Land Surveyor Forum

Replies

• 

  Billy Brooks August 18, 2016 at 4:03am

  Hi Everyone, One Word comes to mine TRIANGLES,

   triangulation is the process of determining the location of a point by forming triangles to it from known points.

  Specifically in surveying, triangulation per se involves only angle measurements

  Measuring distances to the point directly as in trilateration. The point can then be fixed as the third point of a triangle with one known side and two known angles.

  In geometry, trilateration is the process of determining absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles

  The use of both angles and distance measurements is referred to as triangulateration.

  Or a combination of Triangulation and Trilateration.

  Well that's three words.Triangles are a system of known certainties ,That itself would make a Discussion,Triangles and why we use them,And why they are so important to surveying.And how Triangles can check your work and your equipment at the same time.

  

  Triangle

  A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices A, B, and C is denot…
• 

  CHARLIE B. AYCOCK, III August 16, 2016 at 12:25pm

  Yes, you are absolutely correct. That is the text book, correct method. A few comments come to mind however, keep the required positional tolerance of the job in mind. There is no need to get sub centimeter precision if the requirements of the the job only requires a precision of one meter. I have seen specifications for locating sanitary sewer manholes to second order geodetic precision. Who needs second order geodetic precision for a sewer manhole? Many U.S. ARMY Corps of Engineers dredging projects & beach renourishment projects only require 1 meter accuracy. I love geodetic coordinates. They are the best way to perpetuate legal boundaries. They should still yield to found original monuments. They are most useful when there are no original monuments. Every measurement has an associated error. Replacing an unknown corner using a good geodetic observation is light years ahead of anything else. Experience has taught me that what I usually find where a good location of an original monument should be, is evidence of that original corner!
• Land Surveyor

  Akinboye Ogunola August 16, 2016 at 5:44am

  Already, you have the basic requirement, three intervisible benchmarks. They are all lined up.
  
  The first condition is that you must have their existing coordinate values for the existing points. These are what you will compare with your own measurements.
  
  Next, compute the bearings and the distances of the lines.
  
  Compute the included angle between the middle pillar and the othe two.
  
  Set your equiment on the middle pillar. Do your set up on one of the two lines using the existing coordinates. The equipment will tell you the magnitude of your error when doing the reference setting.
  
  Next, point to the second direction, measure the coordinates.
  
  Deduce the included angle using the existing and your measured coordinates. Compute the accuracy by placing the distance of the line over the difference in your own value and the existing one (the error) using the Pythagoras thing. This will give the linear error. Take your decision, depending on your minimum required accuracy.
  
  Deduce the included angle of your measurement and the existing too. Subtract one fron the othe. The difference should not be more tgan 30 seconds of arc for engineering or Cadastre. This also depends on your Country's Survey Regulations.
• 

  CHARLIE B. AYCOCK, III June 23, 2016 at 10:00pm

  HI Billy, Yes you are right, I have worked for every military establishment in a 3 state radius & also the US coast guard. The key to this question lies in the construction documents.I have also been employed as the project engineer for major construction projects while working for major construction companies If you do good work, it is unlikely that you will ever have a problem. In the unlikely event that you are sued, the attorney filing the suit will try to discredit your credibility as a surveyor. The first thing he is going to do is try to show that you did not follow the construction documents. That is why it is imperative that you report any discrepancies you find to your client or superior immediately. If you tell them "this is what I found & this is what I did or propose to do, it would be very difficult for any attorney to show that you were negligent. In plain language, that puts the ball in their court.
  • 

    Billy Brooks > CHARLIE B. AYCOCK, III June 23, 2016 at 11:47pm

    Hi Charlie, Thank for your support, it means a lot me, the unknowns are how the data on the BM's was first made,What the back site HA was set at.0.00-00 ?, what is the dist to 2, what is the dist to 3, what is the angle from @1 BS 2 FS 3 , the angle error was 0.00-48 sec..IF you BS 3 and FS 2 what is the angle error,next which point is the farthest back site from 1, are all these points on a baseline? if you bs 2 and pt sk 3 how is your angle 0.00-00 they would be in a line to do this. None of this is known????  Also if your site controls are good enough to stake a 25 story building foot print, then building controls are set much tighter and separated from your site controls.

    Layout grid lines on a building is some of the most accurate work you can do,because everyone will use them on this foundation . conc., plumbers ,electric work,elevators, etc. Always make building controls ,you cannot rely on just site controls alone.And keeping them in is enough work.BUT again one set up is not enough and where are the property irons,Do they not exist. I can not give him a thumbs up yet,there is a lot more that needs to be known and done.
• 

  Billy Brooks June 23, 2016 at 2:15am

  First off, i do not think that one setup determines how accurate 3  BM's are to each other.The only data given is from 1 to 3 he does give the data on the back site to 2. Since the ties are that close, will only insure you that the angle between 2 and 3, inst. @1 is good, this does not give you a distance check to 2 it may be good,but the data has not been presented, so how can you say all is good.Triangles have been used for many years to determine how accurate points are. A instrument out of calibration can not produce a mathematical correct triangle.That is your first clue if the instrument is out.I do not think he has this problem,but the main ? is how to check control points,if you cannot form triangles ,then you have to traverse to tie them.Next he asked how to check the bearing and distance,he can only check the bearing and distance of  X's Y's and Z's that he has been given if he hold their coordinates he can not assume his on bearings.You must know how to inverse to do this.This whole thing is how to check ,not how accurate it is and how to adjust it, because one setup does not do it and setting  more points to form triangles insures more control points that you have.And if your work is done with high accuracy  then you may not have to adjust much if any.And  you still have to verify the elev. And I am Done...
• Land Surveyor

  Oluwafemi Muyideen Olaiya June 23, 2016 at 1:35am

  After you have successful applied any of the suitable Least Square methods mentioned above in adjusting your coordinates, then you can compute your distance and bearing from difference in coordinates of points known as Deta (e.g A-B, B-C, C-D) using below formula:
  Distance: square root of Deta Eastings^2 plus Deta Northings^2
  Bearing: tan inverse Deta Northings divided by Deta Eastings
  Note: Bearing result lesser than 180 degree add 180 degree, while greater than 180 degree but not greater than 360 degree, then subtract 180 degree. But greater than 360 degree, subtract 360 degree.
• 

  Chrysostomos Apostolou June 23, 2016 at 1:23am

  If you really wand to check the coordinates of the control points, you must perform a series of measurements and make a statistic analysis.

  The errors are small but you do not know the source of the errors.

  Did you best center the total station?

  Did you best level the total station?

  Did you put the prism parameters?

  Did you put a scale factor?

  Watt the weather condition was at the time you did the measurements?

  Watt is your pole and prism condition?

  There are a lot of parameters giving those errors.

  There is also a theory and method to eliminate them and calculate how accurate you measurements are.

  I am sure if you measure again the errors will not be the same.

   

   

   
• Land Surveyor

  Oluwafemi Muyideen Olaiya June 23, 2016 at 12:31am

  The solution proffered by Timothy Watato is much, much better due to the fact that he has spoken the truth.
  
  In addition, it is highly necessary to check 'controls in situ' before embarking on any form of surveying projects. This will simply give an understanding of errors because controls points are subjected to deformation due to different reasons that won't be mention here.
  
  Solution:
  As a surveyor, who must work according to outlined specifications from your clients or standards required by law for a specific task, this is where Adjustment Computation takes its place.
  Apply any of the suitable Least Square methods below having determined the discrepancies of the 3 control points:
  1) Condition Equation method
  2) Observation Equation method.
• Land Surveyor

  Timothy Watato June 22, 2016 at 6:56pm

  I think the Control is ok, those errors acceptable for Construction. Errors can never be eliminated to zero but can be minimised to suit the accuracy required.

  I think yours is much better for Construction.