R packagestarsExtra provides several miscellaneous functions for working withstars objects, mainly single-band rasters. Currently includes functions for:
- Focal filtering
- Detrending of Digital Elevation Models
- Calculating flow length
- Calculating the Convergence Index
- Calculating topographic aspect and slope
Installation
CRAN version:
install.packages("starsExtra")GitHub version:
install.packages("remotes")remotes::install_github("michaeldorman/starsExtra")Documentation
The complete documentation can be found athttps://michaeldorman.github.io/starsExtra/.
Example
The following code applied a 15*15 mean focal filter on a 533*627stars Digital Elevation Model (DEM):
data(carmel)carmel_mean15=focal2( x=carmel,# Input 'stars' raster w=matrix(1,15,15),# Weights fun="mean",# Aggregation function na.rm=TRUE,# 'NA' in neighborhood are removed mask=TRUE# Areas that were 'NA' in 'x' are masked from result)The calculation takes: 0.5625446 secs.
The original DEM and the filtered DEM can be combined and plotted with the following expressions:
r=c(carmel,carmel_mean15, along=3)r=st_set_dimensions(r,3, values=c("input","15*15 mean filter"))plot(r, breaks="equal", col=terrain.colors(10), key.pos=4)
Timing
The following code section compares the calculation time offocal2 in the above example withraster::focal (both using C/C++) and the reference methodfocal2r (using R code only).
library(microbenchmark)library(starsExtra)library(raster)data(carmel)carmelr=as(carmel,"Raster")res=microbenchmark( focal2=focal2(carmel, w=matrix(1,15,15), fun="mean", na.rm=FALSE), focal=focal(carmelr, w=matrix(1,15,15), fun=mean, na.rm=FALSE), focal2r=focal2r(carmel, w=matrix(1,15,15),mean), times=10)res#> Unit: milliseconds#> expr min lq mean median uq max neval#> focal2 542.3506 546.0164 587.9224 554.3557 609.8761 793.5663 10#> focal 114.3561 115.9764 142.2213 119.7932 125.9327 339.7064 10#> focal2r 17236.5407 17367.5100 17734.2765 17634.1378 17902.5663 19048.0060 10boxplot(res)