How to style rasters added to a leaflet map with addTileFolder?

[jpd-defra]

Hello,

I've created a set of tiles with gdal2tiles.py I can get them to display on the leaflet map with addTileFolder, but from the docs can't work out how to style the raster(s). Which options can I use to provide a colour palette?

My code looks like this:

leaflet() %>%
  addTiles() %>%
  addTileFolder(
    "/tmp/30by30_tiles_WGS84",
    tms = TRUE,
    layerId = NULL,
    group = NULL,
    attribution = NULL,
    options = leaflet::tileOptions(),
    data = leaflet::getMapData(.)
  )

And my map looks like this - the raster extent is correct.

If there's a bit more detail to add to the docs, I would be happy to do this in a PR.

Any help much appreciated!

[tim-salabim]

Hi, its a long time since i have looked into addTileFolder. Any chance you can supply the data?

[jpd-defra]

Hi @tim-salabim , I can't share my actual data, so I've created some dummy data to illustrate the problem with the following code:

library(raster)
set.seed(42) 

xmin <- 400000  
xmax <- 600000
ymin <- 0
ymax <- 300000 
resolution <- 500

r <- raster(xmn = xmin, xmx = xmax, ymn = ymin, ymx = ymax, 
            resolution = resolution, crs = CRS("+init=epsg:27700"))
values(r) <- sample(c(0, 1), ncell(r), replace = TRUE)
r_reprojected <- projectRaster(r, crs = CRS("+init=epsg:4326"), method = "ngb")
writeRaster(r_reprojected, "/tmp/binary_raster_epsg4326.tif", format = "GTiff", overwrite = TRUE)

Then I fed this into gdal and used:

gdal_translate -of VRT -ot Byte -scale /tmp/binary_raster_epsg4326.tif temp.vrt
gdal2tiles.py --zoom=3-10 --processes=8 temp.vrt /tmp/dummy_tiles_WGS84

And the tiled data is here.

I then add this dummy data to the map with:

leaflet() %>%
  addTiles() %>%
  setView(-0.91431, 51.59701, zoom = 7) %>%
  addTileFolder(
    "/tmp/dummy_tiles_WGS84",
    tms = TRUE,
    layerId = NULL,
    group = NULL,
    attribution = NULL,
    options = leaflet::tileOptions(),
    data = leaflet::getMapData(.)
)

And the map looks like this:

So it is styling a bit differently to my previous image, but my question still remains around how to change this styling.

[tim-salabim]

Thanks, I'll have a look