Cellbased Modeling

1
Cell-based Modeling

• Whats needed to calculate an output value for
  each cell?
• A cell value.
• The manipulation being applied.
• Which other cells need to be included?

2
Cell-based Modeling

• Five types of functions associated with
  cell-based modeling.
• Local functions (work on single cells).
• Focal functions (cells within a neighborhood).
• Zonal functions (cells within zones).
• Global functions (cells within the raster).
• Application functions (combined in a series).

3
Cell-based Modeling

• Local cell functions do not depend on neighbors.
• Focal functions depend on values from a specified
  neighborhood shape, e.g., slope.
• Zonal functions depend on values from
  neighborhoods without specific shape.

4
Cell-based Modeling

• Global functions compute an output raster dataset
  in which the output value at each cell location
  is potentially a function of all the cells in the
  input raster datasets.
• Euclidean distance (distance from the closest
  source cell) ((x1 - x2)2 (y1 - y2)2)1/2 .
• Weighted (cost) surface.
• Shortest path.

5
Detour
6
Zone Definition
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Zone Definition

• Any two or more cells with same value is a zone.
• They can be connected or disconnected.
• If connected they usually represent a single
  feature.
• Each group of connected cells within a zone is a
  region.

8
Zone Definition Attribute Table
9
Application Functions

• Density creates a normalized surface.
• Surface generation interpolates a continuous
  surface.
• Surface analysis manipulates surface data, e.g.,
  DEM to produce new data layers.

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Application Functions

• Hydrologic analysis surface shape/water flow.
• Geometric transformation to match a coordinate
  system.
• Generalization to smooth noisy data.
• Resolution changes to make one raster match
  another.

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Cell-based Modeling/NoData

• The case of NoData.
• Every cell location in a raster has a value
  assigned to it. Where we have no information we
  assign an arbitrary value or NoData.
• Computation of an expression with NoData.
• Return NoData for the location no matter what.
• Ignore NoData and compute with available values.

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Cell-based Modeling/NoData
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Cell-based Modeling/NoData

• Local function output will be NoData.
• Focal function default is to compute with
  remaining values. NoData override.
• Zonal function default is to compute with
  remaining values. NoData override.

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Cell-based Modeling/NoData

• Euclidean distance NoData is ignored except for
  source cells, but output raster will contain
  NoData.
• Weighted (cost) surfaces NoData is a barrier to
  computation and NoData will be returned. Must
  have valid values for source cells.