mapgl-draw-then-save.R

library(shiny)
library(bslib)
library(mapgl)
library(sf)

ui <- page_fluid(
  theme = bs_theme(version = 5, bootswatch = "flatly"),
  
  h2("mapgl Drawing Demo"),
  
  layout_sidebar(
    sidebar = sidebar(
      width = 300,
      downloadButton("download_features", "Download GeoJSON", class = "btn-success")
    ),
    
    layout_column_wrap(
      width = 1/2,
      mapboxglOutput("map", height = "600px"),
      verbatimTextOutput("feature_info")
    )
  )
)

server <- function(input, output, session) {
  
  output$map <- renderMapboxgl({
    mapboxgl(
      center = c(13.4050, 52.5200),  # Longitude and latitude for Berlin
      zoom = 10
    ) %>%
      add_draw_control()
  })
  
  output$feature_info <- renderPrint({
    features <- get_drawn_features(mapboxgl_proxy("map"))
    if (!is.null(features) && nrow(features) > 0) {
      print(features)
    } else {
      "No features drawn yet."
    }
  })
  
  output$download_features <- downloadHandler(
    filename = function() {
      "drawn_features.geojson"
    },
    content = function(file) {
      features <- get_drawn_features(mapboxgl_proxy("map"))
      if (!is.null(features) && nrow(features) > 0) {
        st_write(features, file, driver = "GeoJSON")
      } else {
        file.create(file)  # Create an empty file if no features are drawn
      }
    }
  )
}

shinyApp(ui, server)