Transcript GIS Functions - University of Arizona

GIS Functions and Operators
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The functions associated with raster cartographic
modeling can be divided into five types:
Those that work on single cell locations (local functions
or operators)
 Those that work on cell locations within a neighborhood
(focal functions)
 Those that work on cell locations within zones (zonal
functions)
 Those that work on all cells within the raster (global
functions)
 Those that perform a specific application (for example,
hydrologic analysis functions)
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Map Algebra
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Map algebra is a language specifically designed for
geographic cell-based systems and provides the basis
for cartographic modeling.
Based on concepts originally presented by Joe Berry
and C. Dana Tomlin.
Map algebra provides a language to conveying logic
constructs while maintaining the power of the
mathematical base underlying the cell-based
structure.
Map Algebra operators and functions apply
mathematical computations on a raster “map” vs.
matrix algebra.
Local Functions
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Local functions apply their calculations to a single cell location before
calculating the next location, until all cells have been processed. To
perform the calculation, the local function only needs to know the values
at the location for a single raster or for multiple rasters, as well as, in
some cases, a comparison value.
Operations or functions can be
applied on single or multiple grids:
output = (inlayer1 + inlayer2) / 2
output = sin(inlayer1)
output = min(inlayer1, inlayer2, inlayer3)
Operators and Functions
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There are three types of operations:
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Arithmetic operators: *, /, -, +
Boolean operators: And, Or, Xor, Not
Relational operators: ==, >, <, <>, >=, <=
Output  ([Inlayer1]  [ Inlayer2]) / 2
Operators and Functions
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Mathematical functions are applied to the values in a
single input raster. There are four groups of
mathematical functions
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Logarithmic
Arithmetic
Trigonometric
Powers
Other local functions compute statistics, combine, or
other operations from a list of multiple inlayers.
Output = min(Inlayer1, Inlayer2, Inlayer3)
Focal Functions
Focal (or neighborhood) functions compute an output grid in which the
output value at each cell location is a function of the input cells in the
specified neighborhood “around” each output (or target) location.
Neighborhoods can be
different sizes and geometries.
Different arithmetic and
statistical functions can be
applied to summarize a
neighborhood values.
Example:
Output = focalsum (Input,
rectangle, 3,3)
Zonal Functions
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Zonal functions compute an output raster dataset where the
output value for each location depends on the value of the cell
at the location and the association that location has within a
cartographic zone.
Output = zonalsum(inlayer, zonelayer)
Output = zonalgeometry(zonelayer, all)
Global Functions
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Global, or per-raster, functions compute an output raster
dataset in which the output value at each cell location is
potentially a function of all the cells combined from the
various input raster datasets. There are two main groups of
global functions: Euclidean distance and weighted distance.
Output from the Euclidean
distance function, each cell
contains the shortest distance to
any input point.
Application Functions
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There are a wide series of cell-based modeling functions
developed to solve specific applications.
There is some overlap in the categorization of an application
function and the local, focal, zonal, and global functions (such
as the fact that even though slope is usually used in the
application of analyzing surfaces, it is also a focal function).
Application functions include the following:
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Density analysis
Surface generation
Surface analysis
Hydrologic analysis
Geometric transformation
Generalization
Resolution altering
Lab 2
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Part 1: Examine Grids
Compute Slope and look at the statistics
 Reclass Slope and compute the area in Zone 5
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Part 2: Locating a Watch Tower (Iron Age II)
Jordan Highlands – Dr. Christopherson PhD
research site
 We will attempt to identify the “watch tower” based
on three factors
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Must be “In View” of the Fort and the Largest City
 Must be located in the highest elevation zone
 Must have either a rectangular or circular structure
 Will Intersect on the three factors to narrow the search
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