How to save a leaflet map in Shiny

Question

Following on from this question, I am looking to save and download a leaflet map as a png or jpeg image. I have the following code but I keep getting an error.

ui <- fluidPage(
  leafletOutput("map"),
  downloadButton("dl")
)

server <- function(input, output, session) {
  output$map <- renderLeaflet({
    leaflet() %>% 
      addTiles()
  })

  output$dl <- downloadHandler(
    filename = "map.png",

    content = function(file) {
      mapshot(input[["map"]], file = file)
    }
  )
}

shinyApp(ui = ui, server = server)

The error I get when I try to download (by clicking the button) is

Warning: Error in system.file: 'package' must be of length 1
Stack trace (innermost first):
    65: system.file
    64: readLines
    63: paste
    62: yaml.load
    61: yaml::yaml.load_file
    60: getDependency
    59: widget_dependencies
    58: htmltools::attachDependencies
    57: toHTML
    56: <Anonymous>
    55: do.call
    54: mapshot
    53: download$func [#11]
     4: <Anonymous>
     3: do.call
     2: print.shiny.appobj
     1: <Promise>
Error : 'package' must be of length 1

Bonus points if you can tell me how to get this working with leafletProxy.

Answer 1

May be this would help:

  server <- function(input, output, session) {

    map <- reactiveValues(dat = 0)

      output$map <- renderLeaflet({
        map$dat <- leaflet() %>% 
          addTiles()
      })

      output$dl <- downloadHandler(
        filename = "map.png",

        content = function(file) {
          mapshot(map$dat, file = file)
        }
      )
    }

Answer 2

Overview

Since 'leaflet' maps are interactive, the leaflet object being used in mapview::mapshot() function must be interactive. Accounting for this allows for the user to save their version of a leaflet map within the Shiny app.

# install necessary packages
install.packages( c( "shiny", "leaflet", "mapview" ) )

# load necessary packages
library( shiny )
library( leaflet )
library( mapview )

ui <- fluidPage(
  leafletOutput( outputId = "map"),
  downloadButton( outputId = "dl")
)

server <- function(input, output, session) {

  # Create foundational leaflet map
  # and store it as a reactive expression
  foundational.map <- reactive({

    leaflet() %>% # create a leaflet map widget

      addTiles( urlTemplate = "https://{s}.tile.openstreetmap.se/hydda/base/{z}/{x}/{y}.png" ) # specify provider tile and type

  }) # end of foundational.map()

  # render foundational leaflet map
  output$map <- leaflet::renderLeaflet({

    # call reactive map
    foundational.map()

  }) # end of render leaflet

  # store the current user-created version
  # of the Leaflet map for download in 
  # a reactive expression
  user.created.map <- reactive({

    # call the foundational Leaflet map
    foundational.map() %>%

      # store the view based on UI
      setView( lng = input$map_center$lng
               ,  lat = input$map_center$lat
               , zoom = input$map_zoom
      )

  }) # end of creating user.created.map()



  # create the output file name
  # and specify how the download button will take
  # a screenshot - using the mapview::mapshot() function
  # and save as a PDF
  output$dl <- downloadHandler(
    filename = paste0( Sys.Date()
                       , "_customLeafletmap"
                       , ".pdf"
    )

    , content = function(file) {
      mapshot( x = user.created.map()
               , file = file
               , cliprect = "viewport" # the clipping rectangle matches the height & width from the viewing port
               , selfcontained = FALSE # when this was not specified, the function for produced a PDF of two pages: one of the leaflet map, the other a blank page.
      )
    } # end of content() function
  ) # end of downloadHandler() function

} # end of server

# run the Shiny app
shinyApp(ui = ui, server = server)

# end of script #

Final result

Once you run the Shiny app, open the app in a new window.

Once in the browser, go ahead and click Download. It took about ~3 seconds.

Once Download has been clicked, you'll promptly see a PDF file wherever your downloaded files are stored on your machine.

References

My ideas sprung from the following posts:

• Save leaflet map in Shiny

• How to save a leaflet map in Shiny

• Input/Events - Leaflet for R

• Thanks to @blondeclover, there is no need to store the bounds of the leaflet map when using setView(). Instead, simply use input$MAPID_center$lng and input$MAPID_center$lat when using setView().

  • To learn more about other leaflet inputs, please see list input handlers for a package shiny leaflet.