed a few single point localizations to translate to existing coordinates, but I've not needed to bastardize the GPS derived vectors to field observed positions. GPS provides identical vectors that the total station does with no dubious on the fly adjustments. Office software (CAD and GNSS post processing) use the same parameters making the effort seamless between platforms.

I can then use software to toggle the LDP to any system I wish that may provide better published constants for point addressing. Is it good for prime time publishing. Eh. Probably not - except for the most technical of clients. But it provides an excellent in-house tool for data manipulation.

(More to come in a future American Surveyor article).