在R Leaflet中以某些缩放级别显示图层 [英] Display layers at certain zoom levels in R Leaflet

问题描述

我正在使用R包"leaflet"制作交互式地图.

I am working on an interactive map with the R package "leaflet".

我想根据缩放级别自动更改可见层.

I would like to change automatically the visible layers depending on the zoom level.

例如，当放大时，我想让一个多边形层消失，取而代之的是一个点层.像这样的东西: https://tree-map.nycgovparks.org/

For example, I would like to have a polygon layer disappearing when zooming in, replaced by a points layer. Something like this : https://tree-map.nycgovparks.org/

我一直在尝试许多不同的技巧，并详细研究了"leaflet"和"leaflet.extras"软件包的帮助，但找不到任何解决方法.

I've been trying many different tricks and exploring in details the help from the "leaflet" and "leaflet.extras" packages, but could not find anything doing that.

我还从传单中直接找到了一些东西，但是在R下似乎无法复制:设置传单中各图层的缩放级别

I also found something straight from leaflet but it does not seem to be reproducible under R : Setting zoom level for layers in leaflet

我试图使用markerOptions中的minZoom和maxZoom选项，但它似乎并没有达到我想要的目的.

I tried to use the options minZoom and maxZoom from markerOptions, but it does not appear to do what I want.

这是此示例的代码:

require(spData)
require(leaflet)
require(sf)

# loading shapes of countries from the package spData

data(world)
world <- st_read(system.file("shapes/world.gpkg", package="spData"))

# creating a sf objet with oceanian countries boundaries

oceania <- world[world$continent=="Oceania",]

#loading points events from the quakes dataset

data(quakes)

#Creating a leaflet objet with points and polygons

leaflet() %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircleMarkers(lng=quakes$long,
                   lat=quakes$lat,
                   col="blue",
                   radius=3,
                   stroke=FALSE,
                   fillOpacity = 0.7,
                   options = markerOptions(minZoom=15, maxZoom=20)) %>%
  addPolygons(data= oceania,
              col="red")

它为我提供了来自openstreetmap的具有预期背景的预期图层，但是minZoom和maxZoom参数没有任何改变.我希望点图层仅出现在15到20的缩放级别之间，但似乎无法像这样工作.

It gives me the expected layers with the expected background from openstreetmap, but the minZoom and maxZoom arguments don't change anything. I expected the points layer to only appear between zoom levels 15 and 20, but it does not work like this, it seems.

来自查看器的图像

推荐答案

大多数"addElement()"类型函数中的 group 参数对于管理地图的工作方式非常重要.我推荐这样做，通过仔细考虑如何对数据进行分组，您可以做很多整洁的事情.

The group argument in most of the "addElement()" type functions becomes very important for managing how a map works. I recommend it, and you can do a lot of neat stuff by carefully thinking about how you group your data.

通过调用 groupOptions()，您可以为所需的任何图层设置缩放级别.在下面，我添加了您指定的缩放级别，但可以随意调整它以适应您的需求.

By calling groupOptions(), you can set the zoom levels for whatever layers you like. Below I have added the zoom levels you specified, but feel free to play around with it to adjust it to your needs.

#Creating a leaflet object with points and polygons

leaflet() %>%
  addProviderTiles(providers$CartoDB.Positron) %>%
  addCircleMarkers(lng=quakes$long,
                   lat=quakes$lat,
                   col="blue",
                   radius=3,
                   stroke=FALSE,
                   fillOpacity = 0.7,
                   #options = markerOptions(minZoom=15, maxZoom=20), # Oldcode
                   group = "Quake Points") %>%                       # Newcode
  addPolygons(data= oceania,
              col="red") %>%                        
  groupOptions("Quake Points", zoomLevels = 15:20)                   # Newcode

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