Map {rgee}

R6 object (Map) to display Earth Engine (EE) spatial objects

Description

Create interactive visualizations of spatial EE objects (ee$FeatureCollection, ee$ImageCollection, ee$Geometry, ee$Feature, and ee$Image.) using leaflet in the backend.

Usage

Map

Format

An object of class environment with the following functions:

• addLayer(eeObject, visParams, name = NULL, shown = TRUE, opacity = 1, titiler_viz_convert = TRUE, titiler_server = "https://api.cogeo.xyz/"): Adds a given EE object to the map as a layer.
  

  • eeObject: The object to add to the interactive map.
    

  • visParams: List of parameters for visualization. See details.
    

  • name: The name of the layer.
    

  • shown: A flag indicating whether the layer should be on by default.
    

  • opacity: The layer's opacity is represented as a number between 0 and 1. Defaults to 1.
    

  • titiler_viz_convert: Logical. If it is TRUE, Map$addLayer will transform the visParams to titiler style. Ignored if eeObject is not a COG file.
    

  • titiler_server: TiTiler endpoint. Defaults to "https://api.cogeo.xyz/".

• addLayers(eeObject, visParams, name = NULL, shown = TRUE, opacity = 1): Adds a given ee$ImageCollection to the map as multiple layers.
  

  • eeObject: The ee$ImageCollection to add to the interactive map.
    

  • visParams: List of parameters for visualization. See details.
    

  • name: The name of layers.
    

  • shown: A flag indicating whether layers should be on by default.
    

  • opacity: The layer's opacity is represented as a number between 0 and 1. Defaults to 1.
    

  • nmax: Numeric. The maximum number of images to display. By default 5.

• addLegend(visParams, name = "Legend", position = c("bottomright", "topright", "bottomleft", "topleft"), color_mapping= "numeric", opacity = 1, ...): Adds a given ee$ImageCollection to the map as multiple layers.
  

  • visParams: List of parameters for visualization.
    

  • name: The title of the legend.
    

  • position: Character. The position of the legend. By default bottomright.
    

  • color_mapping: Map data values (numeric or factor/character) to colors according to a given palette. Use "numeric" ("discrete") for continuous (categorical) data. For display characters use "character" and add to visParams the element "values" containing the desired character names.
    

  • opacity: The legend's opacity is represented as a number between 0 and 1. Defaults to 1.
    

  • ...: Extra legend creator arguments. See addLegend.
    

• setCenter(lon = 0, lat = 0, zoom = NULL): Centers the map view at the given coordinates with the given zoom level. If no zoom level is provided, it uses 1 by default.

  • lon: The longitude of the center, in degrees.
    

  • lat: The latitude of the center, in degrees.
    

  • zoom: The zoom level, from 1 to 24.

• setZoom(zoom = NULL): Sets the zoom level of the map.

  • zoom: The zoom level, from 1 to 24.

• centerObject(eeObject, zoom = NULL, maxError = ee$ErrorMargin(1)): Centers the map view on a given object. If no zoom level is provided, it will be predicted according to the bounds of the Earth Engine object specified.

  • eeObject: EE object.
    

  • zoom: The zoom level, from 1 to 24.

  • maxError: Max error when input image must be reprojected to an explicitly requested result projection or geodesic state.

Details

Map use the Earth Engine method getMapId to fetch and return an ID dictionary being used to create layers in a leaflet object. Users can specify visualization parameters to Map$addLayer by using the visParams argument. Each Earth Engine spatial object has a specific format. For ee$Image, the parameters available are:

Parameter	Description	Type
bands	Comma-delimited list of three band (RGB)	list
min	Value(s) to map to 0	number or list of three numbers, one for each band
max	Value(s) to map to 1	number or list of three numbers, one for each band
gain	Value(s) by which to multiply each pixel value	number or list of three numbers, one for each band
bias	Value(s) to add to each Digital Number value	number or list of three numbers, one for each band
gamma	Gamma correction factor(s)	number or list of three numbers, one for each band
palette	List of CSS-style color strings (single-band only)	comma-separated list of hex strings
opacity	The opacity of the layer (from 0 to 1)	number

If you add an ee$Image to Map$addLayer without any additional parameters, by default it assigns the first three bands to red, green, and blue bands, respectively. The default stretch is based on the min-max range. On the other hand, the available parameters for ee$Geometry, ee$Feature, and ee$FeatureCollection are:

• color: A hex string in the format RRGGBB specifying the color to use for drawing the features. By default #000000.

• pointRadius: The radius of the point markers. By default 3.

• strokeWidth: The width of lines and polygon borders. By default 3.

Value

Object of class leaflet, with the following extra parameters: tokens, name, opacity, shown, min, max, palette, and legend. Use the $ method to retrieve the data (e.g. m$rgee$min).

Examples

## Not run: 
library(rgee)
library(sf)

ee_Initialize()

# Case 1: Geometry*
geom1 <- ee$Geometry$Point(list(-73.53, -15.75))
Map$centerObject(geom1, zoom = 8)
m1 <- Map$addLayer(
  eeObject = geom1,
  visParams = list(
    pointRadius = 10,
    color = "FF0000"
  ),
  name = "Geometry-Arequipa"
)

# Case 2: Feature
feature_arq <- ee$Feature(ee$Geometry$Point(list(-72.53, -15.75)))
m2 <- Map$addLayer(
  eeObject = feature_arq,
  name = "Feature-Arequipa"
)
m2 + m1

# Case 4: Image
image <- ee$Image("LANDSAT/LC08/C01/T1/LC08_044034_20140318")
Map$centerObject(image)
m4 <- Map$addLayer(
  eeObject = image,
  visParams = list(
    bands = c("B4", "B3", "B2"),
    max = 10000
  ),
  name = "SF"
)

# Case 5: ImageCollection
nc <- st_read(system.file("shape/nc.shp", package = "sf")) %>%
  st_transform(4326) %>%
  sf_as_ee()

ee_s2 <- ee$ImageCollection("COPERNICUS/S2")$
  filterDate("2016-01-01", "2016-01-31")$
  filterBounds(nc)
ee_s2 <- ee$ImageCollection(ee_s2$toList(2))

Map$centerObject(nc$geometry())
m5 <- Map$addLayers(ee_s2)
m5

# Case 6: Map comparison
image <- ee$Image("LANDSAT/LC08/C01/T1/LC08_044034_20140318")
Map$centerObject(image)
m_ndvi <- Map$addLayer(
  eeObject = image$normalizedDifference(list("B5", "B4")),
  visParams = list(min = 0, max = 0.7),
  name = "SF_NDVI"
) + Map$addLegend(list(min = 0, max = 0.7), name = "NDVI", position = "bottomright", bins = 4)
m6 <- m4 | m_ndvi
m6

# Case 7: digging up the metadata
m6$rgee$tokens
m5$rgee$tokens

# Case 8: COG support
# See parameters here: https://api.cogeo.xyz/docs

server <- "https://storage.googleapis.com/pdd-stac/disasters/"
file <- "hurricane-harvey/0831/20170831_172754_101c_3B_AnalyticMS.tif"
resource <- paste0(server, file)
visParams <- list(bands = c("B3", "B2", "B1"), min = 3000, max = 13500, nodata = 0)
Map$centerObject(resource)
Map$addLayer(resource, visParams = visParams, shown = TRUE)

## End(Not run)