Very Basic Total Station question.

This is the simplified response...You either key in your back sight azimuth in your data collector, or have coordinates for both points in your data collector. In the case of not having a back sight, you would record all of your angles and distances from an assumed coordinate (occupation point) with an assumed heading (back sight), and figure all of the geometry in the office.

Posted by: @timd1971

How does the total station know where NORTH is?

The short answer is...it doesn't. All measurements are based off of whatever horizontal angle the instrument is reading. If someone orients that instrument to something in the real world, then that is the connection to the real world.

Someone might orient the instrument so that zero is at the backsight. Others might orient the instrument so that the angle reading at the backsight matches the grid azimuth in whatever system they are working in, or maybe a geodetic azimuth. We could also use the stars or the sun to determine astronomic north and set our zero there.

It's possible to not bother with any of those methods and still get good data.

When I was learning this stuff, it was helpful for me to think of each total station setup as a separate dataset in a different coordinate system. Because we (usually) observe common points in all of our setups, all those setups can be pieced together based upon those common points.

Then that entire block of setups - the whole survey - can be oriented based upon something else, whether that is a set of monuments, a star shot (astronomic north), whatever.

Or we can just pick a random bearing and hold that, and not even worry about it. It might not even matter where "true" north actually is. Generally speaking as long as the survey is consistent within itself, it is (are?) good data.

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It's an oversimplification, but might help.

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Unless you're exhausted like I was the day I arbitrarily set an Azimuth to my backsight unknowingly on a job that was already transformed from grid to ground running along very close to actual due west...7min37sec off to be sure, and still gives me nightmares of the slight but significant assumption of coordinates I had to fix .

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Jeebus. I'm going to have to have a beer. And a bourbon now.?ÿ Shudder.

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Personally I like to give the total station a good spin and wherever it stops, I call that (assumed) NORTH. I can always use my compass to get a rough magnetic or true north bearing to rotate to later, or set up a couple GPS receivers on the two points and let them give me a GPS bearing to rotate to, or shoot in a couple of monuments with a record bearing between them and use those. I could set up on on of those points and do a Polaris observation to get (astronomic north) or use the sun in conjunction with an ephemeris. Frankly my good man, the total station doesn't give a damn where north is, it just measures angles and distances relative to the line I defined by two points to allow me to compute coordinates and traverse and measure to whatever, relative to those two points. How I go about orienting is just a matter of rotating those coordinates to whatever best fits the bill or best allows me to orient to someone else's past work to try and get my work in sync with theirs. North comes in many flavors, but they all represent a simple point of reference.?ÿ

Thanks!

I am used to GNSS systems, so it was just easy, LLH and state plane or UTM coordinate system.

Haven't really entered the total station realm yet, but curious when clear sky view not available or for vertical layout.

So it seems however I arbitrarily set up the total station and its backsight for reference, the points shot will need to be transformed back at the office later anyways...?ÿ or transformed in the data collector software during point observations.

I heard of a party chief who drew his north arrows to point to his favorite bar, wherever he was.

Posted by: @williwaw

Frankly my good man, the total station doesn't give a damn where north is, it just measures angles and distances relative to the line I defined by two points to allow me to compute coordinates and traverse and measure to whatever, relative to those two points.

That was my initial thought, but wasn't sure...?ÿ thanks all for the help!

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It knows where (grid) north is based on the coordinates of the points you're occupying and backsighting.?ÿ Unless you're working with assumed coordinates then you need some other way of determining which way north is.

Posted by: @timd1971

I am used to GNSS systems, so it was just easy

This is technically true from a pure operational standpoint. GNSS is always easy when you don't have to relate it to the real world. Projections like state plane and UTM are just pure math, and coordinates are directly computed from geodetic values, so within themselves they're always going to be consistent. But they're still only approximations of the real world.

When you do have to relate GNSS and projections to the real world, it might be easy, depending on where your project is located. Or it can get complicated really fast.

Once you introduce total station measurements into the mix, you're working in the real world by default, and blending GNSS with conventional data takes it to a whole another level. That can be "easy" too, but it takes a training, education and experience to get to that point.

Good on you for asking questions. I know a lot of folks who never did, assumed they knew it all, and got burned.

A total station is a protractor that can measure angles and distances.

You should have a ton of research and paperwork done before you do anything but I'll say for a backyard guy with a total station, it makes it a lot easier to find 2 pins on line and go off your research from there???North is just a myth????