mapview::mapshot output png file image does not match the leaflet image in app.R

[ptepa]

# app.R - How to save a leaflet map as a png with the correct view?
# To run:
# R -e "shiny::runApp('../map', launch.browser = TRUE)"
# Click Save Map Image button and wait until the printed message 'Done'.
# Mac: open map.png
# Windows: start map.png
# Check that the map.png image matches that displayed in this app.
# The file unmatched.png shows that the map image displayed does not match the
# map image in the saved map.png file.
# For example the saved map.png file appears zoomed-out more and shows Boston
# whereas the map displayed in the app does not show that extended view.
# MacOS 10.13.6, R 4.2.1, shiny 1.7.4, leaflet 2.1.1, mapview 2.11.0,
# webshot 0.5.4
# Darwin.zip contains subdirectory Darwin.x86_64/bin/pandoc,phantomjs
# Windows.zip contains subdirectoryWindows/bin/pandoc.exe,phantomjs.exe

repository <- "http://cran.us.r-project.org"

if (!require(shiny)) install.packages("shiny", repos = repository)
if (!require(leaflet)) install.packages("leaflet", repos = repository)
if (!require(mapview)) install.packages("mapview", repos = repository)
if (!require(webshot)) install.packages("webshot", repos = repository)

the_map_width = "496px"
the_map_height = "372px"
#the_map_width = "512px"
#the_map_height = "512px"

ui <- fluidPage(
  leafletOutput(outputId = "map",
                width = the_map_width,
                height = the_map_height),
  actionButton(inputId = "save_map_image", label = "Save Map Image")
)

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

  # Add platform-specific bin sub-directory to PATH for pandoc and phantomjs
  # programs that are apparently called by mapview::mapshot(). UGLY.

  augment_path <- function() {
    current_path <- Sys.getenv("PATH")
    current_directory <- getwd()
    platform <- Sys.info()[["sysname"]]

    if (platform != "Windows") {
      platform <- paste0(platform, ".", Sys.info()[["machine"]])
    }

    new_path <- NULL

    if (platform == "Windows") {
      new_path <- paste0(current_path, ";", current_directory, "\\Windows\\bin")
    } else {
      new_path <-
        paste0(current_path, ":", current_directory, "/", platform, "/bin")

      # Also ensure the executables are executable:

      chmod_command <- paste0("chmod -R +x ", platform)
      system(chmod_command)
    }

    Sys.setenv(PATH = new_path)
  }

  augment_path()
  print(Sys.getenv("PATH"))

  create_map <- function() {
    # Starting view is New York:
    west <- -74.36371
    east <- -71.6391
    south <- 40.68272
    north <- 42.21428
    result <- leaflet() %>%
      addTiles(options = list(minZoom = 2)) %>%
      fitBounds(west, south, east, north) %>%
      setMaxBounds(-180.0, -90.0, 180.0, 90.0) %>%
      addScaleBar(position = "topleft", options = list(imperial = FALSE))
    return(result)
  }

  the_map <- create_map()
  output$map <- renderLeaflet(the_map)

  observeEvent(input$save_map_image, {
    # How to get the_map current bounds and zoom level and pass it to mapshot()?
    cat("the_map = "); str(the_map)
    cat("input$map = "); str(input$map)
    cat("input$map_bounds = "); str(input$map_bounds) # This works.
    cat("input$map_zoom = "); str(input$map_zoom)
    cat("input$map_center$lng = "); str(input$map_center$lng)
    cat("input$map_center$lat = "); str(input$map_center$lat)
    the_map_zoom <- input$map_zoom
    file_name <- paste0(getwd(), "/map.png")
    #mapview::mapshot(the_map, file = file_name,
    #                 vwidth = the_map_width, vheight = the_map_height)
    # https://github.com/r-spatial/mapview/issues/414
    mapview::mapshot(the_map %>%
                     setView(lng = input$map_center$lng,
                             lat = input$map_center$lat,
                             zoom = input$map_zoom),
                     file = file_name,
                     vwidth = the_map_width,
                     #vheight = the_map_height,
                     wheight = the_map_height,
                     expand = 0, cliprect = "viewport", selfcontained = FALSE)
    cat("Done writing ", file_name, "\n")
  })

  # Callback for map pan/zoom events.
  # Check and adjust map bounds to stay within 'non-replicated view'
  # (that does not cross the +/-180 line):

  observeEvent(input$map_bounds, {
    bounds_list <- input$map_bounds
    west <- bounds_list$west
    east <- bounds_list$east
    south <- bounds_list$south
    north <- bounds_list$north

    if (west == east) east <- west + 1.0
    if (south == north) north <- south + 1.0

    if (west <= -180.0) west <- -179.0
    if (east >= 180.0) east <- 179.0
    if (south <= -90.0) south <- -89.0
    if (north >= 90.0) north <- 89.0

    the_map <<- fitBounds(the_map, west, south, east, north)
    cat("input$map_center$lng = "); str(input$map_center$lng)
    cat("input$map_center$lat = "); str(input$map_center$lat)
    cat("input$map_bounds = "); str(input$map_bounds) # This works.
    cat("input$map_zoom = "); str(input$map_zoom)
  })

}

shinyApp(ui, server)

Darwin.zip Windows.zip