PATTERNS

reclassify raster

These methods purposefully reclassify the values in a raster.

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Boolean raster

This pattern asks a true or false question about each value in the input raster and returns a 1 if true and 0 if false in the corresponding pixel of the output raster.

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graph LR
  input[image]
  method(".gt()") ;
  output[/"image_boolean"/]  ;
  arg1["number"]  ;

  input --> method
  method --> output
  arg1 --o method


  classDef in-out fill:#FFFFFF,stroke-width:1px,stroke: #000000, color:#000000; 
  classDef op fill:#000000,stroke-width:0px,color:#FFFFFF;
  classDef arg fill:#CCCCCC,stroke-width:0px,color:#000000;


  class input in-out; 
  class method op;
  class output in-out;
  class arg1 arg;

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var image_boolean = image.gt(number);  

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The table below lists some of the common methods to ask true or false questions about a raster. Each takes a number as an argument. Some technical folks will use the verb threshold to describe methods that use greater than or less than methods to produce boolean rasters.

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METHOD	DESCRIPTION
.eq(), .neq()	Equal to, not equal to
.gt() .gte()	Greater than, greater than or equal to
.lt() .lte()	Less than, less than or equal to

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Reclassify by equal intervals

This method assigns raster values into equal interval classes. The method divides each value in a raster by the interval number and then rounds down to the nearest integer (finds the floor). The integers in the output are ordinal but arbitrary class numbers.

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---

graph LR
  method("geo.iReclass.equalInterval()") ;
  output[/"image_reclassified"/]  ;
  arg1["image"]  ;
  arg2["interval"]  ;

  method --> output
  arg1 --o method
  arg2 --o method

  classDef in-out fill:#FFFFFF,stroke-width:1px,stroke: #000000, color:#000000; 
  classDef op fill:#000000,stroke-width:0px,color:#FFFFFF;
  classDef arg fill:#CCCCCC,stroke-width:0px,color:#000000;


  class method op;
  class output in-out;
  class arg1 arg;
  class arg2 arg;

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var image_reclassified = geo.iReclass.equalInterval(image, interval);

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Remap old values to new values

This method assigns integer values in the input raster to new integer values in the output raster based on transition rules defined by two lists. The first list defines the set of original values in the input raster. The second list defines the set of new values to be stored in the output raster. The order of the two lists determines the transition. The two lists must be the same length (have the same number of values).

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graph LR
  input["image"] ;
  method(".remap()") ;
  output[/"image_remapped"/]  ;
  arg1["[original values]"]  ;
  arg2["[new values]"]  ;

  input --> method  
  method --> output
  arg1 --o method
  arg2 --o method

  classDef in-out fill:#FFFFFF,stroke-width:1px,stroke: #000000, color:#000000; 
  classDef op fill:#000000,stroke-width:0px,color:#FFFFFF;
  classDef arg fill:#CCCCCC,stroke-width:0px,color:#000000;

  class input in-out;
  class method op;
  class output in-out;
  class arg1 arg;
  class arg2 arg;

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var image_remapped = image.remap(
    [0,1,2,3,4],            // Original values
    [1,0,0,0,1]             // New values 
    )                       // Lengths of two lists must be equal.
  ;

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