Hawth's Analysis Tools for ArcGIS

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 Summary

SPATIAL REPLACE TOOL
Input: a thematic (categorical) raster layer
Output: a new raster layer
Features:

  • replaces cell values in a raster layer by assigning the closest permitted alternative value
  • provides a method of removing unwanted categories from a raster layer by assigning new values based on a simple neighborhood analysis, rather than a reclassification
  • works on any size/shape of patch in the raster (i.e. works equally well for linear classes like roads, pipelines or rivers as it does for large patches like cutblocks, agricultural fields, etc)
  • allows the user to interactively define the set of acceptable replacement values

Limitations:

  • processes only one band of the raster
  • replaces only one value at a time (to replace multiple values, the tool would have to be run once per value)


[Click for larger view]

 Example

Figures A, B & C. In this example two values in the original raster (A) are replaced. Those two values represent roads (bright red cells in A) and cutblocks (orange cells in A). Because the tool replaces one value at a time, it has to be run twice to accomplish this. Th first time the tool is run, roads are replaced by any other non-water feature (B). The second time it is run, cutblocks are replaced by any other forest type (we know that if it was cut it had to be forested at one time, therefore it would not make sense to allow cutblock cells to be replaced with Grassland or Water values). The final result is shown in C.

 Help

Getting started. A raster layer must be loaded into ArcMap in order to use this tool. If you wish to run this tool on a multi-band image, you must load the bands into ArcMap separately, and run the tool on each one.

Priority of replacement values. This tool begins by examining the 8 cells immediately surrounding the cell that is being spatially recoded. If there are any acceptable replacement values among these 8 cells, it will select the lowest value (even if another higher value is in majority). If there are no suitable replacement values in these 8 cells, the tool moves out by one cell, and so on, until an acceptable replacement is found.

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