Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Surv 130 Exam > Week 10: Land surface modelling > Flashcards

Week 10: Land surface modelling Flashcards

1
Q

3 representations of earths shape

A
  1. Terrestrial surface
  2. Geoid
  3. Ellipsoid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is terrestrial surface in terms of earths shape

A

Earths actual shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is geoid in terms of earths shape

A

Sea level - a complex mathematical estimation of the earths shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is ellipsoid in terms of earths shape

A

Simple mathematical estimation of the earths shape

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

For engineering works we generally consider that we are working on ______ unless we are working on a ______

A

A planar surface,
Very large area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why is there a change in any planar surface across the globe

A

Because of the curvature of the earth, there is no perfectly flat plane on earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Radius of the earth

A

6,371 km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When designing/building over a large area, we would need to determine the

A

Topography: What the existing shape of the land surface is

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are we determining when we look at topographical info

A
  1. The ground surface details in relation to some repeatable measurement system
  2. Northings (y value)
  3. Eastings (x value)
  4. Heights (z value)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

The spatial positions of features are

A

The differences in the X, Y and Z positions between the features

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Surveyors also look at how the topography changes over time. This could be due to

A
  1. Natural process of weathering and erosion
  2. Design where we modify the land surface for a specific purpose
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Reasons that an existing surface would need to be modified

A
  1. Create level playing fields
  2. Provide platforms for construction purposes
  3. Create grades so that stormwater can be directed and collected within a network of pipes
  4. Create access to properties and destinations through a roading network
  5. Removal of trees - Construct rain gardens or bioswales
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How do we collect the information that will allow us to understand the topographical information of the land surface

A
  1. By field surveying methods
  2. By using GPS/GNSS
  3. By using different lazar scanning technologies
  4. Lidar scanning
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does Lidar stand for

A

Light detection and ranging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Field surveying methods process

A
  1. Usage of total stations and prisms
  2. Picks up individual points and measures the change in position and height from the known position
  3. May also be completed by a robotic total station
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

GPS/GNSS methods process

A
  1. Picks up individual points and measures the change in position with a base station set up over it
  2. Or can measure individual points in relation to a wider coordinate system
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Lazar scanning methods process

A
  1. Picks up the reality of the scene that is being looked at by scanning millions of positions relative to each other, creating a dense point cloud
  2. Because the scan picks up so much information, the point cloud needs to be interrogated to get the required information and be geo-referenced into a known coordinate system
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Once the positional data is collected, how do we change it from coordinates (just points) into a useful and usable form

A
  1. We change the data into a representation of the shape of the land surface
  2. This representation is usually a topographical plan that includes all of the height information and features across the site
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

If we were surveying the North Ground, what features would we want to pick up

A

Around the outside: The streets, The kerbs, The widths of the footpaths

Inside the ground: Trees, Clubrooms, Features (lamp-posts, benchs, etc)

And the heights associated with each

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

On a topographic plan, we are looking down onto a surface and this is called

A

The plan view, where all distances are measured in horizontal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How can we represent height information on a topographical plan so that the actual surface information is available in all three dimensions

A
  1. Add height information to every measured point
  2. Use contours (convention heights to a metre or common multiple)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is a contour

A

A line on a map or plan that joins points of equal height above a known datum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Contours depict

A

The relief of the terrain, that is the changes in height that occur across the area of interest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Contour intervals are

A

The vertical distance between level surfaces forming the contours (varies depending on the maps purpose scale and diversity of relief)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is the best way of collecting the position and height information on North Ground

A

Around the outside where all the trees are: A direct method which is suitable for any terrain

On the open field part:
A grid method where points are measured conform to a square or rectangular grid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What would be the danger if we only used a single method of collecting the position and height information

A

We would miss important information and would not be able to display a true representation of the shape of the surface (where field diagrams are really useful)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

When we have collected all of the data, and using appropriate software, we are able to create

A

A digital terrain model (DTM), also sometimes known as a digital elevation model (DEM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

A DEM is a

A

3D representation of continuous variations of relief over an area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Some assumptions need to be made in order for DTM/DEM information to be generated, these include

A
  1. Usage of triangles created between points which develops into a derived triangulated irregular network (TIN)
  2. We assume that all triangle sides have a constant slope
  3. We assume that the surface area of any triangle is a plane
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

The triangles in DTM/DEM are created to

A

Join up the points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

The contours are created by

A

Interpolation along the triangles sides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What additional information is required when creating topographic plans and contours

A

Features such as rivers, streams, and roads, as they are linear topographic features that include uniform slops and extended locations

33
Q

Features such as rivers streams and roads need to use

A

Breaklines (discontinuity lines) to show top of banks, bottom of banks, walls, other roads, etc

34
Q

Breaklines force

A

Triangle sides to from along the feature, creating correct representation of the ground

35
Q

Two methods to improve the look or shape of the surface (terrain)

A
  1. Edit the DEM (underlying information)
  2. Shape or smooth the contour lines
36
Q

Editing of the DEM to improve the look of the surface is done by

A
  1. Swap triangles to change shape of terrain
  2. Delete triangles (skinny ones round edges)
  3. Edit heights of points (small changes)
36
Q

Now that a topographic plan with contours exists, it can be used for analysis of the _____ by looking at _____

A

Shape of the surface (terrain), Different views

36
Q

In civil engineering and development work, the views that we are interested are

A
  1. Plan view
  2. Longitudinal section
  3. Cross section
37
Q

Longitudinal section description

A

A profile taken along the proposed centreline at regular intervals (20m) showing existing ground levels and the possible constructed levels (formation level)

38
Q

Longitudinal sections are used to determine

A
  1. If suitable grades are available along the length of the long section
  2. The difference between the existing ground and the information level
    The difference is known as cut or fill and is dependant on the differences in levels between the surfaces
39
Q

How are suitable grades on a long section calculated

A

By the vertical distance (rise, positive or negative) divided by the horizontal distance (run)

40
Q

Longitudinal sections allow you to find out

A

How much work will be required along the centreline (or other selected position) and determine if the amount of cut or fill is acceptable

41
Q

Longitudinal sections do not show

A

Any RLs outside of the centreline, information is only available for the slice being shown

42
Q

Longitudinal sections are determined and drawn by

A

Establishing the profile that you want to see and then drawing it from the side elevation perspective

43
Q

In longitudinal sections, the profile position is established on

A

The plan view

44
Q

Longitudinal sections follows the line that you won’t be able to see. This means it can be

A

A straight line, a curved line or a mixture of both

45
Q

The long section establishes the horizontal distance along the x axis of a plan and the

A

Corresponding heights on the Y axis

46
Q

In long sections, the existing heights are determined from

A

The contour information on the plan view

47
Q

In long sections, the data panel establishes

A
  1. A datum for the drawing
  2. Provides line spaces so that information about the following is provided at the regular interval positions
48
Q

A datum for the drawing is

A

A position below the lowest level that will be shown on the long section

49
Q

A datum for the drawing allows for

A

The best use of the available space and removes large gaps of no useful info on the plan

50
Q

Formation level

A

The desired height levels along a long section

51
Q

Cut or fill is the difference between

A

The existing ground level and the formation level

52
Q

Having different scales is called a

A

Distorted scale

53
Q

Usually a what scale difference between vertical and horizontal scale and why

A

1:10 scale difference because change in the vertical is generally much less than the distance represented in the horizontal

54
Q

If we used the same scale for both horizontal and vertical, we would not be able to

A

See the changes in elevations and this would hinder our design abilities

55
Q

Anything that appears on the profile line should be shown on the

A

Long section

56
Q

Features that should be shown on the long section if they are on the profile line include

A
  1. Underground services (pipework)
  2. Features on the surface
  3. Features above the surface (may interfere with design work)
57
Q

Cross sections are

A

Profiles that are taken at the same regular intervals as used for the longsection but perpendicular (at right angles) to the centre line

58
Q

Cross sections are used to establish

A
  1. The detail at each of the interval position
  2. The existing ground, in the cross section profile, at each position (comes from the long section)
59
Q

Cross sections are drawn from

A

The centre line position

60
Q

In cross sections, the extent of the construction surface extends out until

A

It meets the existing ground (catch point)

61
Q

Cross sections are needed to

A
  1. Determine the extent of the cuts or fills
  2. Calculate the volume of the earthworks
  3. Volume of earthworks is the total amount of work that needs to be completed
  4. Requires a typical cross section to be created
62
Q

Since we use the plan view and the long section to draw a cross-section, the same assumptions regarding ______ must remain

A

Linear relationships

63
Q

Cross sections are drawn at

A

A suitable natural scale

64
Q

A natural scale means

A
  1. The horizontal and vertical scales are the same
  2. No distortion of the changes in height
65
Q

Why are cross sections drawn at a suitable natural scale

A

In the long section, it is likely that you will never be able to see the entire length of the project so you will never be able to see the full job in front of you

66
Q

What data was collected from the three created views

A

Point position information, x y and z infoTh

67
Q

Having three different drawings is important because

A
  1. They give three different views on seperate drawings and are different representations of the same data
  2. All three views must be used together in order to understand the shape of the surface and allow complete analysis of a project to occur
68
Q

How can the amount of work to be computed be determined from the info contained in the three views

A

We calculate the volume of earth works that will be required for the changes between the surfaces (existing ground and the new surface (formation level))

69
Q

3 things that the plan view provides us with

A
  1. The position of all the topographical features and the spatial relationship between them
  2. Height information through the depiction of contours
  3. Only horizontal distances
70
Q

2 things the longitudinal section provide us with

A
  1. The info of the entire length of the provided shown from a side profile
  2. Horizontal distances and vertical distances, often at a distorted scale to add emphasis to the changes in height
71
Q

2 things the cross-section provide us with

A
  1. The info of a position from a perpendicular position to the centreline
  2. At a natural scale
72
Q

3 things the combination of the three views allow to happen

A
  1. The plan view allows us to establish the shape of the existing surface
  2. The info on the plan view and the long section allows us to create the cross-sections
  3. As soon as we have the cross sections we use the info to calculate volumes
73
Q

The important information is being able to determine an area from the cross-section, and once you have a series of cross-sectional areas you can

A

Calculate the volume

74
Q

Volume between the adjacent cross sections is the

A

Average area of sections x the distance apart (method of average end areas)

75
Q

What does the method of average end areas calculation rely on to be accurate

A

The assumption of the linear relationship between the sections

76
Q

All calculations will be slightly inaccurate, we therefore need to

A

Find out how inaccurate we are and let anyone who is associated with the calculations know that there is an error associated with the value

77
Q

What are some uses for our ability to define and show the shape of surface

A
  1. Investigation
  2. To check the suitability of the site
  3. Design
  4. Calculations
  5. Construction
  6. Perspective
  7. Supervision/monitoring
  8. Effects

Surv 130 Exam (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions