Hey all,
This is sort of a newbie question, but I'm hoping you all might have some guidance...
This summer I've been tasked with setting up a total station (we'll be using an older Topcon GTS-230) for some mapping work. I've taken points using the prism, etc. but this was all after the TS was setup.
Specifically, I need some advice or pointers on how to setup a total station grid. I've been able to find a whole bunch of information on leveling the total station, so I think I'll be OK there. However, most of the videos and manuals I've found online seem to skip the next step: setting up a grid.
We have a known point that I'll be setting up the TS over. I'd like to shoot in UTM coords, so the grid "0" point will be the UTM coords of the known point (yes?).
My question is, what is the next step? How do you tell the TS which way is North (and is that magnetic, grid north, etc.?)? I've read about backsight setup, but I don't think we have another known point in the area. Without this backsight, do all the points we've taken for that field day need to be altered through post-processing somehow?
Also, as a corollary, we also have a Topcon FC-120 field collector unit. Are there any neat ways to use this in the field? Or in combination with the TS? Or will it just collect dust if we're only shooting in points w/ the TS?
Thanks for the assistance!
I guess I don't know what you mean by a UTM Grid. If you are going to reduce your coordinates to utm that sounds pretty convoluted.
I would say that you definitely need to establish a backsight and establish a bearing on that line. I'm not sure if I just don't understand what you need, or if you might be in a little deep over your head. Maybe some of the other guys can help you out more than I can.
Can you just set up a local grid of every 100' or some defined distance? Does your project scope require some kind of reduction to UTM coordinates?
I think that you're going to have to define what you mean by "setting up a total station grid." you're opening up a huge subject, regarding whether you want to be on State Plane Coordinates, a local project grid, or what ever.
The Total station knows nothing beyond what you tell it. For a local grid just assume a backsight point and bearing. For a State Plan Coordinate system you'll need to tie into the State Plane Coordinate system, and that requires either a bunch more work or more specialized equipment such as gps, or you can do a sun shot (or other astro observations), but don't do that with your total station!
What's your goal with this new fangled equipment? Apparently you're not working under the supervision of a land surveyor, so what's up?
> I guess I don't know what you mean by a UTM Grid. If you are going to reduce your coordinates to utm that sounds pretty convoluted.
>
> I would say that you definitely need to establish a backsight and establish a bearing on that line. I'm not sure if I just don't understand what you need, or if you might be in a little deep over your head. Maybe some of the other guys can help you out more than I can.
>
> Can you just set up a local grid of every 100' or some defined distance? Does your project scope require some kind of reduction to UTM coordinates?
You're right, that wasn't too clear. I meant to say that, instead of an arbitrary grid (e.g. X= 1000, Y = 1000) I'd like to setup the TS on the known UTM point (e.g. X = 3881511 Y = 650011). This way I don't have to convert points that I shoot in later to UTM.
It doesn't really matter, just wanted to avoid having to do too much to the data afterwards.
I guess I was really looking for advice re: setting up the backsight.
thanks!
> I think that you're going to have to define what you mean by "setting up a total station grid." you're opening up a huge subject, regarding whether you want to be on State Plane Coordinates, a local project grid, or what ever.
>
> The Total station knows nothing beyond what you tell it. For a local grid just assume a backsight point and bearing. For a State Plan Coordinate system you'll need to tie into the State Plane Coordinate system, and that requires either a bunch more work or more specialized equipment such as gps, or you can do a sun shot (or other astro observations), but don't do that with your total station!
>
> What's your goal with this new fangled equipment? Apparently you're not working under the supervision of a land surveyor, so what's up?
Thanks for your input. So if I were to just setup a local grid (forget all the talk about UTMs), how do I setup a backsight point and bearing?
Sorry for the silly questions, I know this is probably survey 101 stuff.
Total stations collect data using a polar grid system, direction and distance. You need two points to start, they can be known or assumed, one of those points is used as a Backsight, IE reference point the other point being occupied by the TS, all angles are turned using a known BS as zero or whatever you chose, I like 20 seconds on the back sight because of note reduction. Then you turn the angles and shoot the distance including your next set up, when done at that point, move up and occupy the next previously tied setup point, also move the backsight ahead to where you had just been. Called traversing and it ties all of the data together so you can compute rectangular coordinates to work with. Sounds like you may need some training, go get it. Lots of things to take into consideration in order to obtain reliable data. What I stated above should not even be considered a primer on traversing combined with sideshots to surface features.
jud
You can assume any arbitrary direction, like a best guess at North, and build a local coordinate system from there. It won't tie into anything else in the world.
If you want you local work to align with the world, you need some way to determine direction better than a rough guess. The principal ways of doing this are another known point in the same coordinate system (if you are so lucky), compass reading (if you can stand the low precision), survey-grade GPS vector between any two points a reasonable distance apart, and astronomical measurements.
Myself, I'd look up how to do a Polaris (North star) sight. This would need to be rotated by the UTM convergence angle for your location to match the grid north of UTM. Solar measurements can also be used, but you'll do damage if you point your type of instrument at the sun without the proper filter. If a Polaris sight is too difficult at your level of knowledge, then fall back to the best compass reading you can get and correct for declination. You might be within a degree, which allows a twist of about 100 ft either way at a mile on your local grid relative to what GPS or careful astronomic work would give.
Also be aware that if you use UTM or State Plane Coordinates, those are on a grid at the ellipsoid model of the earth, not far from sea level. So surface measurements with your instruments would need to be corrected for elevation and grid scale factor to match those grid systems.
If you want a relatively precise bearing, I would say that you could either do that with solar observations, star observations at night, or GPS equipment. If you want a rough bearing, maybe you could assume a bearing with a compass. Establishing a precise bearing would take a little higher level of training or studying, and probably not be well explained in a paragraph on a message board.
The way normal surveyors do this is to set the TS on a dummy coord. 50000/50000 is an example. Then, using a hand compass, establish a backsite on something.... tack in tree, with reflector tape would be an example. Then, shoot all the stuff you need, change setups etc. Then, turn an angle to the sun, with precise time, for a sunshot, or to POLARIS for true north. Then, using tables or computers, rotate the whole job to GRID north, as in STATE PLANE brgs. OR UTM, or whatever SYSTEM you need to be oriented to. This also can mean scaling the coords.
Rotate and Translate are your friend! 😉
N
> Sorry for the silly questions, I know this is probably survey 101 stuff.
Retired about a year ago from nearly two decades of teaching survey basics. The background you need to get started would require about 8 - 12 hours of one on one with you and equal study time on your part. As others have said you need training to get started. Give us an idea where you are located and what type of surveying project you are contemplating. We may be able to direct you to someone that can help get you started.
I would also caution you that if you are anywhere in the United States and thinking about contracting for survey work you need to be aware of state licensing laws. Training requirements and what is regulated varies in each state. The Land Surveyor Reference Page, Land Surveying Rules & Regulations Page would be a good place to start researching state laws and regulations.
Then, turn an angle to the sun, with precise time, for a sunshot,
Just be real careful with that one, you could wind up blind, or burn out your TS, stick with the other suggestions until you have a better idea of what you are doing!
Ken is right
You will need a solar filter, to shoot the sun.
UNLESS you have an old inst with NO EDM, and then you shine the sun BACKWARD through the scope, onto a pc of paper, and watch the cross hair pass the edge of the sun. These methods are BEST done with a bit of HANDS on instructions.
Another method is a pair of L1 GPS units, posts processed, Static.
N