R object class representing a QGIS layer.

R object class representing a QGIS layer.

qgislayer(layerinfo)

Arguments

layerinfo	a list of layer members as parsed from a Network API JSON response

Value

A list of class qgislayer. Although the exact member fields might depend on the layer type, a qgislayer can be expected to contain at least the following fields:

id

QGIS-internal id string for the layer

crs

an rgdal::CRS object

extent

a numeric vector of class bbox (as would be returned by a call to sf::st_bbox()), giving the layer extents in coordinates of the projection (order xMin, yMin, xMax, yMax)

Details

A qgislayer is simply a list, containing all members as parsed from the Network API's JSON response.

While the parsed JSON response only contains string and numeric primitives, the qgislayer() constructor automatically parses some fields to appropriate R types.

Several functions that normally take a layer id (such as mapLayers.removeMapLayer()) also accept a qgislayer object for their id argument (see examples).

See also

mapLayer(), mapLayers(), mapCanvas.layers()

Examples

# make sure to use double braces to get the actual layer *element*, not its
# list position (which is a list of length 1 containing the layer element..)

layer <- iface.addTileLayer('http://c.tile.openstreetmap.org/{z}/{x}/{y}.png')
print(layer)
#> QGIS map layer with the following properties:
#> crs: CRS arguments:
#>  +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0
#> +k=1.0 +units=m +nadgrids=@null +no_defs 
#> valid: [1] TRUE
#> name: [1] "c.tile.openstreetmap.org tiles"
#> extent: [1] -20037508 -20037508  20037508  20037508
#> publicSource: [1] "type=xyz&url=http%3A%2F%2Fc.tile.openstreetmap.org%2F%7Bz%7D%2F%7Bx%7D%2F%7By%7D.png"
#> type: [1] 1
#> id: [1] "c_tile_openstreetmap_org_tiles20170830121005759"
#> isEditable: [1] FALSE

# identical results
mapLayers.removeMapLayer(layer)
#> [1] "c_tile_openstreetmap_org_tiles20170830121005759"
## mapLayers.removeMapLayer(layer$id)

# the qgislayer object is *not* synced up with QGIS -- while the object is still unchanged:
print(layer)
#> QGIS map layer with the following properties:
#> crs: CRS arguments:
#>  +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0
#> +k=1.0 +units=m +nadgrids=@null +no_defs 
#> valid: [1] TRUE
#> name: [1] "c.tile.openstreetmap.org tiles"
#> extent: [1] -20037508 -20037508  20037508  20037508
#> publicSource: [1] "type=xyz&url=http%3A%2F%2Fc.tile.openstreetmap.org%2F%7Bz%7D%2F%7Bx%7D%2F%7By%7D.png"
#> type: [1] 1
#> id: [1] "c_tile_openstreetmap_org_tiles20170830121005759"
#> isEditable: [1] FALSE

# re-retrieving the layer data from QGIS will fail:
mapLayer(layer$id)
#> Error in qgisremote("/qgis/mapLayer", c(id = checkqgislayer(id)), ...): 500: 'No layer with id: c_tile_openstreetmap_org_tiles20170830121005759'