General

leaflet.opacity extends the leaflet R package with the Leaflet.OpacityControls JavaScript plugin (LizardTech 2013). It offers control buttons and a slider for adjusting the opacity of a layer.

Tutorial

This tutorial requires the following packages.

library(leaflet)
library(leaflet.opacity)
library(raster)

To demonstrate leaflet.opacity an artificial raster layer is created with the raster R package.

r <- raster(xmn = -2.8, xmx = -2.79, ymn = 54.04, ymx = 54.05, nrows = 30, ncols = 30)
values(r) <- matrix(1:900, nrow(r), ncol(r), byrow = TRUE)
crs(r) <- CRS("+init=epsg:4326")

The three functions addLowerOpacity, addHigherOpacity and addOpacitySlider add a new control to the leaflet map. They can be used like all leaflet functions together with the %>% operator.

leaflet() %>%
    addTiles() %>%
    addRasterImage(r, layerId = "raster") %>%
    addOpacitySlider(layerId = "raster")

In this example a leaflet map is created with background tiles and the previously created raster layer r is added. The function addOpacitySlider adds the opacity slider to the map. The layerId defines which layer’s opacity is controlled by the slider.

Leaflet map with opacity control in RStudio viewer panel.