Week 9 - Terrain

Question 1

Terrain analysis define

Answer 1

• deals with topography
• DEM
• 3rd dimension: z value
• can be applied to ither data with z values

Question 2

Data for Terrain analysis

Answer 2

• LiDAR (Elevation)

- contours (vector)

Question 3

LiDAR-derived surfaces can also be used to extract feature heights from 2D data. T/F

Answer 3

T

Question 4

Three LiDAR derived raster models

Answer 4

• Digital terrain model (DTM): A bare-earth terrain surface created using ground returns only.
• Digital surface model (DSM): A first-return surface that represents a
“shrink-wrapped” surface of the earth, including buildings, trees, and
other obstructions.
• Normalized digital surface model (nDSM): The difference between
the DSM and DTM surfaces, or a DSM normalized to the bare-earth
surface. Can be used to calculate the height of buildings, trees, or other
features

Question 5

DEM

Answer 5

• any digital representation of a topographic surface
• centre cell
• 30m cell size

Question 6

TIN

Answer 6

• Vector data model
• land surface represented by triangles
• Elevation values (z values) + xy coordinates stored at nodes

Question 7

DEM vs TIN

Answer 7

• can be converted to each other
• TIN is flexible with input data sources–> can add elevation points at precise locations and add breaklines (i.e roads)
• TIN slower to compute
• DEM is fixed with a given cell size–> cannot add new sample data to increase surface accuracy
• DEM is most efficient for terrain analysis.

Question 8

Common terrain variables

Answer 8

• Height
• slope
• aspect

Question 9

Slope

Answer 9

• Slope identifies the steepest downhill direction for a location on a surface
• rise/run = sqrt(b^2+c^2)

Question 10

Aspect

Answer 10

-Aspect is the compass direction that the sloping
surface faces at each location
- It identifies the down slope direction from each cell
to its neighbours.
- aka slope direction
- It is measured clockwise in degrees from 0 (due
north) to 360 (again due north), coming full circle

Question 11

aspect uses e.g

Answer 11

find north-facing slopes for ski runs

Question 12

vertical profile

Answer 12

change in elevation along a line

Question 13

3D draping

Answer 13

Superimpose data such as satellite imagery, hydrographical features, land
cover, vegetation, roads, etc on the perspective view to make it more realistic
- need DEM and TIN

Question 14

Applications of 3D draping

Answer 14

• View shed analysis

- Watershed Analysis

Question 15

Viewshed analysis

Answer 15

• visibility or intervisibility between two or more points

- e.g locating new communications tower–> how visible will it be

Question 16

Problems to use Terrain analysis for

Answer 16

• Monitoring sea level change
• identifying areas/properties subject to flooding
• potential landslide areas