Gis data models

Chia sẻ: Nguyen Thi Hong Mai | Ngày: | Loại File: PPT | Số trang:70

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After this lecture you should be able to: Describe the primary Vector data models used in GIS and give examples, describe raster data models and give examples, describe TIN data models, explain “topology”, describe the main file formats used in GIS.

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Nội dung Text: Gis data models

Lecture 3: GIS Data Models
AIM: To introduce various GIS data models After this lecture you should be able to: Describe the primary Vector data models used in GIS and give examples Describe raster data models and give examples Describe TIN data models Explain “topology” Describe the main file formats used in GIS
Graphic Features Objects which are shown on a map are called graphic features or features. These features may be natural or man made objects.
Graphic Features Digital representation of physical or man made elements:  Vectors  Points or Nodes  Lines or Arcs  Polygons  Raster Cells or Pixels  Images  Digital Orthophotography
Geographic Data Types  Images  Vector  Raster (GRID)  Attributes  TIN (Triangulated Irregular Network)  Annotation © Paul Bolstad, GIS Fundamentals
Geographic Data Types © Paul Bolstad, GIS Fundamentals
DIGITAL SPATIAL DATA • RASTER • VECTOR • Real World Source: Defense Mapping School National Imagery and Mapping Agency
Electronic Maps in Raster and Vector Formats
Raster Data Sources Air Photos Satellite Imagery Scanned Maps
Digital Orthophotograph A scanned photograph that has been mathematically rectified to eliminate the effects of displacement so that its view always appears as though it is perpendicular to the ground. Image Copyright 1993 Nassau County, NY
Scanned Document
Raster Maps (images)  A set of colored pixels representing chart information as a picture on computer screen  Simply an array of pixels arranged in rows and columns  Pixels are color coded, but do not represent features explicitly  Rasters can have value attached Source: Defense Mapping School National Imagery and Mapping Agency
The Appeal of Raster  Looks like a paper map  Cheap and easy to produce (scan existing paper chart)  Runs easily on PC  World-wide availability w/updates available  Problems:  Datum may or may not be WGS84  Does not allow automated grounding avoidance or any other computer- aided analysis  Storage not as efficient Source: Defense Mapping School National Imagery and Mapping Agency
Vector Data An intelligent form of digital geographic data where real world objects are represented by points, lines and polygons. An objects representation is described by attributes and coordinates. Examples include: Digitized Maps GIS Data Source: Defense Mapping School National Imagery and Mapping Agency
Linking Attributes and Graphics  In addition to Geography, GIS is also about Information. A GIS marries the capabilities of computer mapping with database management systems. So, a geospatial analyst can “click” on a geographic feature and find out information about it. Or, they can query the database to find out information about all the geographic objects that meet a specific criteria.  Information about a geographic object is called an attribute.
Linking Attributes with Graphics  In this example, the user has issued a query to select all the properties whose classification is single family residential (210), and colored the selection red.
Vector Data is Layered •• 2 • Features: • 1 5 Line • Points: • Connected • Lake • 4 Detached • Area •• 7 6 Text Spatial Data Analysis 30ł 30’ N 30ł 30’ N 040ł 40’ E 040ł 50’ E Geographic data are separated into themes, tiled for speed of access and placed on CD-ROM Network Analysis Source: Defense Mapping School National Imagery and Mapping Agency
Paradigm Shift May look “different” from a paper map (software- dependent) Underlying database allows queries and layer selection Zooming reveals detail Complex, expensive, and time-consuming to produce Source: Defense Mapping School National Imagery and Mapping Agency
Raster and Vector Data Models Real World 600 1 2 3 4 5 6 7 8 9 10 1 B G Trees 500 2 B G G 3 B 400 4 BG G Trees Y-AXIS 5 B G G 300 6 B G BK House 7 B 200 8 B B G River 9 B 100 10 B 100 200 300 400 500 600 X-AXIS Raster Representation Vector Representation Source: Defense Mapping School National Imagery and Mapping Agency