用矢量增强R中的线性图像分辨率

Question

我正在使用谷歌在城市列表上迭代ggmap请求。使用styles参数，我删除除道路之外的所有元素。

请参阅下面的1280x1280图像输出。

图像的分辨率有限制（1280 x 1280），但我想以更高的分辨率（最好是4k x 4k）打印出城市。

鉴于图像实际上只是线条，是否有一种方法可以使用一组方向向量增强R中的锐度？

style <- c(c(feature = "administrative", visibility = "off"),
       c("&style=", feature = "all", element = "labels", visibility = "off"),
       c("&style=", feature = "road", color = "black"),
       c("&style=", feature = "landscape", color = "0xffffff"),
       c("&style=", feature = "water", color = "0xffffff"),
       c("&style=", feature = "poi", color = "0xffffff"),
       c("&style=", feature = "transit", color = "0xffffff"),
       c("&style=", feature = "transit.line", weight = "0"),
       c("&style=", feature = "transit.line", color = "black")
      )

ggmap(get_googlemap(center = "Chengdu", 
  zoom = 10, 
  source = "google", 
  maptype = "roadmap",
  #color = "bw",
  size = c(640, 640),
  format = "png8",
  messaging = FALSE,
  scale = 2,
  style = style),
  extent = "device")