View
218
Download
1
Embed Size (px)
Citation preview
CS 128/ES 228 - Lecture 4a 2
What is a spatial model?
A simplified representation of part of the real world, referenced to spatial coordinates, and created for a specific purpose
CS 128/ES 228 - Lecture 4a 3
What do you see out the window?
Naïve view: a blur of colors on my retina
Topological view: a collection of points, lines & areas in geometric relation to each other
Object-oriented view: sidewalks, buildings, trees, people …
Western NY view: a lot of snow
CS 128/ES 228 - Lecture 4a 6
What areare data? Observations or measurements of the real world
Three “modes” (or 3 questions to answer):
1. Spatial mode (where is it?)
2. Thematic mode (what is it?)
3. Temporal mode (when was it observed?)
CS 128/ES 228 - Lecture 4a 7
Model dimensionality: 2-D
X-Y coordinates
No elevations
Road crossings…
CS 128/ES 228 - Lecture 4a 9
More sophisticated 3-D models
Wire frame model“draped” withaerial photographor other surfacefeature
Thematic material can be layered on
CS 128/ES 228 - Lecture 4a 10
Model dimensionality: 4-D
X-Y-Z coordinates + temporal dimension
Fig. 7. A geographic information system representation of glacier shrinkage from 1850 to 1993 in Glacier National Park. The Blackfeet Jackson glaciers are in the center. The yellow areas reflect the current area of each glacier; other colors represent the extent of the glaciers at various times in the past. Courtesy C. Key, USGS and R. Menicke, National Park Service
CS 128/ES 228 - Lecture 4a 11
Stages of development:
1. Conceptual model: select the features of reality to be modeled and decide what entities will represent them
2. Spatial data model: select a format that will represent the model entities
3. Spatial data structure: decide how to code the entities in the model’s data files
CS 128/ES 228 - Lecture 4a 14
1. Conceptual models
Decide the model’s purpose
Select the features to be modeled
CS 128/ES 228 - Lecture 4a 15
Spatial entities: 5 types
1. Points
2. Lines
3. Areas (polygons)
4. Networks
5. Surfaces
CS 128/ES 228 - Lecture 4a 17
Discrete vs. continuous features
Points
Lines
Areas
Networks
Discrete features: Continuous features: Surfaces
CS 128/ES 228 - Lecture 4a 18
Networks
Line entity
Used to model features along which material, energy, or information flow
Special components: nodes, stops, turns, direction, impedance
CS 128/ES 228 - Lecture 4a 20
Surfaces
Continuous feature
Every location has a value, even if only interpolated from discrete samples