GEOG 379 Lecture Notes - Lecture 15: Cartesian Coordinate System, 2.5D, Viewshed
27 Apr 2018
School
Department
Course
Professor
GEOG 379 Lecture Notes
Week 15
4/25 – Basics of 3D GIS
What is 3D GIS?
• An extension of 2-D GIS, with an additional dimension for height or elevation
• Extends GIS capability to build, visualize, and analyze data in three dimension
• Good for applications requiring elevation or depth of earth surface
• Can also be applied for temporal analysis
Application of 3D GIS
• Engineering design of mines, quarries, dams, etc.
• Geological/geophysical exploration
• Scientific explanation of 3D processes such as ocean currents or lava flows
• Visual analysis of any new development in a city
• Perform visibility or viewshed analysis
2D, 2.5D, 3D, and 4D GIS
• Two-dimensional (2D): based on Cartesian coordinate system, limited to representation of data
on planar surface
• Two and one half-dimensional (2.5D): qasi 3-D representation through the use of surfaces or
terrain through (x, y) and attribute values
• Three-dimensional (3D): extends to include a volume element in 3D space
• Four-dimensional (4D): an additional dimension for time; show processes that occur in nature
and through time
Digital Surface/Terrain Model (DTM)
• 2.5D surfaces are also referred to as Digital Terrain Model (DTM)
• Raster format with cell values for additional dimension (z-variable) representing height variation
• Any other cell values can also be converted to DTM: temperature, visual assessment, etc.
Spatial Interpolation
• Predicting value at unknown locations based on dispersed sample points with known value is
called Spatial Interpolation
• Broadly two types –
o Local estimations: gives priority to local influence
o Global approximation: uses all values in the grid; gives more smooth surface
Triangulated Irregular Network (TIN)
• The TIN model represents a surface as a set of contiguous, non-overlapping triangles
• It consists of nodes containing z-values, connected by edges to form triangular facets
• TIN can be created (interpolated) from point, line, or polygon themes
• TINs are usually created from a combination of vector data sources –
find more resources at oneclass.com
find more resources at oneclass.com
