Add a flatgeobuf file to leaflet map

flatgeobuf is a performant binary geo-spatial file format suitable for serving large data. For more details see https://github.com/flatgeobuf/flatgeobuf and the respective documentation for the GDAL/OGR driver at https://gdal.org/en/latest/drivers/vector/flatgeobuf.html.

In contrast to classical ways of serving data from R onto a leaflet map, flatgeobuf can stream the data chunk by chunk so that rendering of the map is more or less instantaneous. The map is responsive while data is still loading so that popup queries, zooming and panning will work even though not all data has been rendered yet. This makes for a rather pleasant user experience as we don't have to wait for all data to be added to the map before interacting with it.

Usage

addFgb(
  map,
  file = NULL,
  url = NULL,
  layerId = NULL,
  group = NULL,
  popup = NULL,
  label = NULL,
  radius = 10,
  stroke = TRUE,
  color = "#03F",
  weight = 5,
  opacity = 0.5,
  fill = FALSE,
  fillColor = NULL,
  fillOpacity = 0.2,
  dashArray = NULL,
  options = NULL,
  className = NULL,
  scale = scaleOptions(),
  minZoom = NULL,
  maxZoom = 52,
  highlightOptions = NULL,
  labelOptions = NULL,
  ...
)

Arguments

map: a mapview or leaflet object.
file: file path to the .fgb file to be added to map. If set, url is ignored.
url: url of the data to be added to map. Only respected if file = NULL.
layerId: the layer id.
group: the group name for the file to be added to map.
popup: either a logical of whether to show the feature properties (fields) in popups or the name of the field to show in popups.
label: name of the field to be shown as a tooltip.
radius: the size of the circle markers.
stroke: whether to draw stroke along the path (e.g. the borders of polygons or circles).
color: stroke color.
weight: stroke width in pixels.
opacity: stroke opacity.
fill: whether to fill the path with fillColor. If fillColor is set, this will be set to TRUE, default is FALSE.
fillColor: fill color. If set, fill will be set to TRUE.
fillOpacity: fill opacity.
dashArray: a string that defines the stroke dash pattern.
options: a list of extra options for tile layers, popups, paths (circles, rectangles, polygons, ...), or other map elements.
className: optional class name for the popup (table). Can be used to define css for the popup.
scale: named list with instructions on how to scale radius, width, opacity, fillOpacity if those are to be mapped to an attribute column.
minZoom: minimum zoom level at which data should be rendered.
maxZoom: maximum zoom level at which data should be rendered.
highlightOptions: Options for highlighting the shape on mouse over.
labelOptions: A Vector of labelOptions to provide label options for each label. Default NULL
...: currently not used.

Details

Styling options in addFgb offer flexibility by allowing users to either specify styles directly as function arguments or define them as attributes in the data object:

Direct Styling: You can pass style arguments (e.g., color, weight, opacity) directly to the function. These will apply uniformly to all features in the layer.

Attribute-based Styling: Alternatively, you can include styling properties (e.g., color, fillColor, weight) as columns in your data object before writing it to an FGB file. Set the corresponding arguments in addFgb to NULL, and the function will use these attributes for styling during map rendering.

For example:

## using custom `color`
data$color <- colorNumeric(palette = "viridis", domain = data$var)(data$var)
sf::st_write(obj = data, dsn = "myfile.fgb", driver = "FlatGeobuf")
leafem::addFgb(file = "myfile.fgb", color = NULL)

## using custom `fillColor`
data$fillColor <- colorNumeric(palette = "viridis", domain = data$var)(data$var)
sf::st_write(obj = data, dsn = "myfile.fgb", driver = "FlatGeobuf")
leafem::addFgb(file = "myfile.fgb", fill = TRUE, fillColor = NULL)

Examples

 if (interactive()) {
   library(leaflet)
   library(leafem)

   # via URL
   url = "https://raw.githubusercontent.com/flatgeobuf/flatgeobuf/3.0.1/test/data/UScounties.fgb"

   leaflet() %>%
     addTiles() %>%
     leafem:::addFgb(
       url = url
       , group = "counties"
       , label = "NAME"
       , popup = TRUE
       , fill = TRUE
       , fillColor = "blue"
       , fillOpacity = 0.6
       , color = "black"
       , weight = 1
     ) %>%
       addLayersControl(overlayGroups = c("counties")) %>%
       addMouseCoordinates() %>%
       setView(lng = -105.644, lat = 51.618, zoom = 3)
 }