Hello, firstly and most importantly let me ?ÿpoint out I??m not a land surveyor (I wish), I have no training, I just have an interest in the science of surveying from a purely geeky, novice self taught learner level, so please forgive all the errors and what will seem like extremely basic or even pointless questions. I really don??t belong here but I thought where better to go for answers than to a forum of professionals.
My first question for you all??
After?ÿlearning about some of the basics of using a total station is based on how it seems to my untrained mind that all the different things you can do with the systems that I have come across so far all seem require known point(s) to start.
Then how do you find the X, Y and even Z of an unknown point if you are somewhere with no known points around? Essentially as surveyors how do you start with a blank slate and find that first known point??ÿ
Thank you in advance for your answers.?ÿ
This could become a very interesting thread.....
Before GPS/GNSS were standard tools of the profession, we would either start at NGS monuments with published coordinates or we would assume X,Y, & Z coordinates on our initial traverse point and a compass heading to our initial back sight. Now we use the GPS/GNSS tools to locate our control points, and most often than not, process that GPS/GNSS data using OPUS, the USGS processing system.
Most land surveying jobs do not have a point with known coordinates to start from. Rather there is a description or plat to identify one or more points, and hope that previous work has left a monument to find there or nearby as a starting point.
Finding coordinates in a world system may be optional and was rarely done before GPS became common.
In many central and western US states, rural land parcels are described by the Public Land Survey System (PLSS), which you may want to read about. That is a sort of coordinate system, but has enough irregularities that you can't predict GPS coordinates better than yards at best without a nearby known point.
or we would assume X,Y, & Z coordinates on our initial traverse point
Assuming you know coordinate geometry, the above method should be sufficient for assigning values to the remaining items called for to complete a polygon. This may involve angle to bearing conversion or vice versa. ?????ÿ
When working with plane geometry, that is treating the world as though it were flat for purposes of a survey covering only a limited area where convergence can be practically disregarded, the point of origin can be be arbitrary because everything is relative unto itself. In this case the unknown coordinate at the starting point can be whatever you want it to be. The process is rather simple in that the angles and distances, also known as polar coordinates, can be converted using basic trigonometry, into latitudes and departures, northings and eastings or x & y coordinates, to make plotting easier. Essentially what's going on is a back and forth between these polar coordinates and cartesian coordinates. Unless referenced to a projection to reduce distortions given the curved surface of the earth, (imagine trying to place a sheet of paper over a basketball and wrap it around without creating creases), the simplest approach for small surveys is to use an arbitrary plane system, or in other words to treat the world as flat, in which case it makes no difference if the corner of the sheet of paper is 5000,5000 or 500,000,500,000, because it's only relative unto itself and not the larger real world and makes no attempt to account for distortions.
Just because I'm paranoid, doesn't mean they aren't out to get me.
Others have done a good job answering your question. ?ÿ
Evidence called for by the original survey is what controls. ?ÿMeasurements and the coordinates derived from them are subject to error. ?ÿThere is no error in an original monument that is undisturbed.
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Looks like they have gotcha covered very well. ?ÿJust a thought when you look at the plane coordinates northing and easting etc. make sure you dont use the same quadrant order as we did in math class or physics. ?ÿSame math just different quadrant order the old roman numeral order. Thats a slight difference. ?ÿAlso they mentioned assumed coordinates and off of NGS published monuments. Also you can use solar or polaris or othe astronomical observations to get a latitude and longitude (not to be confused with latitude and departures) but the geographic coordinates to get a position and direction to another point azimuth. Or magnetic like was mentioned above. You can even assume one as stated the boundary monuments are relative to each other. And later rotate to a platted previous bearing if need be.?ÿ
another approach that I am surprised that the old timers here did not mention is using a baseline approach. Very easily done on some jobs not much different than latitude and departures same math if using angles. ?ÿSine and cosine laws. Up and over. One does not necessarily need coordinates to perform a survey it just makes it much easier to plot and do math. Read up on plane table surveying. Many ways to solve math problems. But coordinates are very easy and have a history. ?ÿ Glad to see you are interested in this. Join up and try your hand at a great profession. ?ÿ?ÿ
It's a head scratcher for sure. Usually I shoot something and then something else, and inverse a line between them. That's North unless it's East. The British Empire was mapped using a combination of intersected points never occupied together with resected (occupied) points never intersected.
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With a transit you can rule the world. With a total station that measures distances, you have no excuse.
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Think of it (any given survey) like a car. Put it together right, and it'll work. Drive it from a, to b. That's translate. Turn it. That's like rotate. As long as the whole car moves together, as a unit, things don't come apart.
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Finding the first monument, then another so you have orientation then it??s easy after that.
if finding the first monument is too easy then after that the survey is cursed and will be nothing but trouble trying to find the rest of the monuments. So try to pick a more difficult to find monument to start.
After learning about some of the basics of using a total station is based on how it seems to my untrained mind that all the different things you can do with the systems that I have come across so far all seem require known point(s) to start. Then how do you find the X, Y and even Z of an unknown point if you are somewhere with no known points around?
The short answer is you need to start on a known point and then use the instrument to measure your way towards the unknown point.?ÿ And yes, depending on how far away the known point is from the unknown point it could be a labor intensive process.
Essentially as surveyors how do you start with a blank slate and find that first known point??ÿ
You seem to be mixing a couple different ideas here that aren't quite the same, so I'll try give an explanation of how I understand it.
As surveyors we measure between physical features, for example, 4 fence posts each of which marks the corner of a 100 acre square piece of land.?ÿ Say I measured between the fence posts with the total station and I was able to confirm the sides are each 2087.10 feet long and each post was due north-south or east-west of the next closest post.?ÿ I have dimensions for this piece of land now, but the only way I have of describing exactly where it is located on the planet is by saying hey, it's between these 4 fence posts.?ÿ Does that make some sense?
The other idea you mention is the x, y, z which is a Cartesian coordinate.?ÿ Coordinates are just a pair of numbers on a grid, you can't see or touch them, they're abstract. You can certainly assign a coordinate to a physical feature, like one of the fence posts above, but it's not necessary in order to determine the size of the thing you're measuring.
For the sake of my example though let's say I created a large Cartesian grid and I said OK the northeast fence post lands on my grid at the point y = 1000000 x = 1000000 (I'm going to ignore the z value for now because surveyors work in horizontal distance not slope distance).
Technically, I now have 2 ways of describing where this 100 acre parcel is located on the planet.?ÿ It's between the 4 fence posts and also on "BStrand's Grid" the northeast corner of which is located at coordinate 1000000, 1000000.?ÿ Hopefully this makes some sense?
So getting back to your questions:
Say the unknown point that I'm looking for is the center of my square piece of land.?ÿ I know it lands between the fence posts so one way I can get to it is to look around for the fence posts, measure halfway between a pair, and then halfway across or I can go to coordinate 1000000, 1000000 and then measure south 1043.55 and then west 1043.55 (or vice versa).?ÿ The problem with the coordinate is it's abstract so you can't walk up to it and start measuring.?ÿ The only way you have of knowing where the coordinate is on the planet is by finding the fence post that it is assigned to.
So, essentially you always have to start at a known physical feature and then start measuring.?ÿ Coordinates are great in that they let you use math to quickly compute various things like angle and distance between points, area, perimeter, etc but ultimately since they are abstract they won't be able to help you on their own.
And remember this only applies to a total station since that's what you mentioned in your post.