Transcript Raster Analysis 1

ESRM 250 & CFR 520: Introduction to GIS
Raster Analysis 1
ESRM 250/CFR 520
Autumn 2009
Phil Hurvitz
© Phil Hurvitz, 1999-2009
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ESRM 250 & CFR 520: Introduction to GIS
Overview
Raster layers
Setting raster layer and analysis properties
Raster function types
Performing raster analysis
Map Algebra
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ESRM 250 & CFR 520: Introduction to GIS
Overview
Raster layers
Setting raster layer and analysis properties
Raster function types
Performing raster analysis
Map Algebra
© Phil Hurvitz, 1999-2009
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ESRM 250 & CFR 520: Introduction to GIS
Raster layers: Overview
Raster layer types
Raster layer properties
Adding raster layers to views
Displaying raster layers
Examining cell values in raster layers
Managing raster layer files
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Raster layers: Overview
“Grid” layers are ArcView's implementation of
the basic raster data model.
environmental
data are
represented as
“grid” raster
layers
(image from ESRI)
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Raster layers: Overview
Grid layers are ArcView's implementation of the
basic raster data model.
rectangular tessellation of
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square cells
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Raster layers: Overview
Grid layers are theoretically different from image
layers
Grids and images are stored in the same basic
(raster) format: a rectangular matrix of cells
where each cell has a value
Image layers always represent remotely sensed
imagery (e.g., digital orthophoto)
Grids typically represent other continuous
phenomena (e.g., slope, salinity)
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Raster layers: Overview
All images are rasters.
All grids are rasters.
NOT all rasters are
images or grids
rasters
grids
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images
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Raster layers: Overview
Grid layers are different from image layers
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These are image layers
reflectance
values
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Raster layers: Overview
Grid layers are different from image layers
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These are grid layers
elevation
etc. values
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Raster layers: Overview
Grid layers are different from image layers
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Raster layers: Overview
Grid layers are different from image layers
cells
have
numerical
value that
represent
a numerical
variable
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Raster layers: Overview
Raster layers are suited for representation of
phenomena that vary gradually over space
e.g. elevation,
wind speed,
or slope
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Raster layers: Raster types
Only integer rasters can have layer tables
integer (no decimals)
floating-point
(decimals)
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Raster layers: Raster types
Only integer rasters can have layer tables
will not have a table
will have a table
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Raster layers: The spatial analyst
All raster layer functionality occurs through the
Spatial Analyst extension.
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Loading of raster
layers for analysis
Raster analysis
Spatial analyst must be enabled
to perform raster analysis
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Raster layers: Raster layer properties
Layer description contains a lot of information
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Raster layers: Raster layer properties
Layer description contains a lot of information
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Raster layers: Raster layer properties
Layer description contains a lot of information
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Raster layers: Adding raster layers to views
Add raster layers in the same way as adding
other data sets
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Raster layers: Displaying raster layers
Usually numerically classified
Symbology can be altered like other layers
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Raster layers: Examining cell values with histogram
Histograms describe structure of data values
Y-axis: cell
counts in each
value class
X-axis: values
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Raster layers: Examining cell values with identify tool
Individual cell values can be identified as with
feature data
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Raster layers: Examining cell values with queries
Integer rasters can be queried in the usual way
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Selected sets/cells shown in cyan
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Raster layers: Managing raster layer data files
Raster data sources should always be managed
by ArcCatalog
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copying
moving
renaming
deleting
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Overview
Raster layers
Setting raster layer and analysis properties
Raster function types
Performing raster analysis
Map Algebra
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Setting raster analysis properties
Analysis properties determine spatial properties for
all newly created output raster layers
Analysis properties:
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Working directory
Analysis mask
Analysis extent
Cell size
Once set, analysis
property values
stay set until
changed
[Settings described below]
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Setting raster analysis properties: working directory
Working directory specifies the default location
for new rasters created with the Spatial
Analyst Extension
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Setting raster analysis properties: Analysis extent
Analysis extent sets the spatial properties for
output of analyses
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Extent is a
rectangular area
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Setting raster analysis properties: Analysis extent
Be careful about setting extent; it may cause
poor raster-to-raster registration
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Setting raster analysis properties: Analysis extent
Be careful about setting extent; it may cause
poor raster-to-raster registration
Use “snap extent to”
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Setting raster analysis properties: Cell size
Analysis cell size sets the raster cell size for output
of analyses
Use consistent cell size
for analysis of multiple
raster data sets
Note:
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small cells → larger files (-)
small cells → longer processing (-), but …
small cells → usually greater accuracy (+)
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Setting raster analysis properties: Masking
Analysis mask defines “valid data extent” of
output rasters
A mask can have any shape (whereas analysis
extent is always rectangular)
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Setting raster analysis properties: Masking
Analysis mask defines “valid data extent” of
output rasters
“mask_grid” has a specific
extent of valid data (in green)
output matches the same
data extent
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ESRM 250 & CFR 520: Introduction to GIS
Overview
Raster layers
Setting raster layer and analysis properties
Raster function types
Performing raster analysis
Map Algebra
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Raster function types
Local functions
Global functions
Zonal functions
Focal functions
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Raster function types: Global functions
Local functions apply an independent calculation
to all input raster cells
Each output cell’s value is calculated
independently
local sine
e.g. sin(12) = -0.537
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Raster function types: Global functions
Global functions apply a calculation considering
all cell values
the value 3 is calculated by
knowing that flow comes from
other cells
the value 5 is calculated by
knowing that flow comes from
other cells, cumulatively
e.g. flow accumulation
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Raster function types: Zonal functions
Zonal functions apply one calculation to all input
raster cells within each zone
zones are defined as a group of cells having the same value
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Raster function types: Zonal functions
Zonal functions apply one calculation to all input
raster cells within each zone
zonal sum
for zone 1:
(53 + 57 + 33 + 78 + 31 + 12 + 32 + 9 + 9 + 33 + 76) = 423
all cells in zone 1 in the output are given value 423
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Raster function types: Focal functions
Focal functions apply one calculation to all input
raster cells within a “focus”
focal mean
(27 + 8 + 22 + 16 + 21 + 16 + 6 + 44 + 8) / 9  18.7
The “focal” cell in the output grid is given value 18.7
© Phil Hurvitz, 1999-2009
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ESRM 250 & CFR 520: Introduction to GIS
Overview
Raster layers
Setting raster layer and analysis properties
Raster function types
Performing raster analysis
Map Algebra
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ESRM 250 & CFR 520: Introduction to GIS
Raster analysis: calculations across multiple rasters
Multi-raster analyses are possible because of
spatial registration
multiple raster layers
share the same X,Y
coordinate space
cell values are calculated
across multiple raster
layers
to create a single
output raster layer
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Raster analysis
Analyses are performed using GUI tools
Spatial Analyst toolbar > Raster Calculator
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Raster analysis
Analyses are performed using GUI tools
ArcToolbox tools
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Raster analysis
Many more raster analyses are available through
the Raster Map Algebra syntax, which can be
used in the Raster Calculator or custom tools
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Overview
Raster layers
Setting raster layer and analysis properties
Projections and raster layers
Raster function types
Performing raster analysis
Map Algebra
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Raster analysis: Map algebra (or “How it works”)
Raster layers may be used in arithmetic
expressions in the raster calculator
output_data_set = input_raster1 operator
input_raster2 ...
e.g.,
slp_dem = slp_raster
output
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input 1
*
dem
operator
input 2
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Raster analysis: Map algebra (or “How it works”)
Raster layers may be used in algebraic functions
in the raster calculator
output_data_set =
function (input_data_set[s]{,arguments})
e.g.,
slp_raster = slope (dem, percentrise)
output
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function
input 1
input 2
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Performing raster analysis: Using rasters in math
Map algebra is calculated with the
Raster Calculator
raster layers
operators
operator
classes
expression
box
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Raster analysis: Map algebra (or “How it works”)
Map Algebra arithmetic:
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Calculation =
(dem greater than 500 and dem less than 1000 )
Logical (Boolean) criteria
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Raster analysis: Map algebra (or “How it works”)
Map Algebra arithmetic:
0 = false
1 = true
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Raster analysis: Map algebra (or “How it works”)
Map Algebra function:
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Calculation = mosaic([q1822], [q1823])
Mosaics two rasters
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Raster analysis: Map algebra (or “How it works”)
Map Algebra function:
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