Title: GIS Data Models
1(No Transcript)
2GIS Data Models
- Vector Data Models
- Vector File Formats
- Raster Data Models
- Raster File Formats
3Data Abstraction
- To use GIS the real world must be abstracted into
points, lines, polygons, raster cells, and
attribute values - Class examples may use common object that most
people will understand. If you understand how to
abstract common objects you will be able to apply
the same method to object in your field
4What is Vector Data
- Vector Data uses Points and their (X,Y)
coordinates to represent spatial features - Points, Lines and Polygons
5Points
- A point is a 0 dimensional object and has only
the property of location (x,y) - Points can be used to Model features such as a
well, building, power, pole, sample location ect. - Other name for a point are vertex, node, 0-cell
6Lines
- A line is a one-dimensional object that has the
property of length - Lines can be used to represent road, streams,
faults, dikes, maker beds, boundary, contacts
etc. - Lines are also called an edge, link, chain, arc,
1-cell - In an ArcInfo coverage an arc starts with a node,
has zero or more vertices, and ends with a node
7Figure 4.3 p58 Bernhardsen
8Polygons
- A polygon is a two-dimensional object with
properties of area and perimeter - A polygon can represent a city, geologic
formation, dike, lake, river, ect. - Other name for polygons face, zone 2-cell
- Scale matters
9(No Transcript)
10Data Abstraction Discussion
- If you do not understand this the rest of GIS
will not make sense - Scale Matters
- Intended use Matters
11Examples
12Topology
- A set of rules on how objects relate to each
other - Major difference in file formats
- Higher level objects have special topology rules
13Topology Definition
- The Science of mathematics of relationships used
to validate the geometry of vector entities, and
for operations such as network tracing and tests
of polygon adjacency. - The study of geometric properties that do not
change when the forms are bent, stretched or
under go similar geometric transformations.
14Figure 2-9 GIS Fundamentals, Bolstad
15Planer Enforcement
16Why Topology Matters
- Error Detection
- open polygons
- unlabeled polygons
- slivers
- polygons that cannot exist next to each
- other
- Network Modeling
17Show Placitas
- Arc Node Topology
- Cover
- Lpoly and Rpoly
- Tnode fnode
- Label errors
18Higher Level Object
- Regions
- Networks
- TIN Triangulated irregular network
- Dynamic Segmentation
19Regions
- Overlapping areas with different attributes
- Fire history
- Disconnected areas with the same attributes
- Hawaii
20Networks
- Road systems, power grids, water supply sewerage
systems, drainage network - Continuous connected networks
- Rules for displacement in a network
- Attribute value accumulations due to
displacements
21TIN
- Vector Surface Model
- Triangulated Irregular Network
- A set of nonoverlapping triangles each with a
constant gradient - A TIN can honor original input elevations
22Dynamic Segmentation
- Combines a line coverage with a linear reference
system - Has event tables for point events and linear
events
23Fig 3.13 p52 Chang
24Examples and Demo
25 Shape Files
- Nontopological
- Advantages no overhead to process topology
- Disadvantages polygons are double digitized, no
topologic data checking - 3 files .shp .shx .dbf
26Coverages
- Original ArcInfo Format
- Directory With Several Files
- Database Files are stored in the Info Directory
- Uses Arc Node Topology
- Planer Enforcement
- Connectivity
- Adjacency
27GeoDatabase
- New GIS Format at ArcGIS 8.0
- Three Types
- Personal Geodatabase
- Microsoft access 2000 database
- File Geodatabase
- XML based file
- SDE GeoDatabase
- Multi-user
- Can connect to many RDBMS
- Oracle, SQL server, Informix
- File are stored in the format native to the RDBMS
28Box 3.5 Geographic Information Systems, Chang 04
p. 55
29GeoDatabase
- Shapes are similar to shape files
- Object-oriented model not a Geo-relational
- There are 26 topology rules than can be used to
relate different layers
30Raster Data Model
31Figure 31 Getting Started with Geographic
Information Systems, Clarke (2003) p. 91
32Grid Properties
- Each Grid Cell holds one value even if it is
empty. - A cell can hold an index standing for an
attribute. - Cell resolution is given as its size on the
ground. - Point and Lines move to the center of the cell.
- Minimum line width is one cell.
- Rasters are easy to read and write, and easy to
draw on the screen.
33(No Transcript)
34(No Transcript)
35Raster Pyramids
- With out pyramids the entire raster must be read
for each screen draw - Pyramids store reduced resolution dataset files
.rrd to increase the speed of screen draws - When you add a raster to ArcMap if pyramids do
not exist you can create them
36Raster Resampling
- Nearest Neighbor
- Closest cell
- Continuous and Discrete data
- Bilinear interpolation
- Average of nearest 4 cells
- Continuous data only
- Cubic Convolution
- Average of nearest 16 cells
- Continuous data only
37Quad Tree Compression
- May be use to get variable resolution for imagery
in the National Map
38What are Terrains?
- New Dataset for ArcGIS 9.2
- They are a Multi-resolution, Tin-based surface.
- Comprised of mesurements stored as features in a
geodatabase. - Terrains live inside Feature Datasets, in a
geodatabase.
39What are Terrans?
- Two Main characteristics of Terrrains
- Feature classes participate in a terrain
- Rules are established to generate TIN pyramids
on-th-fly. - They are designed to handle mass volumes of point
data in a logical and efficient storage
mechanism.
40Figure 4.35 Geographic Information Systems and
Introduction, Bernhardsen (2001), p. 87
41C. Dana Tomlin, Geographic Information Systems
and Cartographic Modeling (1990), P. 44
- Yes raster is faster, but raster is vaster, and
vector just seems more corrector
42Images are a form of raster data
- ArcGIS can use many common image formats
43(No Transcript)
44(No Transcript)
45(No Transcript)
46(No Transcript)
47Industry Standard Data Models
- Some Industries have created standard data models
- It is a good idea to use a standard model to
promote sharing of data - Some data models can be very complex
- Complex models require custom tools to be useful
48(No Transcript)
49References
- Getting Started with Geographic Information
Systems 4th Edition, Clark (2003) - Geographic Information Systems an Introduction
3rd Edition, Bernhardsen (2002) - Introduction to Geographic Information Systems
2nd Edition, Chang (2004) - GIS Fundamentals, Bolstad (2002)
- ArcGIS 8.3 Desktop Help
- Using GRID with ArcInfo version 7 ESRI