Extend Layers Control in Leaflet Map

This function extends an existing layers control in a leaflet map by adding custom views, home buttons, opacity controls, and legends. It enhances the functionality of a layers control created with leaflet or leaflet.extras.

Usage

extendLayersControl(
  map,
  view_settings,
  home_btns = FALSE,
  home_btn_options = list(),
  setviewonselect = TRUE,
  opacityControl = list(),
  includelegends = TRUE
)

Arguments

map

A leaflet or mapview object to which the extended layers control will be added.

view_settings

A list specifying the view settings for each layer. Each list element should contain either:

• coords: A vector of length 2 (latitude, longitude) for setting the view, or length 4 (bounding box: lat1, lng1, lat2, lng2) for fitting the bounds.

• zoom: The zoom level (used for setView).

• fly (optional): A logical indicating whether to use flyTo or flyToBounds instead of setView or fitBounds.

• options (optional): Additional options to pass to setView, fitBounds, or flyTo.

home_btns

Logical. If TRUE, adds a "home" button next to each layer name in the layer control. Clicking the home button zooms the map to the view specified for that layer in view_settings.

home_btn_options

A list of options to customize the home button appearance and behavior. Possible options include:

• text: The text or emoji to display on the button (default is '🏠').

• cursor: CSS cursor style for the button (default is 'pointer').

• class: CSS class name for the button (default is 'leaflet-home-btn').

• styles: Semicolon separated CSS-string (default is 'float: inline-end;').

setviewonselect

Logical. If TRUE (default) sets the view when the layer is selected.

opacityControl

A list specifying the opacity control settings for each layer. Each list element should contain:

• min: Minimum opacity value (default is 0).

• max: Maximum opacity value (default is 1).

• step: Step size for the opacity slider (default is 0.1).

• default: Default opacity value (default is 1).

• width: Width of the opacity slider (default is '100%').

• class: CSS class name for the slider (default is 'leaflet-opacity-slider').

includelegends

Logical. If TRUE (default), appends legends to the layer control. Legends are matched to layers by their group name. The legends need to be added with corresponding layer IDs.

Value

A modified leaflet map object with extended layers control including view controls, home buttons, opacity controls, and legends.

Details

This function generates JavaScript that listens for overlayadd or baselayerchange events and automatically sets the view or zoom level according to the specified view_settings. If home_btns is enabled, a home button is added next to each layer in the layer control. When clicked, it zooms the map to the predefined view of that layer. The opacity control slider allows users to adjust the opacity of layers. The legend will be appended to the corresponding layer control, matched by the layer's group name.

Examples

library(sf)
library(leaflet)
library(leafem)

# Example data ##########
breweries91 <- st_as_sf(breweries91)
lines <- st_as_sf(atlStorms2005)
polys <- st_as_sf(leaflet::gadmCHE)

# View settings ##########
view_settings <- list(
  "Base_tiles1" = list(
    coords = c(20, 50),
    zoom = 3
  ),
  "Base_tiles2" = list(
    coords = c(-110, 50),
    zoom = 5
  ),
  "breweries91" = list(
    coords = as.numeric(st_coordinates(st_centroid(st_union(breweries91)))),
    zoom = 8
  ),
  "atlStorms2005" = list(
    coords = as.numeric(st_bbox(lines)),
    options = list(padding = c(110, 110))
  ),
  "gadmCHE" = list(
    coords = as.numeric(st_bbox(polys)),
    options = list(padding = c(2, 2)),
    fly = TRUE
  )
)

# Opacity control settings ##########
opacityControl <- list(
  "breweries91" = list(
    min = 0,
    max = 1,
    step = 0.1,
    default = 1,
    width = '100%',
    class = 'opacity-slider'
  )
)

# Legends ##########
legends <- list(
  "breweries91" = "<div>Legend for breweries</div>"
)

leaflet() %>%
  ## Baselayer
  addTiles(group = "Base_tiles1") %>%
  addProviderTiles("CartoDB", group = "Base_tiles2") %>%

  ## Overlays
  addCircleMarkers(data = breweries91, group = "breweries91") %>%
  addPolylines(data = lines, group = "atlStorms2005") %>%
  addPolygons(data = polys, group = "gadmCHE") %>%

  ## Extend Layers Control
  extendLayersControl(
    view_settings, home_btns = TRUE,
    home_btn_options = list(
      "Base_tiles1" = list(text = '🏡', cursor = 'ns-resize', class = 'homebtn'),
      "Base_tiles2" = list(text = '❤️', cursor = 'pointer'),
      "atlStorms2005" = list(text = '🌎', cursor = 'all-scroll'),
      "breweries91" = list(text = '🌎', styles = 'background-color: red'),
      "gadmCHE" = list(text = '🌎', styles = 'float: none;')
    ),
    opacityControl = opacityControl,
    includelegends = TRUE
  ) %>%

  ## LayersControl
  addLayersControl(
    baseGroups = c("Base_tiles1", "Base_tiles2"),
    overlayGroups = c("breweries91", "atlStorms2005", "gadmCHE"),
    options = layersControlOptions(collapsed = FALSE, autoZIndex = TRUE)
  )