Understanding Face Left and Face Right Angles
Hello all
Probably worth apologising before hand for what may appear to be extremely simple questions – but I am very new to surveying with little access to field equipment.
I am trying to understand face left and face right observations using a total station.
I have done a little sketch which I was hoping someone could confirm that my thinking is correct or if its not then explain why my thinking is incorrect.
Below is a sketch of 3 x points in the ground.
I have set my instrument to face left.
I have set up over STN3 and set a fixed bearing of 00 00 00 to STN2.
I then turn clockwise until I meet STN1 giving me a face left angle of 353 18 14.
(Face Left Image)
Hopefully this is all correct so far.
The next bit is where I get a little confused.
My instrument is still at STN3 and I am sighting to STN1.
In order to take a face right angle I rotate the telescope vertically 180 degrees, making it point in the opposite direction to STN1.
I then turn clockwise until I sight to STN1 and read off the angle, in this case I get an angle of 173 18 13 which is my face right angle.
(Face Right Image)
Would you all agree that this is correct?
The reason why I mention this is because I thought that a face left angle is an angle measured clockwise while at STN3 From STN2 To STN1.
And a face Right angle was when the same angle is measured but telescope is rotated 180 degrees, turned clockwise until you have sighted back to STN1 and then the same angle is measured again but anti-clockwise – I know this is incorrect but doubt has crept into my mind.
Finally the reason why we take angles in both faces is because we can cancel out any errors; in this case I get a face left angle of 353 18 14.
By rotating the telescope 180 degrees so it is pointing in the opposite direction effectively means that my face left angle is now 353 18 14 – 180 = 173 18 14.
While the telescope has been rotated 180 degrees I sight back to STN1, then if the angular reading I get is more or less then 353 18 14 then the difference is the amount of angular error in my observation – would you guys agree?
Just to put everyone’s mind at ease, I am not a surveyor or an engineer hence the “low level” questions, I just have an opportunity to learn about surveying which I hope will lead me onto a job.
If anyone can help then that would be great.
Many Thanks
SS
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