Transcript Document

Raster Analysis
Learning Objectives
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Develop an understanding of the
principles underlying lab 4
Introduce raster operations and
functions
Show how raster analysis can be
applied to topographic surfaces
Raster Data
Derived Data
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By taking rasters and operating
on them we can create
additional data
inRaster * 2 = outRaster
Slope(inRaster) = outRaster
Creating New Data With
Rasters
Digital Elevation Model
Slope Model
Raster analysis
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Typically 4 steps
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Base data
Derived data
Classified data
Combined data
Reclassifying raster
data
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One reason is to set specific values to
NoData to exclude them from analysis.
Another reason is to assign values of
preference, priority, sensitivity, or similar
criteria to a raster.
Operations
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Boolean (AND, OR, NOT, XOR)
Arithmetic (+,-,*,/)
Mathematical (trig, log, etc.)
Logical (<,>,=,<>,etc.)
Overlay
Derivation
Transformation
Boolean (AND, OR, NOT, XOR)
Boolean And
Boolean Or
Arithmetic (+,-,*,/)
Arithmetic (+,-,*,/)
Raster Calculator
Working with NoData
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Similar to logical values, NoData (Null) values also
influence the evaluation of expressions.
This special value indicates that there is no
information associated with the cell.
In general, a Map Algebra
expression will return
NoData for a cell if any of the
corresponding input cells
have NoData.
Functions
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Local
Global
Focal
Zonal
Local
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Very simple
Operate on each
cell individually
Arithmetic and
boolean are
examples of Local
functions
Global
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Perform operations based on an
entire input grid
E.g. Global statistics
Focal
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Evaluates a new grid by
summarizing statistics in the
neighborhood around each cell.
Filters
Low-pass filter
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Also referred to as a mean filter
Low-pass filter
DEM
Low-pass filter
High-pass Filter
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Also referred to as edge enhancement
High-pass filter
DEM
High-pass filter
Additional Filters
Zonal
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Operations
based on zones
of like values in
a grid
Zonal geometry
Zonal stats
Zonal
Input
Output
Recap
Distance
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Euclidean
Rectilinear
Weighted
Weighted Distance
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Sometimes
referred to
as cost
path or
travel cost
Surface Analysis
Derivatives
Slope
Aspect
Hillshade
• Feature Interpolation
- Interpolate Shape
- Interpolate Poly To Patch
- Surface Length
- Surface Spot
- Contour
• Visibility
- Viewshed
- Line of Sight
• Volume
- Surface Volume
- Cut Fill
- Surface Difference
- Polygon Volume
- Extrude Between
Slope: steepness
Aspect: direction of steepest slope
Hillshade: steepness and direction
relative to light source
Slope
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Slope is calculated as the maximum rate of
change in values between each cell and its
neighbors.
Slope may be expressed as either degrees (e.g.,
45 degrees) or percent (e.g., 50%).
Measures of slope in degrees
can approach 90 degrees and
measures of slope in percent
can approach infinity.
Aspect
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The cell values in an aspect grid are compass
directions ranging from 0 to 360.
North is 0 and in a clockwise direction, 90 is
east, 180 is south, and 270 is west.
Input grid cells that have 0
slope (flat areas) are
assigned an aspect value
of -1.
Hillshade
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Hillshading creates a
hypothetical illumination
of a surface by setting a
position for a light source
and calculating an
illumination value for each
cell based on the cell's
relative orientation to the
light, or based on the
slope and aspect of the
cell.
Viewshed
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The viewshed identifies the cells in an
input raster that can be seen from one
or more observation points or lines.
Each cell in the output
raster receives a value
that indicates how
many observer points
can see the location.
Target
181
156
Elevation
206
231
Line of Sight
Observer
0
75
150
Distance
225
300
345
Volume Below Plane
Summary
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Most of the power of the Spatial Analyst
is found within Map Algebra.
The Raster Calculator is your friend.
You can construct a extremely complex
Map Algebra expression using this
interface