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Mar 04 2012

Traversing vs. resection

  After careful research I realized my understanding of resectioning was not clear. Resectioning a control point is not the most efficient way to establish new control in alot of ways its a waste of time. A better way of survey control setting would be traversing.

With resection I noticed that you can use 3 known points to determine a unknown point.The problem with this is, I would need to be set up some where roughly in the middle of the three points because according to the owners manuel for the total station, the further I am from the center of the points the less accuracy I will have in creating my new control points. I observed this to be true because no matter how many new points I created they were all off by and angle of at least 1'.

This led me to consider another method of creating control; traversing(picture shown below). Traversing is the method that all modern surveying is done with. This method allows me to broaden my survey network while also creating new control points. Triangualation deals with an X,Y cooridinate system and the pythagorean theorum in order to determine the exact differences between many points. Traversing uses a R,Theta coordinate system of vectors to determine the relative distances between many points. Where you would use a magnitude R and a direction determined by some angle "Theta". What you see below is a "closed traverse". This is the most widely used surveying method today because it is quick and efficient. basically what you do is you begin and end on the same point calling them different points. You have at least three traverse in a loop. What you do is collect many measurements of the distances and angles inbetween three points. By setting up on one point and backsighting and forsighting two other points. After this it will propogate the error and evenly distrubute it throughout the three points. This process is repeated howevermany times until you have a sufficient amount of control points to cover all your mapping and stake-out needs. When your loop reaches the first point agian, you would simply give that point the next highest number and throw a control point there. Then after this you would do a closure check which has two components. First I would check the relative distances between the two points. For example, in the figure below if I were to call the point that the total station is one traverse 106 and where the forsight is the next point counter clockwise ( you always throw traverse counter clockwise, this is shown but not said in the figure) traverse 107/101 then I could collect the sets and check realively speeking how close 107 is to 101. The ideal situation is that they have the same coordinates exactly which is never the case. After the closure process. You can use the data collectore to basically distribute all the error in this ring throughout the ring and make a super accurate set of control points. Finally I would use the equation (n-2)180 and if the angle is withing (+-) some relatively small angle difference, then the traverse loop has good closure. For example on this one below we have six angles

(6-2)180degrees=720degrees 

Therefore if the angle was 720degrees00'05" then I would definitely keep it because this traverse has good closure.

In order to do this I will need a data collector. Here is an advertisement that shows the whole process of traversing and also could be a good data collector to buy

Traversing by Repetition With the RECON Data Collector - YouTube

I think we need to get a data collector as well as the other equiptment that I have put on the Surveying equipment order.

 

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