Completely Out of Control

There's a lot to unpack here. Any tight control, in other words control that has good geometric internal consistency, can be merged from terrestrial to GPS using an LDP. Or it can be rotated, translated against State Plane. That's horizontally.

Vertically a calibration might work, however, we're discussing Hawaii and I'm guessing the Geoid contours are about as extreme as anywhere. What that means is there won't be a plane tilt that will match no matter how it's done if the figure is too large. How large is too large? I have a small airport that no amount of calibration would "fit" level runs. So 1-1/2 miles N-S, by 1-1/4 miles E-W defeated any attempt at calibration. On the islands that size limit will probably shrink considerably.

It's best to apply a Geoid model, I don't know about Hawaii but for that small airport we now can use GPS with Geoid18 and hit control vertically less than a cm consistently and that's RTK. Using calibration for the same site there would be more than 5cm in places.

I would first collect everything in State Plane. Then inverse points and chart how the angles and distances compare to my terrestrial survey. In Access there is an option button when you inverse to see ground distances or grid distances. Your terrestrial distances should match closely to ground when you inverse. Once you calibrate you lose that clean comparison.

If all that data looks good you have a choice, design a local LDP that matches your terrestrial survey, scale up and probably rotate SPC, or calibrate.

Without TBC and only Access on a controller this will be difficult to accomplish.

Calibration isn't my preference ever. I quit doing it almost thirty years ago and haven't regretted that decision. Without TBC I'm not sure a stand alone LDP can be designed for your site using the controller.

Dunno where the idea came from that TBC or StarNET is necessary for developing an LDP.

Check out appendix E of this document:

https://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.1.pdf

The equations for computing grid scale factors are a bit tedious but easily automated. Especially if you're working with just TM or LCC projections, not Oblique Mercator...

In any case, there are ways to develop LDPs without purchasing specific software packages.

I'm with Mighty Moe on this one. However, i have no idea how you would even begin to do a lot of what you want without TBC. It's pretty much a requirement when using Trimble GPS. Otherwise you're going to be fighting data.

I would tie the data on state plane, probably just an opus based solution. Move all your existing control coords to state plane, set your scale factor in TBC and you're done as far as setting up your system. How your existing control 'fits' the GPS is another thing entirely.

I'll second that on computations. It's mostly 8th grade stuff.<div>

Work in SPC.

Multiply the scale reduction by average 1/csf and you have the ldp scale.

Use sin of lat X delta long = covergence as a basis for the new central meridian by applying your rotation to the convergence and working backwards.

Apply the north and east shift from your base coordinate to desired coordiante to the false northing and easting.

Test, test, test...done!

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Rover, I don't think it's a question of only being able to do it with TBC. From what the OP stated is all he has is Access and a DC, even if the projection parameters are developed by any formula or program, how then is it imputed to Access using only his DC.

I can't answer that cause I tried unsuccessfully once, got frustrated in the field, and simply collected data and fixed it later.

If anyone knows how that can be done, I hope they chime in.

Rover, I don’t think it’s a question of only being able to do it with TBC. From what the OP stated is all he has is Access and a DC, even if the projection parameters are developed by any formula or program, how then is it imputed to Access using only his DC.

The ability has been there for a long time - certainly long enough that v2017 can do it.

Create job, go to properties, then coordinate system, select "Key in parameters", then "Projection", and enter in the type and parameters.

Then on to Datum transformation, which will almost always be a "three parameter" null transformation.

Ignore the Horizontal adjustment and Vertical adjustment sections, since this is not a site calibration.

Tap Accept and voila! The job is now in a custom projection.

Rover, I'm doing a terrible job of explaining what I mean. In Access it's possible to set up a job with a custom projection. What I think the OP wants is to set up a projection that incorporates his control point values (XYZ). That I can do in TBC, however, in Access the options are more limited (at least from my experience, I have always controlled projections from the office software).

The easy way would be to locate the points with GPS, place your origin point on a control point, holding the GPS L, L, H and the record XYZ of the control point.

Use a scale factor that places the LDP at surface. Inverse the points and apply a rotation angle to then mimic the GPS projection to the XYZ values. If that's an option in Access I missed it in the field, but in TBC it's quite available.

The more difficult way is what Doctor Herb discussed in a seminar which is to place the origin point so the Lat, Long, XYZ values pass through the points.

Frankly, it's best to set up a good regional LDP, locate project control points and rotate the old data to the new values. Sometimes, that isn't possible if the control is for a finished design and needs to be held, but everything I work on these days is GPS based anyway.

Thanks to all for your time in this discussion. Very helpful in wiping a couple more cobwebs from those lonely parts of my brain. Mahalo.

I think in general I’d like to either spend the time figuring out my own LDP

You will never regret the effort it takes to do that. You are headed down the right path. When you begin a control network using total station observations you pick a point pair as a basis of bearing. I like to use that same basis for rotation when designing an LDP to fit an existing coordinate system. Also like to use the first setup point in the network as the origin point of the LDP. Designing an LDP gives you so much more control over what is held in calculating the parameters than a calibration. If I've said it once I've said it a thousand times. Friends don't let friends field calibrate. Field calibration assumes the measurements made to the held control points are either perfect or equally imperfect. That is never true.

Dave, there is a lot of moving parts in your question, and personally, I think you're overthinking this. I'll try to summarize.

My thinking is that you will find MUCH more utility if you put your survey on the grid and stay on the grid. The connection to the grid via CORS or OPUS is too easy and allows you to move wherever you want and have a repeatable experience.

First, you want Ground coordinates. Not really, what you want is a ground distance. If you want to run on the ground, then don't really mess with an SPC. When you make a "here position" and then you "calibrate" it to "a value", you essentially are making a mapping projection, complete with scale factors and angles of convergence. The further you move from your base point, the more it gets off. If you had a statistics class in college, think of the words "relevant range". Now you can calibrate to points "around" your site through a host of procedures (horizontally or vertically but I'll get to the Z component) and it gets even worse then since you have now a polygon of control and when you step outside that theoretical polygon, scale rears it's ugly head, and the worse your control was, the faster you fall off.

Vertically, you want one of two methods to constrain to. The first is ONE SINGLE POINT. This keeps your plane level (for the most part) and is a vertical transformation. The next is SEVEN OR MORE points surrounding your parcel. Anything less and you "tilt the plane" and the verticals get nasty quick.

Consider this as an alternative, and I think you'll find MUCH better bliss through it. Make a "here position" in an SPC environment. Post Process that point to OPUS. Yes, yes yes. I hear you. You want ground distances. Just hang on. Keep it on the grid. Then when you do a tract a mile away, DO THE SAME THING. Now, the two data bases literally tie together and you're WELL on your way to making a solid data base.

What's that? Oh yeah. Ground distances. Okay, draw the whole thing up in AutoCAD, like everything. Wait till the VERY last thing, and scale all of your linework up by the reciprocal of the combined scale factor. Annotate your lines. You'll have grid coordinates that aren't fussy, and surface distances. Also, at some point, you'll hate that you chose this and eventually come around to keep it on the grid.

I've typed up the culmination of the past 25 years of surveying with GPS and how best to relay it to the clients and for longevity. I've only EVER worked on one project that the deliverable was so large, for the scale factor to have made a change in the acreage. I reported both.

There is nothing wrong with the LDP or the crowd that promulgate them. If you find you "move around" a lot, I don't think you'll like it and having to play in the right sand box. They're not hard to make but at the end of the day, it's one more thing to keep up with. If your scale factor is greater than 0.9999, then it doesn't matter on a 40 acre survey (mostly). I would save you the nearly decade long "beat my head against the wall" session to come around to this thinking that all kinds of things. I had some great teachers (they didn't know they were though) regarding the methodology of this. Not to step on any one's toes, but Shawn Billings is one of the best at this and if you want to chase this rabbit, call him. He's one of the nicest and smartest guys I know of the subject. He and I do it differently, but we've followed each enough that we read the field notes and make each others data sets relative to each others before we ever leave for the field.

Good luck.

To start a JOB file for site calibration, choose “ no project, no datum” since the site calibration will create that projection.

Just like a resection, you may find NOT using every control point observed giving you lower residuals since pieced together total station data over five years will have points that don’t match into other points as well as others do.

The purpose of the calibration is to use GNSS on a local coordinate system. I rarely use a calibration, but I would think if you switch the coordinate system setting back to SF 1, you would not be able to export GNSS observed points. And TA has had improved scalding function for export, but I’m not sure if 2017 has correct scaling working on export. You could fairly easily scale values in excel.