Angles II Flashcards
What does face left and face right allow us to do?
Neutralise a lot of the errors introduced due to observation errors and incorrectly calibrated instruments.
How can you tell if an instrument is on face left?
Because the vertical circle would be on your left.
How do you change face?
Turn the telescope through 180 degrees and flip the instrument 180 degrees through the horizontal.
What is the observation procedure?
Select face left: Sight A, Sight B,C,X,Y,Z, Sight A again (check).
Change instrument to face right: Sight A, Sight Z,Y,X,D,C,B, Sight A again (check).
What are the rules about FL and FR?
Face left- swing right (clockwise)
Face right- swing left (anti-clockwise)
What is a round of angles?
A set of face left and face right readings and it is the minimum at any station.
How do you eliminate errors?
Change face and take the mean angles from pairs of observations to eliminate errors in;
1) Dishevelment of instrument (residual error)
2) Trunnion axis tilt
3) Collimation error (line of sight)
What should the difference be between Fl and FR reading?
180 degrees different.
What should you never do during a round of observations?
Re-level the plate bubble its ok before you start a new round.
How do you prevent reading error and circle graduation error?
Change the horizontal zero.
What is the difference between vertical angle and zenith angle?
A traditional Vertical angle is measured up or down from horizontal, it ranges from -90° below horizontal (depression) to +90° above (inclination) a Zenith angle is measured from the upper end of the vertical line continuously all the way around.
Are these errors; instrumental, natural or personal?
1) Theodolite or TS out of adjustment
2) Take means of FL and FR
3) Calibrate the instrument regularly (every 6 month in heavy use).
Instrumental
Are these errors; instrumental, natural or personal?
1) Strong winds
2) Sunshine
3) Refraction
Natural
Are these errors; instrumental, natural or personal?
1) Poor centring over the survey mark
2) Poor pointing at the target
3) Plate bubble not central
4) Turning wrong screws and clamps at wrong time
5) Misreading circles or display
6) Best to make quick, decisive observations
Personal
