如何在Plotly R的scattermapbox类型地图中创建虚线

问题原因 #

Plotly的scattermapbox类型的line参数目前不支持dash或linetype属性，直接设置这两个参数不会生效。

有效解决方案：使用Mapbox图层绘制虚线 #

通过layout中的mapbox$layers添加自定义线图层，Mapbox线图层支持dasharray参数定义虚线样式，适配所有缩放级别，不会出现标记随缩放变形的问题。

修改后的代码 #

plot_ly() %>%
  layout(
    mapbox = list(
      style = "carto-positron",
      zoom = 6, 
      center = list(lon=21, lat=43),
      # 添加自定义虚线图层
      layers = list(
        list(
          type = "line",
          source = list(
            type = "FeatureCollection",
            features = list(
              list(
                type = "Feature",
                geometry = list(
                  type = "LineString",
                  coordinates = list(
                    # 坐标顺序为[经度, 纬度]，注意与scattermapbox的顺序相反
                    c(21.5869,42.2628), c(21.5625,42.343), c(21.7783,42.6513),
                    c(21.7534,42.7009), c(21.66,42.6828), c(21.5717,42.7294),
                    c(21.5717,42.7294), c(21.4095,42.7487), c(21.4351,42.8723),
                    c(21.2683,42.9085), c(21.228,43.0056), c(21.1695,43.0165),
                    c(21.1177,43.1198), c(20.9236,43.1461), c(20.8197,43.2725),
                    c(20.6184,43.1926), c(20.6824,43.1165), c(20.6589,43.0287),
                    c(20.506,42.9562), c(20.5121,42.8871), c(20.3529,42.8334),
                    c(20.3529,42.8334)
                  )
                )
              )
            )
          ),
          paint = list(
            "line-color" = "red",
            "line-width" = 1,
            # 定义虚线样式：[实线段长度, 空白段长度]，可调整数值改变虚实比例
            "line-dasharray" = c(2, 2)
          )
        )
      )
    )
  )

关键说明 #

• Mapbox图层坐标顺序为**[经度, 纬度]**，与scattermapbox的[纬度, 经度]顺序相反，需注意转换
• line-dasharray参数控制虚线样式，比如c(2,2)代表2个单位实线、2个单位空白，可根据需求调整数值
• 该方式绘制的虚线不会随地图缩放变形，完全符合要求的展示效果

内容的提问来源于stack exchange，提问作者stallingOne