Height Traversing Flashcards
Define vertical control.
Refers to the various procedures used to obtain elevation of point above or below datum, usually where differences in heights are measured.
What are the two basic methods for determining height difference?
1) Spirit levelling
2) vertical angle levelling/trigonometric heightening/height traversing if multiple legs
With aid of a diagram describe spirit levelling?
Measure the difference in height from A to B, levelling instrument itself not set up on A or B.
What is vertical angle levelling also known as?
Trigonometric heighting/levelling.
What is height traversing?
Height traversing is essentially vertical angle levelling but is done when there are a fixed number of points.
When did height traversing become popular?
With the increase in precision of vertical angle reading in total stations.
When is height traversing accurate?
If the distance L is small (approx 200-300m) otherwise must make corrections for earth curvature and refraction.
With the aid of a diagram describe how you calculate the change in height for height traversing?
Draw correct diagram shown on lecture notes and:
ΔHAB = hi + Lsinθ -ht
Vertical angle levelling:single forward ray example: If hi=1.547m, ht=1.429m, slope distance=42.965m, FL ZA=84°24’37’’ and DR ZA=275°34’58’’ hence FL VA= 5°35’23’’, FR VA= 5°34’58’’ and thus reduced mean VA=05°35’11’’ what is the change in height?
ΔH= 1.547+42.956*sin(05°35’11’’)-1.429 = 4.3000m
In a previous question the change in height for a traverse was 4.3000m what is the height difference error (with the same data though as the previous question) the distance is 50mm short ?
Slope distance=42.915 (now)
So:
ΔH= 1.547+42.915*sin(05°35’11’’)-1.429 = 4.2915m
height difference error = 4.2915-4.3000 = -4mm
Describe the height traversing process for a three leg (four station) traverse that has been observed from station A (known height) through unknown stations B and C to station D (known).
1) Vertical angles and slope distances have been measured both ways along each leg.
2) Need to determine the heights of stations B and C.
3) Need to determine the height misclosure of the traverse.
4) Asses the benefit of observing traverse legs both ways.
5) To do this, compute the height differences along the traverse legs and sum.
How do you calculate the height misclosure (forward only)?
High misclosure (forward only)= sum of change in heights forward - “true” height difference.
How do you calculate “true” height difference?
Change in height between the height of the first station and the height of the last station.
How do you calculate the height misclosure (reverse only)?
High misclosure (reverse only)= sum of change in heights reverse - “true” height difference.
How do you calculate the height misclosure (using means)?
High misclosure (using means)= sum of change in height means- “true” height difference.
