2. GIS data models
Model
Abstraction of realworld/process/phenomenon
GIS data model
Set of constructs/rules for
describing or representing
the real world within a
computer
Two data models
Vector
Raster
3. Data Models
Raster
A cellular based data structure composed of rows
and columns for storing images. Homogenous
units are called cells or pixels.
• Mainly Used for representing continuous surface e.g.
reflectivity of EMR, elevation, rainfall, soil/landuse etc.,
Vector
A coordinate based data structure commonly used
to represent geographic features. Homogenous
units are points, lines, and polygons.
• Mostly used for representing discrete geographical
features such as building, wells, roads etc.,
4. A grid defines geographic space as a matrix of
identically-sized square cells. Each cell holds a
numeric value that measures a geographic attribute
(like elevation) for that unit of space.
Source: http://www.ce.utexas.edu/prof/maidment/class.html
5. Grid data structure
Grid size is defined by extent, spacing
and no data value information
Number of rows, number of column
Cell sizes (X and Y)
Top, left , bottom and right coordinates
Source: http://www.ce.utexas.edu/prof/maidment/class.html
6. Definition of a Grid
Cell size
Number
of
rows
NODATA cell
(X,Y)
Number of Columns
Source: http://www.ce.utexas.edu/prof/maidment/class.html
10. Reality >>> Raster value
The average EMR is measured within
each grid
Depending on the average intensity of
the EMR a numeric value is assigned
for each grid
14. Types of Raster
Based on the data type
Integer
• Binary or Boolean (0 or 1)
• Grayscale (Signed/Un-signed, 8 bit, 16bit,
32bit)
Real (floating decimal point)
• Grayscale (32 bit, 64 bit)
Based on the number of bands
Single band
Multi-band Remotely sensed data
31. Data Conversion
Integrate other GIS data with Remote
Sensing
Rasterization
Vector to Raster
Can only approximate original location
• Pixel resolution
Vectorization
Raster to Vector
34. Vectorization
Raster to vector
More complex
• Points
• Lines
• Polygons
Edge enhancement
Classification
Vectorizing
Topology need to be built
Notas del editor
charCharacter or small integer.1bytesigned: -128 to 127unsigned: 0 to 255short int (short)Short Integer.2bytessigned: -32768 to 32767unsigned: 0 to 65535intInteger.4bytessigned: -2147483648 to 2147483647unsigned: 0 to 4294967295long int (long)Long integer.4bytessigned: -2147483648 to 2147483647unsigned: 0 to 4294967295