GIS and Terrain Modeling Quiz

Introduction to GIS

• Spatial and 3D analysis is the topic of the presentation.

Presentation Outline

• Spatial Analysis:
  • Overlay techniques
  • Proximity analysis
  • Interpolation
  • Euclidean distance
• 3D Analysis:
  • 3D models and DTM surfaces
  • 3D analysis

Spatial Analysis

• GIS as a computerised map can be used to control police vehicles, ambulances, and other emergency services.
• Real-time tracking and route-finding functions in GIS allow controllers to identify the best vehicle for an emergency and provide the fastest route.
• Historical data stored in GIS can be used to analyze incidents, identify black spots, and improve response times.

Overlay Techniques

• Map layers are placed on top of each other.
• Objects within one layer can be selected that lie within another layer to be identified.
• Overlay operations combine layers to create a new layer.

Thematic Overlays

• Different data layers such as social factors, economic factors, transport factors, land use factors, and environmental factors can be overlayed to analysis.

Cont. Overlay for optimum rice growing areas

• Optimum daily rainfall of 10 mm is needed for high rice yields
• Soil type must be sandy loam
• Rainfall and soil type map overlaying can easily reveal the locations for optimum rice production.
• Numeric values can be assigned to both rainfall and soil type, making it easier to identify locations suitable for optimum rice growing.

Cont. Overlay - Results

• Overlay results are accurate based on used data for querying.
• Spatial querying has various application and methods throughout the world.
• GIS provides an efficient way to overlay map layers, potentially discovering correlations or problem-solving solutions that would be impossible by other means.

Proximity Analysis

• Proximity analysis allows creating buffers around selected features with a specified range.
• The area of intersection between buffers is often an area of common interest.
• This technique can be applied to a variety of analysis tasks.

Interpolation

• Interpolation allows creating a surface from point data.
• Point values of concentration/magnitude are used to estimate values across a larger area.

Spatial Interpolation

• A process of creating a surface map from isolated sample points.
• Sample points are locations where data is collected on a specific phenomenon recorded in spatial coordinates.
• Uses mathematical estimations to 'guess' values between those points.
• Output can be raster or vector format.

Eg. Interpolation

• Technique used to interpolate ground water pollution samples.
• The Interpolation surface can be used for generating contour lines.

Eg. 3D interpolated surface

• Image illustrating a 3D interpolated surface.

Euclidean Distance

• Used to identify the nearest point or area of interest, such as a hospital or emergency response centre.
• This method calculates distance to help in emergency response applications.
• Suitable for creating suitability maps.

3D Models and Surface Analysis

• To fully represent real landscapes, 2D representation requires interpretation and imagination.
• The real world is 3D, and conventional maps represent it in 2D.
• GIS has the capacity to create dynamic and appealing 3D maps, which is a benefit.

Height Information

• Mapmakers use visual symbols including contours, spot height symbols, hill shading, cliff and slope symbols, and viewpoint symbols for height representation, creating the illusion of an undulating surface.

Capture of Height Information

• Height information can be captured by recording the heights at different points in an area.
• GIS stores this information as z-values or coordinates in a grid format.
• Z-values represent elevations (height above sea level, usually in meters).

Data Models used for DTM in GIS

• Spot height/LIDAR data
• Contour data
• Grid data
• DEM data

Basic Data Structures for Elevation

• Vector: spot heights/LiDAR data; contour lines.
• Raster: gridded data like DEM.

Raster Elevation Data Structure - Grid

• Raster model divides the world into cells with x-y coordinates.
• DTM in GIS can be effectively generated from gridded data.
• Elevation data is represented digitally in a grid system

Two ways of representing elevation

• Vector contour lines and raster grids

Two ways GIS works with digital elevation data

• Spatial Analyst—2D
• 3D Analyst—3D

Methods of Interpolation Elevation Surface

• TIN (Triangulated Irregular Network)
• Voronoi Diagrams
• IDW (Inverse Distance Weighted)
• Kriging
• Topogrid
• Surf (RST) Regularized Spline with Tension

Developing a DTM (Digital Terrain Model)

• Point height information is collected for the surface.
• Point data is connected to form contour lines to create a terrain profile.
• 3-D data is stored as a grid of points (x, y and z attributes).
• The grid data is used to create a 3-D model.

TIN Surface

• Uses triangles to represent a surface continuously.
• Interconnecting irregular spot heights generates the triangles.
• Triangles form a flat surface internally.

TIN (Triangulated Irregular Network)

3D Surface Analysis

• Create contours from input elevation raster data.
• Contour representation shows elevation variations.

2D Model

3D Modeling

Slope Derivation

Slope Surface analysis

• Slope is derived from elevation dataset using mathematical relationships.
• Slope data is presented in a specific format
• Slope measurements are taken at specific angles in degrees.

Aspect derivation

Aspect Surface analysis

• Aspect analysis measures slope direction based on the compass.
• Aspect is the direction of the slope in degrees measured from North.
• Aspect direction is used in an analysis of the terrain.

Hillshade derivation

Hillshade Surface analysis

• Hillshade analysis determines illumination of a 3D surface.
• A directional light source illuminates the surface.
• Azimuth and Altitude are included in the analysis.

Hill shade surface analysis

• Azimuth is the directional angle of the sun.
• Altitude is the angle of the sun's elevation

Viewshed Surface analysis

• The view from a certain point in the data.

3D model

Buildings and Roads (Perspective Viewing)

Realistic 3D Models

• Adding colours to a 3D model based on maps or aerial photos to make it more realistic.
• Integrating details of objects like buildings, forests and other data as needed.
• This process creates a 3D computer model that represents reality.

Terrain with Spatial Modeling Analysis

• Analysing terrain with aspects like erosion and deposition.
• Studying elevation and rainfall patterns.

Summary

• Using GIS techniques to identify patterns in data, including defining boundaries based on phenomena.
• Using overlay techniques to develop appropriate areas for activities
• Employing proximity and geoprocessing tools for spatial analysis.
• Interpolation methods for accurately determining concentrated values across a surface.
• Using GIS to visualize data in a 3D representation for analysis.

Test your knowledge on Geographic Information Systems (GIS) and terrain modeling techniques. This quiz covers key concepts such as Digital Terrain Models, elevation data structures, and various analysis methods used in spatial modeling. Enhance your understanding of how 3D representations are created and utilized in mapping.