LOCAL OPERATIONS

# LOCAL OPERATIONS - some systems allow a full range of...

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LOCAL OPERATIONS produce a new layer from one or more input layers the value of each new pixel is defined by the values of the same pixel on the input layer(s) o neighboring or distant pixels have no effect note: arithmetic operations make no sense unless the values have appropriate scales of measurement (see Unit 6) o you cannot find the "average" of soils types 3 and 5, nor is soil 5 "greater than" soil 3 Recoding using only one input layer examples: 1. assign a new value to each unique value on the input layer o useful when the number of unique input values is small 2. assign new values by assigning pixels to classes or ranges based on their old values o e.g. 0-499 becomes 1, 500-999 becomes 2, >1000 becomes 3 o useful when the old layer has different values in each cell, e.g. elevation or satellite images 3. sort the unique values found on the input layer and replace by the rank of the value o e.g. 0, 1, 4, 6 on input layer become 1, 2, 3, 4 respectively o applications: assigning ranks to computed scores of capability, suitability etc.
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Unformatted text preview: some systems allow a full range of mathematical operations o e.g. newvalue = (2*oldvalue + 3)2 Overlaying layers an overlay occurs when the output value depends on two or more input layers o many systems restrict overlay to two input layers only examples: 1. output value equals arithmetic average of input values 2. output value equals the greatest (or least) of the input values 3. layers can be combined using arithmetic operations o x and y are the input layers, z is the output o some examples: z = x + y z = xy z = x / y 4. combination using logical conditions o e.g. if y>0, then z = y , otherwise z = x o note: in many raster packages logical conditions cannot be done directly from input layers must first create reclassified input images so that cells have 0 if they do not meet the condition and 1 if they do 5. assign a new value to every unique combination of input values o e.g.LAYER 1 LAYER 2 OUTPUT LAYER 1 A 1 1 B 2 2 A 3 2 B 4...
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## This note was uploaded on 12/04/2011 for the course GEB 1011 taught by Professor Staff during the Fall '08 term at Broward College.

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