SSN (version 1.1.7)

additive.function: Generate an Additive Function Value

Description

Generate an additive function value based on a proportional influence variable into an additive function value

Usage

additive.function(ssn, VarName, afvName)

Arguments

ssn

a SpatialStreamNetwork-class object

VarName

The name of the the variable that will be used to calculate the additive function value. The data.frame ssn@data must contain a column with this name.

afvName

The name assigned to the column of additive function values, which are added to the ssn@data data.frame object, as well as the data.frames for the observed and prediction sites.

Value

The SpatialStreamNetwork object, ssn, with a new column named VarName included in the data.frames for the lines, observed sites, and prediction sites to hold the AFVs.

Details

Calculating the additive function values (AFVs) is a two step process; first the VarName values are used to calculate the segment proportional influences (PIs). Then the segment PI's are used to calculate the AFVs for each line segment, observed site, and prediction site in the SpatialStreamNetwork-class object. A detailed description of the segment PIs and the steps used to calculate AFVs are provided in Peterson and Ver Hoef (2010; Appendix A). The AFVs can also be calculated using the Spatial Tools for the Analysis of River Systems (STARS), which is a custom ArcGIS (version 9.3.1) toolbox.

References

Peterson, E. E. and Ver Hoef, J. M. (2010) A mixed-model moving-average approach to geostatistical modeling in stream networks. Ecology 91(3), 644--651.

Peterson E.E.(2011)STARS: Spatial Tools for the Analysis of River Systems: A tutorial. CSIRO Technical Report EP111313. 42p.

Examples

library(SSN)
#use mf04p SpatialStreamNetwork object, already created
data(mf04p)
# for examples, copy MiddleFork04.ssn directory to R's temporary directory
copyLSN2temp()
#make sure mf04p has the correct path, will vary for each users installation
mf04p <- updatePath(mf04p, paste0(tempdir(),'/MiddleFork04.ssn'))

#Calculate an additive function value based on an existing column.
names(mf04p@data)
mf04p <- additive.function(mf04p, "h2oAreaKm2", "areaAFV")
#notice that a column called afvArea was already included, and "areaAFV" replicates it
# in the lines data
head(mf04p@data)
# and in the observed points data
head(getSSNdata.frame(mf04p))
# and in the prediction points data
head(getSSNdata.frame(mf04p, "pred1km"))