Intro to IDRISI

1
Intro to IDRISI

• First Look

2
Next Week

• Put your data into digital form
• Excel to IDRISI
• Do some simple operations
• Try some different ways of symbolizing the data

3
The RASTER of raster systems

• A raster is a
• table like array of values
• a grid of cells or pixels
• This is a 6x5 (C,R) ARRAY
• Cells can have different attributes

Symbolization of the attribute values
4
The Raster

• The Geographic position is determined by the
  location of the cell in the raster
• Row 1 Column 5 (R1C5 or, sometimes, C5R1)
• The attribute data is the single numeric value
  stored in the cell
• The raster image has an extension of .rst
• The metadata is in a document file associated
  with the image file and has an extension of .rdc
• BOTH files have to be present. If no .rdc file
  then IDRISI cannot even find the image

5
Navigation in the grid

• To get around in a grid or raster you have to
  know
• Column and row address AND/OR
• X and Y distances
• How do you know X and Y?
• Because X and Y max and min AND cell size are
  part of the data set!
• X min (cell size cells) X (roughly)

6
Addressing, Column, Row
6x5 Grid
C0
C1
C2
C4
C3
C4
R0
R1
R2
R3
R4
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Addressing, R,C (C,R)
A 6x5 grid (C,R format)
C0
C1
C2
C4
C3
C5
R0
0,0
R1
R2
R3
5,4
R4
8
Addressing, X,Y
C0
C1
C2
C4
C3
C4
R0
R1
R2
R3
R4
9
Coordinate Systems in IDRISI
Since Row and Column counts start at 0 The NUMBER
OF rows or columns in the image is always 1 more
than the maximum values. OR A r5,c6 image has max
row 4 and max column 5!
Booby Trap!
10
IDRISIs
Data Type File Type
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Data Types

• Data Type according to IDRISI is the type of
  data which IDRISI will find in the file - what
  IDRISI sees
• Integers are whole numbers within the range -
  32768 to 32767.
• Real numbers have a fractional part, or are whole
  numbers outside the integer range.
• Byte values are positive integer numbers ranging
  from 0 to 255.

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File Type

• File type is the kind of file format used by
  the computer what the computer system sees
• Image (map) files may be stored as ASCII, Binary,
  or Packed Binary,
• Vector files are Binary,
• Attribute Values files are ASCII or ACCESS
  (database)
• DO NOT GET FILE TYPE AND DATA TYPE CONFUSED!

13
Attribute Data Categories

• Data types
• Nominal
• Ordinal
• Interval
• Ratio
• When we do analysis -- Boolean (1,0) later....

14
Metadata

• The who, what, where, when, how and why of data
  set creation
• The document file - .rdc or .vdc
• Very, very important.
• First it contains the information that describes
  the image.
• Second, it keeps references for others to use.
• Third, it tells people how you created/changed
  data

15
Creating New Images?

• You should think about --
• Data Type
• Nominal, ordinal, ratio, interval
• Classification system -- Legend
• What do you want to do with the data?
• Data Entry -- Coding Rules
• Be Consistent
• Why you chose that method

16
Coding rules
?

• Point
• Majority
• Average
• Prominence
• Connective

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OK, Symbolization

• Or
• How is data seen
• By
• Us

18
Layer Symbolization

• How we explain and illustrate...
• What it is
• Where it is
• What is important and significant about it
• To others and to ourselves

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Two Methods

• Graphic (Viewing on screen or on paper)
• Charts, Maps, Displays, Symbols, etc
• Visual! -- intuitively makes sense when you look
  at it
• You can see the spatial relationships
• Descriptive
• Statistics, Narratives

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The Spatial Model

• A graphic of how the process was carried out

• Check the Syllabus for complete description

21
Or an IDRISI model
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Various Ways
Booby Trapalways select first

• Using the modeler (previous slide)
• Using the Calculator

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Various Ways

• Using the modeler (previous slide)
• Using the Calculator
• Using the scalar (this case) dialog

24
Symbolization

• Using color, shapes, style, and size to
  represent or symbolize the data
• Initially we will concentrate on the use of color
  to represent numeric values
• The relationship between value and color in a
  given pallet can have a large effect on the
  communication of the data to you and any other
  viewer.

25
Color Palettes in IDRISI

• What is a palette
• An index that relates the presented color of a
  pixel to an attribute value

0 1 2 3 4 5 -------
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Color Palettes in IDRISI

• What is a palette
• An index that relates the presented color of a
  pixel to an attribute values

• Range of colors in palettes (how many colors)
• 2, 16, 256 or any number lt 256
• The human eye can only discern about 16 different
  colors when they are not close in location

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16 Color problem
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Using IDRISI16 display which has symbols for
values 0 through 15 Any values gt 15 are given
the symbol for 15, In this case dark green.
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Arrangement of Colors

• Qualitative palettes have sharp contrast between
  each symbol in the array
• Black to Yellow to Blue to Orange
• Great for Nominal and Ordinal Data
• Discrete Values
• Quantitative palettes have ramped colors
• Dark to Light
• Great for Ratio and Interval data
• Continuous Values

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Quan256 palette applied to continuous, ratio data
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Qual256 applied continuous, ratio data is ugly!!!
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Qual256 palette applied to discrete, nominal data
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Qual256 palette applied to discrete, nominal data
very hard to read!
34
Orthographic View
Soils draped on elevation
BUT Expanded images by 5 so are 320x320
otherwise you could not see the pattern