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| − | [[Category:Projects]]
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| − | [[Category:Hydrology in R]]
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| − | ===The topographic index===
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| − | Some GIS programs can calculate the topographic index, but the package provides a function too. If you use the R function, you should delineate your catchment in your preferred GIS application and export a DEM of your catchment as a text file (ascii). Pixels outside the catchment area should be given a distinct value that can be set to NA in R.
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| − | For now, the GIS functions of this package are quite limited. The DEM has to be imported as a matrix, which can then be processed by topidx(). Take for instance this minimalistic DEM, saved in a test file called "DEM.txt". Values outside the catchment are given the value -9999 (this can be any other value):
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| − | -9999 -9999 828.9 835.6 -9999
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| − | 818.3 826.0 830.7 834.5 836.0
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| − | 817.1 824.0 825.2 833.3 836.9
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| − | 816.5 820.0 824.1 330.8 -9999
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| − | 810.7 815.6 822.2 -9999 -9999
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| − | This file can be imported and processed in R with:
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| − | DEM <- read.table("DEM.txt")
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| − | DEM <- as.matrix(DEM)
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| − | remove the values outside the catchment:
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| − | DEM[DEM==-9999] <- NA
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| − | plot the DEM:
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| − | image(DEM)
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| − | calculate the topographic index:
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| − | topindex <- topidx(DEM, resolution=25)
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| − | Split the values into a set of classes, for instance for use with topmodel():
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| − | topidxclasses <- make.classes(topindex,16)
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