Index
Map Pairs Analysis Tools II
Crosstabulation
A-Z
Map Pairs Analysis Tools IV
EXTRACT - Querying zones


Boolean Operations

In this part of the tutorial you will meet some techniques you are already acquainted with from our 1st example - methods to query information across different layers and pre-conditions.

  1. AND-Operation
    From a vegetation map (TAURVEGE) and a digital elevation model (TAURDEM) show me all areas with vegetation class 6 in the height range from 1700 to 1800 m a.s.l. (don't be confused about the irregular shaped region)

    TAURVEGE
    TAURDEM
    TAURVEGE-Image
    TAURDEM

    that means, we are interested in those areas that show class 6 and are found between 1700 - 1800 m. So how should we proceed?

    1. RECLASSify TAURVEGE to a boolean image, one that consists of one's for our areas of interest (in this example all patches with class 6) and zero's in all other areas. I will use the function ASSIGN instead. ASSIGN requires us to create a values file, through which we tell the rule for reclassification. So call EDIT / Values file and name the new file CLASS6, let it be integer and write just one line:

         6  1

      ASSIGN asks for the feature definition file - that's the one to be recoded - TAURVEGE, a values file - CLASS6 and an output name - again CLASS6. Don't be afraid about overwriting: the values file has an extension different from the image ones:

      CLASS6
      just class 6 from TAURVEGE

    2. We stress RECLASS to extract the 1700 - 1800 m heights band from our DEM:

      DEM1718
      just heights 1700 - 1800 from TAURDEM

    3. with OVERLAY we multiply CLASS6 by DEM1718 to RESULT, so only locations (cells) with a value of 1 in both images will survive:
      RESULT
      just heights 1700 - 1800 from TAURDEM

    The same result could be achieved by the minimum function in OVERLAY (TOMLIN: LocalProduct).

  2. OR-Operation
    From a vegetation map (TAURVEGE) and a digital elevation model (TAURDEM) show me all areas with vegetation class 6 in the height range from 1700 to 1800 m a.s.l. or areas with class 16 in the same height distribution

    1. we do not need to repeat all the steps from example 1 in that chapter, so a short note will be enough: through the same operations as in 1 we can prepare a result2 image whose areas lie in the 1700 - 1800 range plus showing vegetation class 16. To fulfill the or-rule, we simply use the and- or the maximum-option in OVERLAY to combine result and result2. That's all folks!

Index
Map Pairs Analysis Tools II
Crosstabulation
A-Z
Map Pairs Analysis Tools IV
EXTRACT - Querying zones

last modified: | Comments to Eric J. LORUP idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis idrisi resource center idrisi gis idrisi gis