Heighting I

Question 1

What is the importance of heighting? (4)

Answer 1

1) To provide height or contours on a map or plan
2) Cross-sections and profiles- depth of river beds
3) Provide a level or inclined surface- house foundations
4) Monitoring deformations- such as bridges, dams & volcanoes.

Question 2

Define Heighting.

Answer 2

It is the process of determining heights of points above or below a reference datum. Concerned with measurements of the differences in heights between points.

Question 3

What is spirit levelling?

Answer 3

Defines a horizontal plane using a spirit level and

place a long ruler at the two points and measure the change in height.

Question 4

What is trigonometric heighting?

Answer 4

Uses a total station rather than a level and we measure the vertical angle and the slope distance. This creates a right-angle triangle therefore allowing us to use trig where we can calc the height.

Question 5

What are the advantages and disadvantages of spirit levelling?

Answer 5

Very accurate and cost-efficient but individual legs have limited range.

Question 6

What does a theodolite and total station measure?

Answer 6

Angles of elevation/depression and slope distance.

Question 7

What are the advantages and disadvantages of trigonometric heighting?

Answer 7

flexible method and longer range than spirit levelling but requires greater care than a spirit level.

Question 8

When do you need to account for effects of earth curvature and refraction?

Answer 8

When >300m because the centre of gravity will start to converge.

Question 9

What is barometric heighting?

Answer 9

Uses a barometer to measure differences in pressure. where height difference is proportional to air pressure.

Question 10

What are the limitations of barometric heighting?

Answer 10

It has the lowest accuracy.

Question 11

Define vertical line.

Answer 11

The line in the direction of gravity, e.g. freely suspended plumb line.

Question 12

Define horizontal line.

Answer 12

Line perpendicular to gravity at a point.

Question 13

Define level surface.

Answer 13

Surface (line) that is everywhere perpendicular to gravity, but gravity varies from point to point so not a plane and not regular, therefore it approximates the ellipsoid of rotation.

Question 14

Define horizontal plane.

Answer 14

Plane perpendicular to gravity at any point. Tangential to level surface at that point.

Question 15

Define datum surface.

Answer 15

Any level surface to which heights are referred.

Question 16

What is mean sea level (MSL) an example of?

Answer 16

An example of a level surface once tidal effects are accounted for.

Question 17

Define Ordnance datum (OD).

Answer 17

Datum surface used by OS since 1920.

Question 18

Define a benchmark.

Answer 18

Reference mark for which the height above a selected datum surface is known.

Question 19

Define reduced level.

Answer 19

Height referred to a defined datum.

Question 20

Define a Geoid.

Answer 20

MSL of the Earth. This is if the oceans completely covered the Earth then the Geoid is the shape the oceans would take if you eliminated all wind effects.

Question 21

What are the characteristics of fundamental benchmarks? (4)

Answer 21

1) Very few (approx 180) spread throughout the entire UK.
2) Established by geodetic levelling
3) Comprise a buried chamber contained two reference points.

Question 22

What are the characteristics of flush bracket benchmarks? (3)

Answer 22

1) More numerous that fundamental BM’s
2) Located at intervals of every 1.5km
3) Used on OS Triangular pillars, bridges & older buildings.

Question 23

What are the characteristics of Cut benchmarks? (2)

Answer 23

1) Most common

2) Approximately size (0.1x0.1m), V shaped horizontal bar (reference mark).

Question 24

What are the characteristics of bolt benchmarks? (2)

Answer 24

1) Much less common

2) Sometimes used on rooftops or piers.

Question 25

What is the essential equipment when levelling? (3)

Answer 25

1) Level which defines a horizontal line of sight
2) Levelling staff- provides a graduated scale
3) Change plate- provides firm base for levelling staff on soft ground.

Question 26

What do older engineers refer levels as?

Answer 26

Dumpy level

Question 27

What is a tilting level?

Answer 27

You tilt this in the correct horizontal position every line of sight you measure.

Question 28

What is the tilting level sequence of operation? (9)

Answer 28

1) Set up tripod
2) Attach level and centre circular bubble
3) Focus cross-hair
4) Point at the staff
5) Focus the telescope
6) Centre fine bubble
7) Read staff (lowest reading when rocked)
8) Point at new staff position
9) Repeat from “focus telescope”

Question 29

What is the most common level now?

Answer 29

Automatic

Question 30

How can you tell if the level is automatic?

Answer 30

Shake and you should hear the compensator rattle.

Question 31

What is the automatic level sequence of operation? (8)

Answer 31

1) Set up tripod
2) Attach level and centre circular bubble
3) Focus cross hairs
4) Point at the staff
5) Focus the telescope
6) Read the staff (lowest reading when rocked)
7) Point staff at new position
8) Repeat from “Focus telescope”

Question 32

What is a digital level?

Answer 32

Does everything for you, you can point this at the levelling staff, press a button and it will automatically read the staff for you.

Question 33

What has a digital level got in it?

Answer 33

Essentially a camera built into the optics and takes a photo of the levelling staff and you can digital process that therefore a lot quicker.

Question 34

What is a laser level?

Answer 34

It is a laser that goes up the line of gravity through the pentaprism and gets turned out at 90 degrees and the whole instrument spins around creating a horizontal plane. it will beep when you are at the correct position on the staff.

Question 35

What are the two types of staff?

Answer 35

1) E-staff

2) Bar code staff but this is for digital levels to read

Question 36

What is an advantage for a laser level?

Answer 36

You can have multiple people working on sight with the same level.