leaflet: addRasterImage – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

addRasterImage

Add a raster image as a layer

Description

Create an image overlay from a RasterLayer object. This is only suitable for small to medium sized rasters, as the entire image will be embedded into the HTML page (or passed over the websocket in a Shiny context).

Usage

addRasterImage(
  map,
  x,
  colors = if (raster::is.factor(x)) "Set1" else "Spectral",
  opacity = 1,
  attribution = NULL,
  layerId = NULL,
  group = NULL,
  project = TRUE,
  method = c("auto", "bilinear", "ngb"),
  maxBytes = 4 * 1024 * 1024,
  data = getMapData(map)
)

projectRasterForLeaflet(x, method)

Arguments

`map`	a map widget object
`x`	a `RasterLayer` object–see `raster`
`colors`	the color palette (see `colorNumeric`) or function to use to color the raster values (hint: if providing a function, set `na.color` to `"#00000000"` to make `NA` areas transparent)
`opacity`	the base opacity of the raster, expressed from 0 to 1
`attribution`	the HTML string to show as the attribution for this layer
`layerId`	the layer id
`group`	the name of the group this raster image should belong to (see the same parameter under `addTiles`)
`project`	if `TRUE`, automatically project `x` to the map projection expected by Leaflet (`EPSG:3857`); if `FALSE`, it's the caller's responsibility to ensure that `x` is already projected, and that `extent(x)` is expressed in WGS84 latitude/longitude coordinates
`method`	the method used for computing values of the new, projected raster image. `"bilinear"` (the default) is appropriate for continuous data, `"ngb"` - nearest neighbor - is appropriate for categorical data. Ignored if `project = FALSE`. See `projectRaster` for details.
`maxBytes`	the maximum number of bytes to allow for the projected image (before base64 encoding); defaults to 4MB.
`data`	the data object from which the argument values are derived; by default, it is the `data` object provided to `leaflet()` initially, but can be overridden

Details

The maxBytes parameter serves to prevent you from accidentally embedding an excessively large amount of data into your htmlwidget. This value is compared to the size of the final compressed image (after the raster has been projected, colored, and PNG encoded, but before base64 encoding is applied). Set maxBytes to Inf to disable this check, but be aware that very large rasters may not only make your map a large download but also may cause the browser to become slow or unresponsive.

By default, the addRasterImage function will project the RasterLayer x to EPSG:3857 using the raster package's projectRaster function. This can be a time-consuming operation for even moderately sized rasters. Upgrading the raster package to 2.4 or later will provide a large speedup versus previous versions. If you are repeatedly adding a particular raster to your Leaflet maps, you can perform the projection ahead of time using projectRasterForLeaflet(), and call addRasterImage with project = FALSE.

Examples

library(raster)

r <- raster(xmn = -2.8, xmx = -2.79, ymn = 54.04, ymx = 54.05, nrows = 30, ncols = 30)
values(r) <- matrix(1:900, nrow(r), ncol(r), byrow = TRUE)
crs(r) <- CRS("+init=epsg:4326")

if (requireNamespace("rgdal")) {
  leaflet() %>% addTiles() %>%
    addRasterImage(r, colors = "Spectral", opacity = 0.8)
}

leaflet

Create Interactive Web Maps with the JavaScript 'Leaflet' Library

v2.0.4.1

GPL-3

Authors

Joe Cheng [aut, cre], Bhaskar Karambelkar [aut], Yihui Xie [aut], Hadley Wickham [ctb], Kenton Russell [ctb], Kent Johnson [ctb], Barret Schloerke [ctb], jQuery Foundation and contributors [ctb, cph] (jQuery library), Vladimir Agafonkin [ctb, cph] (Leaflet library), CloudMade [cph] (Leaflet library), Leaflet contributors [ctb] (Leaflet library), Brandon Copeland [ctb, cph] (leaflet-measure plugin), Joerg Dietrich [ctb, cph] (Leaflet.Terminator plugin), Benjamin Becquet [ctb, cph] (Leaflet.MagnifyingGlass plugin), Norkart AS [ctb, cph] (Leaflet.MiniMap plugin), L. Voogdt [ctb, cph] (Leaflet.awesome-markers plugin), Daniel Montague [ctb, cph] (Leaflet.EasyButton plugin), Kartena AB [ctb, cph] (Proj4Leaflet plugin), Robert Kajic [ctb, cph] (leaflet-locationfilter plugin), Mapbox [ctb, cph] (leaflet-omnivore plugin), Michael Bostock [ctb, cph] (topojson), RStudio [cph]

Initial release