Modeling

1
Modeling

• Buffers
• Boolean Logic
• .avl files

2
Overview

• Buffers again
• Logic (Booleans)
• Modeling with sub models
• Area and .avl files
• Grouping

3
Buffers

• Used in both vector and raster GIS
• In IDRISI there is a buffer module that does t he
  job.
• Usually you want the buffer to be a Boolean image
  (1s and 0s) that can then be used in a spatial
  selection process

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Ex 5.3

• It is focused on using Boolean logic to select
  tax parcels that meet criteria like
• Elevation
• Distance from water
• Slope class
• Aspect
• And one of the first things you have to do is
  make a Buffer of 200 feet around all the water.

5
Not as simple as it sounds

• The reason is that all the water layers have a
  background color
• This is a problem since the buffer process
  buffers any non zero cells in the image
• So the water images have to be cleaned up to get
  rid of the background
• Alert ?the image from Ex 5.1 is not correct for
  this exercise

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Buffer Dialog
Streamsnb
200
x
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Buffer output
0,1,0
0,0,1
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In Ex 5

• What you want is the areas that are NOT within
  200 of water
• This is the NOT of the 200 water buffer
• NOT?
• Two ways
• Use the calculator
• Make a NOT submodel

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MULTIPLE OPERATIONS

• If you AND multiple images you get only the areas
  where 1 appears in ALL layers!
• If you OR multiple images you get only the areas
  where 1 appears in more than one image
• If you NOT an image 1 ? 0 and 0 ? 1.

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Truth Table
NOT A Reclass 1?0 0 ? 1 AND Multiply OR
AAD RECLASS 2 ? 1 XOR ADD RECLASS 1 ? 0
2 ? 0
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AND
MULTIPLY
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OR
ADD
RECLASS
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NOT

• Pretty easy
• Reclass 0 to 1 and 1 to zero

NOT
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AND Acceptable areas
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OR Acceptable areas
AOK OR SOK OR EOK OR WOK
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Logical combinations
AOK AND ( SOK OR EOK)
(AOK AND SOK ) OR EOK
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Logical combinations
If you don't get the ( ) right, you won't get
the right answer!
AOK AND ( SOK OR EOK)
(AOK AND SOK ) OR EOK
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Modeling w/ sub models
Sub Model
Application
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Making Submodels

• Some, like AND, OR, NOT will be used a lot
• Others can be left in an exericses workspace
• Put them in NIFKIN
• Create the model to do an AND
• Save it
• Save it as a submodel

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Area and Values Files

• The AREA function has 3 possible outputs
• And 7 possible area measures

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If you chose Values

• Nothing will happen! (that you can see, anyway)
• BUT a values (.avl) file will be made
• Use Edit to view
• In this case there are 1421.875 acres with an
  attribute of 0.

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Just how does area work?

• It computes the total area for all cells with a
  given attribute
• It does NOT compute the area of individual
  clusters or single cells
• And Perimeter works the same way

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Trick
25
Grouping Area
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Grouped w/ diagonals
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Values is a Crummy Format

• Copy and past into Word ?
• Import into Excel if you have to do some
  calculations with the data. ?
• In 5.3 you need to make several imports.
• Copy the LU code and acreage for criteria 1 and
  past it into a worksheet
• In subsequent imports just past the acreage into
  every other column

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ENJOY