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3D and Surface/Terrain Analysis. Prepared by:. George McLeod. With support from:. NSF DUE-0903270. in partnership with:. Geospatial Technician Education Through Virginia’s Community Colleges (GTEVCC). . D. Digital Terrain Models.

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3d and surface terrain analysis

3D and Surface/Terrain Analysis

Prepared by:

George McLeod

With support from:

NSF DUE-0903270

in partnership with:

Geospatial Technician Education Through Virginia’s Community Colleges (GTEVCC)

digital terrain models

D

Digital Terrain Models
  • A digital terrain model is a model providing a representation of a terrain relief on the basis of a finite set of sampled data
  • Terrain datarefers to measures of elevation at a set of points V of the domain plus possibly a set E of non-crossing line segments with endpoints in V
data sampling
Data Sampling
  • Regular
  • Irregular
our three primary terrain models
Our three Primary terrain Models
  • Digital Elevation Models (DEMS) – aka Regular Square Grids (RSGs)
  • Triangulated Irregular Networks (TINS) – aka Polyhedral terrain models
  • Contour Maps – aka “topo” maps
the data

TIN

The Data…

DEM

LIDAR (LIght Detection And Ranging)

introduction to the data
Introduction to the Data
  • Terrain mapping
  • Land surface is 3-D
  • Elevation data or z-data is treated as a cell value or a point data attribute rather than as a coordinate.
slide8

Digital Elevation Model (DEM)

    • Gridded array of elevation points obtained from a variety sampling methods
slide9

D

DEMs

A constant function can be associated with each square (i.e., a constant elevation value). This is called a stepped model (it presents discontinuity steps along the edges of the squares)

slide10

The function defined on each square can also be a bilinear function interpolating all four elevation points corresponding to the vertices of the square

slide11

Triangulated Irregular Network (TIN)

    • Series of non-overlapping triangles
    • Elevation values are stored at nodes
    • Sources: DEMs, surveyed elevation points, contour lines, and breaklines
    • Breaklines are line features that represent changes of the land surface such as streams, shorelines, ridges, and roads
slide12
TINs
  • Example of a TIN based on irregularly distributed data
data for terrain mapping and analysis
Data for Terrain Mapping and Analysis
  • Triangulated Irregular Network (TIN)
    • Not every point in DEM is used
    • Only points most important
    • VIP (Very Important Points) algorithm
    • Maximum z-tolerance algorithm
    • Delaunay triangulation: all nodes are connected to their nearest neighbor to form triangles which are as equi-angular as possible.
tins vs grids
Needs larger storage capacity

Computationally difficult

Flexibility of data sources

Can add points

Better display

More efficient

Needs smaller storage capacity

Computationally simpler

Fixed with a given cell size

Cannot add sample points

Raster display

Less efficient

DEM

TIN

Tins vs. Grids
contour mapping
Contour Mapping
  • Contouring is most common method for terrain mapping
  • Contour lines connect points of equal elevation (isolines)
  • Contour intervals represent the vertical distance between contour lines.
  • Arrangement of contour lines reflect topography
slide16

Digital Contour Maps

Contours are usually available as sequences of points

A line interpolating points of a contour can be obtained in different ways

Examples: polygonal chains, or lines described by higher order equations

slide17

Digital Contour Maps: properties

They are easily drawn on paper

They are very intuitive for humans

They are not good for complex

automated terrain analysis

contour profile mapping
Contour Profile Mapping
  • Vertical profile shows changes in elevation along a line, such as a hiking trail, road or stream.
cartographic terrain mapping
Cartographic Terrain Mapping
  • Hill shading is also known as a shaded relief or simply shading
  • Attempts to simulate how the terrain looks with the interaction between sunlight and surface features.
  • Helps viewers recognize the shape of land-form features on a map.
hillshading
Hillshading
  • Four factors control the visual effect of hill-shading
    • Sun’s azimuth is direction of incoming light (0 to 360°)
    • The sun’s altitude from horizon (0-90°)
    • Surface slope (0-90°)
    • Surface aspect (0 to 360°)
hypsometric tinting
Hypsometric Tinting
  • Hypsometric tinting
    • Applies different color symbols to represent elevation or depth zones.
methods of analysis
Methods of Analysis
  • Slope measures the rate of change of elevation at a surface location
  • Aspect is the directional measure of the slope (degrees- 4 or 8 directions)
  • Hillshade, refer to previous slides
  • Line of sight refers to the straight line visibility from an observer to a feature
  • Viewshed analysis refers to the areas of the land surface that are visible from an observation point or points.
  • Watershed analysis refers to an area that drains water and other substances to a common outlet.
  • Area andvolume calculations
connectivity function example viewshed analysis
Connectivity Function Example:Viewshed Analysis

Image Source: Chrisman, Nicholas.(2002). 2nd Ed. Exploring Geographic Information Systems. p 198. fig. 8-14.

hillshade
Hillshade

Setting a hypothetical light source and calculating the illumination values for each

cell in relation to neighboring cells. It can greatly enhance the visualization of a

surface for analysis or graphical display.

Azimuth 315°, altitude 45°

viewshed
Viewshed
  • Viewshed identifies the cells in an input raster that can be seen from one or more observation points or lines.
  • It is useful for finding the visibility. For instance, finding a well-exposed places for communication towers

hillshaded DEM as background

application environmental impact analysis
Application: Environmental Impact Analysis

3D landscape model impact on natural beauty

application flood risk
Application - Flood Risk

3D height data changing water levels-danger areas

the 3 rd dimension height analysis combining several methods together
The 3rd Dimension: Height Analysis – combining several methods together
  • Contours
  • Hill shading
  • Spot height symbols
  • Cliff & slope symbols
  • Viewpoint symbols
3d terrain analysis summation
3D Terrain Analysis: Summation
  • GIS does not always provide exact answers to problems, but by identifying trends based on geography, GIS can reveal patterns that can help us make informeddecisions.
  • A GIS can improve decision-making; it cannot make decisions for us.