R: Using addResourcePath for rendering local leaflet tiles - r

Question

I would like to add local tiles for leaflet to render them offline in a shiny application.
Although there are solutions to this on SO for example here and here , I am still ending up with grey map with no tiles. It would really help me to see some reproducible example.
Thanks.
My example code:
library(shiny)
library(dplyr)
library(RgoogleMaps)
#downloads tiles for a given regions, saves it to C:/Users/.../mapTiles/OSM
for (zoom in 0:16)
GetMapTiles(center = c(lat = 52.431635, lon = 13.194773),
zoom = zoom,
nTiles = round(c(20,20)/(17-zoom)))
#shiny ui
ui = fluidPage(leafletOutput("map"))
#create basic map, load tiles from directory and set view to centre of downloaded tiles
server = function(input, output, server){
addResourcePath(prefix = "OSM", "C:/Users/.../mapTiles")
output$map = renderLeaflet({
leaflet() %>%
addTiles( urlTemplate = "/OSM/{z}_{x}_{y}.png") %>%
setView(52.431635, 13.194773 , zoom = 10) %>% #set to the location with tiles
addMarkers(52.431635, 13.194773 )
}
)
}
shinyApp(ui, server)

Answer 1

In my case, I create my own tiles via gdal2tiles, which takes your data and automatically creates a {z}/{x}/{y}.png folder structure. Please see this link for a nice tutorial and what i mean about the file structure;
+---14
| +---8185
| +---5460.png
| +---5461.png
| +---etc.png
| \---8186
# I use the following server (see how my addTiles has a folder structure)
server <- function(input, output,session) {
addResourcePath("mytiles", "C:/.../tiles")
output$tilemap <- renderLeaflet({
leaflet() %>%
setView(lng = -4.4, lat = 52, zoom = 12) %>%
addTiles(urlTemplate = "mytiles/{z}/{x}/{y}.png")
})
}
Now, as you are downloading tiles from Google Maps to your hard drive, you'll want a slightly different approach as the files are downloaded in a {z}_{x}_{y}.png format, and not produced into a file structure like gdal creates;
+---11_1098_671.png
etc.
so you need to adjust your addTiles code to reflect this, using underscores, like the Google filenames;
server <- function(input, output,session) {
addResourcePath("mytiles", "C:/.../OSM")
output$tilemap <- renderLeaflet({
leaflet() %>%
setView(lng = 13.194773, lat = 52.431635, zoom = 11) %>%
addTiles(urlTemplate = "mytiles/{z}_{x}_{y}.png")
})
}
Lastly, my setView arguments are in a different order to yours but i'm not sure whether that makes a difference or not.

Answer 2

i tried this solution but it could not work,the topic is old but it really helped me to achieve what i wanted to do, i found another solution for those of you in the same case by creating two ports :
just define two differents ports for your shiny server( 3838) and for the server hosting the tiles (8000)
servr::httd(dir="C:/TestApp/data_hydrepat/tiles_hydrepat/mapTiles/mytiles",daemon=TRUE,port=8000)
options(shiny.port = 3838)
to close the server hosting the tiles, just put a reactive on an input or something.. and close
(servr::daemon_stop(which = daemon_list())
hope it'll help !