addRasterImage
Add a raster image as a layer
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--seeraster
- colors
the color palette (see
colorNumeric
) or function to use to color the raster values (hint: if providing a function, setna.color
to"#00000000"
to makeNA
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 projectx
to the map projection expected by Leaflet (EPSG:3857
); ifFALSE
, it's the caller's responsibility to ensure thatx
is already projected, and thatextent(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 ifproject = FALSE
. SeeprojectRaster
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 toleaflet()
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
# NOT RUN {
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)
}
# }