Difference between revisions of "Calculating the topographical index"

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-[[Category:Projects]]
-[[Category:Hydrology in R]]
-===The topographic index===
-Some GIS programs can calculate the topographic index, but the [[Topmodel]]-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.
-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):
-   -9999 -9999 828.9 835.6 -9999
-.3 826.0 830.7 834.5 836.0
-.1 824.0 825.2 833.3 836.9
-.5 820.0 824.1 330.8 -9999
-.7 815.6 822.2 -9999 -9999
-This file can be imported and processed in R with:
-   DEM <- read.table("DEM.txt")
-   DEM <- as.matrix(DEM)
-remove the values outside the catchment:
-   DEM[DEM==-9999] <- NA
-plot the DEM:
-   image(DEM)
-calculate the topographic index:
-   topindex <- topidx(DEM, resolution=25)
-Split the values into a set of classes, for instance for use with topmodel():
-   topidxclasses <- make.classes(topindex,16)

Latest revision as of 09:04, 9 November 2009