EPOCHs CSFs and this Dumb Dirt Surveyor

[paden-cash]

So….are you going to put ALL that on your Basis of Bearing note? 😉

[BajaOR]

It seems like your description of the coordinate system you’re using should mention “Indiana” (ICS?) and “Zone”. Out here we’d say CCS83(2011)(Epoch 2010.00) Zone 1. We have to be very careful not to mix coordinates based on different CCS83 epochs. On the coast, the original Epoch 1991.35 values for a point can be almost 3 feet southerly of the values on the latest epoch. I agree with Mark that you should state how you put your survey on the system by use of a reference to OPUS, to your own “connection to the national CORS network”, or to your connections to ground control.

Mark said “Again, if I go out and record a position in the parking lot, instead of recording the position of the point today, I record the position of where the point would have been on January 1, 2010.” That’s true, but I find it unsettling to think or to tell someone that I’m not recording the position of the point today. I prefer to think of it as “I’m using control whose coordinates relative to NAD83 were determined on 1/1/2010. It’s a “sub-datum”, and since everything is moving, I need make corrections if I want to use my 1/1/2010 CCS83 points(Epoch 2010.00) with another project’s 1/1/2002 CCS83 points (Epoch 2002.00).”

[shawn-billings]

Mark told you well.

I break my metadata into three thoughts: bearing relation, distances and coordinates.

“Bearings related to Grid North for the ______ Coordinate System of 1983, ___ Zone”

“Distances are expressed in [applicable unit] measured {along the grid for the _____ Coordinate System of 1983, ___ Zone}; {horizontally along surface of the Earth}; or in the mountains {horizontally at an elevation ___}. To convert reported distances to Grid (or Ground, or Ground at ___ Ele) multiply (or divide) by the project combined scale factor of _________.

Finally, I would state “Coordinates are expressed in [applicable unit] and are related to the ______ Coordinate System of 1983, ____ Zone, 2011 Adjustment, Epoch 2010.” I used to state that it was HARN or OPUS as it made a slight difference to our database. But I’m not so sure I would even worry about it now, so long as I have the proper adjustment and epoch, nor would I worry about stating what CORS were used by OPUS, but in some places that data is mandated by minimum technical standards, so be aware.

Adjustments and Epochs have little effect on bearings and scale factors, but will have a lasting effect on coordinates as Mark said so well.

[MightyMoe]

Brad Ott, post: 349813, member: 197 wrote: Last week I attended an ALTA/NSPS 2016 standards update presentation by Gary Kent. I returned to the office motivated to start to update my standard drawing template for next year.

Then I came here and saw [USER=10450]@Rich.[/USER] and his brave thread (Plat Opinion) and I was inspired by [USER=6179]@JBrinkworth[/USER] and his posting of a plat for comparison. I decided to steal Johnny’s Basis of Bearing note for my drawing template.

But then I realized that I am just a dumb dirt surveyor, and what the hell do I know about EPOCH’s?

So I sent an e-mail to my friendly neighborhood GPS dealer [USER=1087]@Mark Silver[/USER]. I said,

Happy Friday Mark,

I am polishing up my drawing template and am working on a Basis of Bearings note:

Do you have any advice (1) on the note itself, and (2) how I might readily be able to easily identify the proper info for each survey?

Is there some simple program or such like Corpscon, etc that you recommend?

Do I have to look at the data collector for the EPOCH?

What the ‰ÛÏfront door‰Û is an EPOCH and how in the hell does that info help some future surveyor?

Your friendly neighborhood dumb dirt surveyor, Brad.

And then my pal Mark said, I could make a decent living lecturing about this.

First off, let‰Ûªs be clear that coordinates are accessories to monuments. And coordinates have a relatively low precedence order in the scope of accessories (Distance, Bearing, Natural Calls, Areas, Coordinates‰Û?)

EPOCH: In the United States, all points have some velocity. Areas near the western coast typically have very high velocities, areas like middle of nowhere Oklahoma have relatively small velocities. As you get near the caldera of Yellowstone (like Salt Lake City where I am sitting) the velocities are not negligible.

Because surveyors would like to specify a coordinate and have it remain constant through all times in the future what is done is when you measure a point, you record the coordinate for where the point would have been at some other time. Currently we use Jan 1, 2010 (or 2010.0. For reference, at one second past midnight on December 31st we are at 2015.0 + 364 / 365 = 2015.99726.)

Again, if I go out and record a position in the parking lot, instead of recording the position of the point today, I record the position of where the point would have been on January 1, 2010.

In the future when our kids are surveying, they will be really-really smart and will have really-really good models for translating between EPOCH‰Ûªs (and Frames) and they will think more highly of us for preserving the ‰ÛÏFrame Realization‰Û which is currently ‰ÛÏNAD83 2011‰Û and the EPOCH date ‰ÛÏ2010.0‰Û

You can (and should) have your data collector compute a suitable scale factor. You can go to ‰ÛÏEquip: Localization: GPS (tab)‰Û and check the Grid to Ground checkmark. Then if you are standing in the center of the job, just click on the GPS icon and it will display the correct Grid to Ground scale factor.

If you are OPUS derived, then the position will always be displayed in the current frame (which you can read off). If you are based on a local network, then the network operator can tell you the frame of the network.

If you have already shot a job, you can go to the GG Calculator and compute an average of three or four shots that surround the job, or just use a shot at the center of the job.

In this area it is customary to place GROUND DISTANCES on any plat. To this end, I would suggest that you list ground distances AND grid distances (Carlson will do this for you automatically see: YT link here) Personally I like the Ground on top and the Grid on the bottom in (parentheses). We see a couple of feet per mile between G&G. You however are going to see 0.28‰Ûª per mile which might not be a big deal most of the time (the distances for 100‰Ûª courses are going to be the same, right?)

I would specify the EPOCH as ‰ÛÏ2010.0‰Û not ‰ÛÏ2010.0000‰Û, but that is nit picking.

I would also write something like: Elevations are GPS derived: A NGS OPUS-STATIC occupation was performed on CP1001. The ellipsoid elevation of CP1001 was reported 631.012 ft and the orthometric elevation was calculated 731.214 feet using GEOID 12B. All other elevations are orthometric heights derived from the ellipsoid height at CP1 using GEOID12B.

Merry Christmas!

Mark

And so I said, I am tempted to post your email text to beer leg to spur some more conversation.

To which my friend Mark said, There will be lots of comments. Hope I don’t get beat up like I did on that shaking video.

I like it ok

but a couple of things,,,,
without coordinates there really isn’t any reason to state an Epoch or even the realization

bearings in NAD83 (86) won’t be any different between two points than bearings in NAD83(2011).

There is a statute (why anyone did it is another issue) that defines the verbiage for state plane in the states I work in,,,,,I use that

It’s actually Stat 34-25-101 (through 102) for Wyoming and it says the it’s to be called the “Wyoming Coordinate System NAD 1983, East Zone”

I assume there is one for your state,,,,,

Stating that distances are grid is all you really need to do, you can give a combined factor, but each point and each line have a unique one, if you are showing both, then I would state my factor, or if you are only showing ground, I would also show it.

[JBrinkworth]

Aww, shucks.

I suppose I could have fleshed out the SPC IN EAST… part a bit. I also should have included the convergence angle.

In general, the biggest reason I chose to include 1) the coordinate chart and 2) the details of the coordinate system was to perpetuate the location of the monuments shown on the plat at the time I surveyed it.

My grandpa surveyed this section in 1973 and broke it down accordingly. If you examined the plat, you noticed there was an 11.6′ discrepancy at the CN 1/16. I found it to be 11.6′ North of where the plat said it was…at midpoint. After thoroughly examining the field notes/file, ground evidence, testimony etc. I could not come to a conclusion that this corner had been moved, as discussed in the Surveyor Report of the plat. I wanted more than anything to verify that it had been tampered with. I started in the field crew at 15. I have come to learn that monuments that he and my great uncle, Dave Brinkworth set are where they said they set them. He was good and the crew was good. BUT, the only evidence that I had to refute this monument’s location was the math. It just wasn’t enough.

Long story short, if I would have had a coordinate chart with the approximate location of the major corners and reproducible coordinate system info, I could have lessened the amount of uncertainty of this corner. Hopefully, I have provided enough information to assist a future, retracing surveyor to reconstruct the coordinate system I was on. At least enough info to be able to identify an error on the magnitude of 11′.