Do all grids not align to true north?

@rover83

I do not get paid for this. I am building my own home on my own land. I did all the AutoCAD design work and I am physically building the home myself (with the exception of the dirt work and concrete work). I rented the R12, the controller and accessories from a major surveying company, to whom I explained my two goals of staking a crosshair of North-South and East-West to align the house, driveway and others to, as well as getting the lat long coordinates of 20 randomly placed GCP target flags for later import into aerial drone photography (to correct those images to true locations). The survey company programmed, calibrated and demonstrated the R12, controller and accessories to me for my specific location and goals. All that worked as intended. But they failed to mention that the tool was set up on state grid and not lat long (which I mentioned was the goal). But the coordinates were taken with high precision and from what I understand, they can still be converted into lat long, using the NCAT tool, so that at least the second goal (the lat long GCP points for the drone image correction) can still be used.

Thanks,

Marco

There's many parameters involved in GNSS (GPS for the Layman) that a lot of registered professional Land Surveyors don't understand so you're not alone in your inquiry.

Do you know if you were staking Grid or Ground points?

Were the points you took stored along with the metadata files which the data collector recorded & stored in addition to simple Lat & Long?

Unless you're trying match "north" alignments to exact tolerances like Stonehenge or Chichen Itza, where you can observe solar alignments at the equinoxes, a simple compass reading would probably suffice.

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You should be able to calculate offsets of a few feet from your crosshair points to get geodetically aligned points.

How is it that grid north and true north being different came as surprise? Itƒ??s quite basic.

However, there is an antenna array at Brownfield airport built for tracking satellites and defense. US Navy installation. The array was called out to be aligned to astronomic north. Initial staking had to be signed off by an independent PLS based on 2nd order Polaris observations. And surprise! It was BUILT to grid north. My company did an as-built to confirm its geodetic and astronomic azimuth by numerous lengthy Polaris observations. And explicitly not based on GPS. (GPS+Laplace agreed with T3 Polaris to subsecond.) this was around 1989, so GPS software and procedures, (5 channel L1 only, 4-5 hr availability)was not fleshed out yet.?ÿ

as for the East west line, it may surprise you that constant latitudes are arcs.?ÿ

https://spp.fas.org/military/program/track/spasur_at.htm

@xuv224?ÿ

The short answer to your question about coordinate conversions, achieving one of your goals, is YES. There is an assumed ellipsoid underlying lat/lon measurements and state plane coordinates are derived from that ellipsoid. The conversion from lat/lon to state plane is the?ÿforward conversion and from state plane to lat/lon is the?ÿinverse conversion. Both are pure mathematics accomplished by rigorously derived formulas.

However, whatever coordinates you input are going to be the ones that are converted. How close those coordinate values match your ground monumentation is a function of your skill in having the instrument precisely placed and properly used. If you take a GNSS reading on the exact same point on two different days, chances are good that the measurements will differ. If you did everything right, though, chances are that those differences will be minor.

Establishing true North-South and East-West lines is theoretically easier now than it was when PLSS lines were first being established, but it's still difficult and there will be some error to be accounted for in any such line. As @Bill93 pointed out, you are very close now, so don't be discouraged. I used to refer to a particular learning process to my students as LBSU, which stands for Learn By Screwing Up, and I think that at least half of what I know was learned that way.

You seem to be going to a lot of trouble to get a true orientation for your house. Are solar panels involved? If so, there are several variables involved there that may make as much difference in performance as a degree or so off in facing "true" South.

These guys here, except for me, are true professionals, and we all like to share knowledge. In return we usually all learn something about applications, levels of performance, or just general knowledge. But the profession is not easily learned nor easily practiced, so folks sometimes get a little testy. You can always trust their judgement and advice, though.

Thanks for sharing your problem, hang in there, and best of luck.

?ÿ

you have all the tools to adjust the data. you have lats and longs on your points. take the ngs tool enter the lat for your north set point using the R12 enter the long at the center hinge point allow the NGS tool to calculate the State Plane Grid XY for the correct north point. Compare eastings and move accordingly. Repeat for the other points. Simple, easy peasy. Anyone here can do it in a few minutes.?ÿ

You need to do it to understand what you did.?ÿ

Andy said the rotation is 1d16'.?ÿ

In my head I know that would be a shift of +or-2.2' in 100' you shift each point that if they are 100' from the hinge point and be close, prorate using that number against the actual distance if they aren't 100'.?ÿ

As far as setting up your house True north you will not want to use the east-west points. Get the north-south line and let the contractor square it up from there. If the building can't be constructed square then you have bigger problems.?ÿ?ÿ

Posted by: @xuv224

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I used a Trimble R12 Rover over an RTK network on land in North Texas a few days ago. The goal was to stake out a line pointing to true north (and another line going due east-west).

The collected data was in the state grid ƒ??Texas North Central 4202ƒ?, formatted in Easting and Northing, in US survey feet.

The points were staked out along the north-south line, starting with a reference point, then further points on the 180 degree line south of there.

When these points (Eastings and Northings) are then converted into Lat Long on a site like https://www.earthpoint.us/StatePlane.aspx they come up with a different longitude for all given points, even if the exact same Easting is used to input into the converter.

If the Easting number of each point stays exactly the same and only the Northing is changed in the above conversion website, should the resulting longitude not also stay exactly the same?

Thanks,

Marco

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Read up on geodetic surveying. Plane Surveying is simple. Geodetic surveying ƒ?? not so much

@xuv224 in a Trimble controller choose ƒ??no projection no datumƒ? when starting the job.

sarc on - For crying out loud, the ancient Egyptians did it using a crude plumb bob, sticks and the sun, and were only off by something like 2 minutes, if I remember correctly! - sarc off