R Shiny Leaflet 如何根据缩放级别更改圆圈大小

Question

我正在使用 Leaflet 地图创建一个闪亮的应用程序。它上面绘制了数千个小圆圈，圆圈的颜色讲述了一个故事。缩小时，圆圈保持较小（权重=1），因此它们重叠较少。然而，当用户放大时，小圆圈变得难以看到。我希望根据缩放级别增加圆圈的大小。我知道有一个input$MAPID_zoom 功能可以将缩放级别作为整数返回。

以下是一些可重现的代码，它将德克萨斯州达拉斯的 15 个随机点绘制到一张传单地图上，缩放设置为 6。当缩放级别增加到 8 时，我将如何将圆圈的权重从 1 更改为 2 , 放大到 10 时从 2 变为 3？

我在网上看到了一些讨论，但没有什么对我有用。请参阅下面的代码。提前致谢。

## app.R ##
library(leaflet)

ui <- dashboardPage(
  dashboardHeader(title = "Basic dashboard"),
  dashboardSidebar(),
  dashboardBody(
    leafletOutput("Map", width = "100%", height = "500px")
    
  )
)

server <- function(input, output) {

  df <- data.frame("Lat"=c(32.921821,32.910853,32.793803,32.995084,32.683745,32.759999,32.800652,32.958861,32.835963,32.762578,32.649651,32.862843,32.862217,32.936876,32.963381),
                   "Long"=c(-96.840609,-96.738831,-96.689232,-96.857858,-96.825345,-96.684475,-96.794144,-96.816111,-96.676371,-96.897331,-96.944426,-96.754719,-96.856976,-96.752718,-96.770249))

   output$Map <- renderLeaflet({
     leaflet(df) %>%
       addTiles(urlTemplate = "//{s}.tiles.mapbox.com/v3/jcheng.map-5ebohr46/{z}/{x}/{y}.png",
                attribution = 'Maps by <a href="http://www.mapbox.com/">Mapbox</a>') %>% 
       setView(lng = -96.84, lat = 32.92, zoom = 6) %>%
       addCircles(lng = ~Long, lat = ~Lat, weight = 1,
                        opacity = 1, fill = TRUE,  fillOpacity = 1 )
   })
}
shinyApp(ui, server)

Answer 1

好吧，这最终比我想象的更复杂，但我终于让它工作了。有一个观察者是关键。我还必须了解什么是 leafletProxy()（如果您不知道，请研究它）。最后，在观察者中使用 clearShapes() 清除形状是在放大和缩小时使其正常工作的关键。请参阅下面的代码。

## app.R ##
library(leaflet)
library(shinydashboard)
library(shinydashboardPlus)
library(dplyr)
ui <- dashboardPage(
  dashboardHeader(title = "Basic dashboard"),
  dashboardSidebar(),
  dashboardBody(
    leafletOutput("map", width = "100%", height = "500px")
    
  )
)

server <- function(input, output,session) {
  
  df <- data.frame("Lat"=c(32.921821,32.910853,32.793803,32.995084,32.683745,32.759999,32.800652,32.958861,32.835963,32.762578,32.649651,32.862843,32.862217,32.936876,32.963381),
                   "Long"=c(-96.840609,-96.738831,-96.689232,-96.857858,-96.825345,-96.684475,-96.794144,-96.816111,-96.676371,-96.897331,-96.944426,-96.754719,-96.856976,-96.752718,-96.770249))
  
  observeEvent(
    eventExpr = input$map_zoom, {
      print(input$map_zoom)           # Display zoom level in the console
      leafletProxy(
        mapId = "map", 
        session = session
      )%>% clearShapes() %>%
        addCircles(data=df,lng = ~Long, lat = ~Lat, 
                   weight = case_when(input$map_zoom <=4 ~1, 
                                      input$map_zoom ==5 ~2, 
                                      input$map_zoom ==6 ~3, 
                                      input$map_zoom ==7 ~5, 
                                      input$map_zoom ==8 ~7, 
                                      input$map_zoom ==9 ~9, 
                                      input$map_zoom >9 ~11),
                   opacity = 1, fill = TRUE, fillOpacity = 1 )
    }
  )
  
  output$map <- renderLeaflet({
    leaflet() %>%
      addTiles(urlTemplate = "//{s}.tiles.mapbox.com/v3/jcheng.map-5ebohr46/{z}/{x}/{y}.png",
               attribution = 'Maps by <a href="http://www.mapbox.com/">Mapbox</a>') %>%
      setView(lng = -96.84, lat = 32.92, zoom = 6) 
  })
}
shinyApp(ui, server)

Answer 2

试试这个

output$Map <- renderLeaflet({
    new_zoom <- 6
    wt <- 2
    if(!is.null(input$Map_zoom)) new_zoom <- input$Map_zoom
    
    leaflet(df) %>%
      addTiles(urlTemplate = "//{s}.tiles.mapbox.com/v3/jcheng.map-5ebohr46/{z}/{x}/{y}.png",
               attribution = 'Maps by <a href="http://www.mapbox.com/">Mapbox</a>') %>% 
      setView(lng = -96.84, lat = 32.92, zoom=new_zoom ) %>%
      addCircles(lng = ~Long, lat = ~Lat, weight = wt, # radius=radius,
                 opacity = 1, fill = TRUE,  fillOpacity = 1 )
  })