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isoband: An R package to generate contour lines and polygons.

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LICENSE.md
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r-lib/isoband

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CRAN statusR-CMD-checkCodecov test coverage

Generate contour lines (isolines) and contour polygons (isobands) fromregularly spaced grids containing elevation data. Package originallywritten by Claus Wilke and donated to r-lib in 2022.

Installation

Install the latest official release from CRAN via:

install.packages("isoband")

Install the current development from github via:

# install.packages("pak")pak::pak("r-lib/isoband")

Examples

The two main workhorses of the package are the functionsisolines()andisobands(), respectively. They return a list of isolines/isobandsfor each isolevel specified. Each isoline/isoband consists of vectors ofx and y coordinates, as well as a vector of ids specifying which sets ofcoordinates should be connected. This format can be handed directly togrid.polyline()/grid.path() for drawing. However, we can alsoconvert the output to spatial features and draw with ggplot2 (seebelow).

library(isoband)m<-matrix(c(0,0,0,0,0,0,1,2,1,0,0,1,2,0,0,0,1,0,1,0,0,0,0,0,0),5,5,byrow=TRUE)isolines(1:ncol(m),1:nrow(m),m,0.5)#> $`0.5`#> $`0.5`$x#>  [1] 4.00 3.50 3.00 2.50 2.00 1.50 1.50 1.50 2.00 3.00 4.00 4.50 4.00 3.75 4.00#> [16] 4.50 4.00#>#> $`0.5`$y#>  [1] 4.50 4.00 3.75 4.00 4.50 4.00 3.00 2.00 1.50 1.25 1.50 2.00 2.50 3.00 3.50#> [16] 4.00 4.50#>#> $`0.5`$id#>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1#>#>#> attr(,"class")#> [1] "isolines" "iso"isobands(1:ncol(m),1:nrow(m),m,0.5,1.5)#> $`0.5:1.5`#> $`0.5:1.5`$x#>  [1] 2.50 2.00 1.50 1.50 1.50 2.00 3.00 4.00 4.50 4.00 3.75 4.00 4.50 4.00 3.50#> [16] 3.00 3.00 3.25 3.50 3.00 2.50 2.50#>#> $`0.5:1.5`$y#>  [1] 4.00 4.50 4.00 3.00 2.00 1.50 1.25 1.50 2.00 2.50 3.00 3.50 4.00 4.50 4.00#> [16] 3.75 3.25 3.00 2.00 1.75 2.00 3.00#>#> $`0.5:1.5`$id#>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2#>#>#> attr(,"class")#> [1] "isobands" "iso"

The functionplot_iso() is a convenience function for debugging andtesting.

plot_iso(m,0.5,1.5)

The isolining and isobanding algorithms have no problem with largerdatasets. Let’s calculate isolines and isobands for the volcano dataset,convert to sf, and plot with ggplot2.

library(ggplot2)suppressWarnings(library(sf))#> Linking to GEOS 3.10.2, GDAL 3.4.2, PROJ 8.2.1; sf_use_s2() is TRUEm<-volcanob<- isobands((1:ncol(m))/(ncol(m)+1), (nrow(m):1)/(nrow(m)+1),m,10*(9:19),10*(10:20))l<- isolines((1:ncol(m))/(ncol(m)+1), (nrow(m):1)/(nrow(m)+1),m,10*(10:19))bands<- iso_to_sfg(b)data_bands<- st_sf(level=1:length(bands),geometry= st_sfc(bands))lines<- iso_to_sfg(l)data_lines<- st_sf(level=2:(length(lines)+1),geometry= st_sfc(lines))ggplot()+  geom_sf(data=data_bands, aes(fill=level),color=NA,alpha=0.7)+  geom_sf(data=data_lines,color="black")+  scale_fill_viridis_c(guide="none")+  coord_sf(expand=FALSE)

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isoband: An R package to generate contour lines and polygons.

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MIT
LICENSE.md

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