Week5: 14 Terrains2

Question 1

The distribution of the sampled data can depend on ..

Answer 1

the acquisition technique or on the specific application

Question 2

Polyhedral Terrain models: properties

Answer 2

1) can be used for any type of sampled pointset (regularly & irregularly distributed)
2) can adapt to the irregularity of terrains
3) represent continuous surfaces

Question 3

The most commonly used polyhedral terrain models

Answer 3

Triangular Irregular Networks (TINs) where each polygon of the domain partition is a triangle

Question 4

TINs: important properties

Answer 4

1) guarantee the existence of a planar patch for each region (triangle) of the domain subdivision (three points define a plane): the resulting surface interpolates all elevation data
2) The most commonly used triangulations are Delaunay triangulations

Question 5

Why Delaunay triangulations?

Answer 5

1) they generate the most equiangular triangles in the domain subdivision (thus minimising the numerical problems e.g. point location)
2) their dual is a Voronoi diagram. Therefore, some proximity queries can be solved efficiently
3) proven that they generate the best surface approximation (in terms of roughness) in 3D independently of the z values
4) several efficient algorithms to calculate them

Question 6

The most commonly used gridded elevation models are ..

Answer 6

Regular Square Grids (RSGs) where each polygon in the domain partition is a square

Question 7

TINs & RSGs

Answer 7

• both models support automated terrain analysis operations
• RSGs are based on regular data distribution
• TINs can be based both on regular and irregular data distribution

Question 8

Digital Contour Maps: properties

Answer 8

1) easily drawn on paper
2) very intuitive for humans
3) not suitable for complex automated terrain analysis

Question 9

An approximate terrain model is ..

Answer 9

a model that uses a subset of the data available