Read what was drawn or edited on a map

Turns an input$<output_id>$sketch or input$<output_id>$edits event into an sf object. Both carry their features as Esri feature JSON, which is what arcgisutils::parse_esri_json() reads.

Usage

arc_sf(x)

Arguments

x

Defines which event to read, from input$<output_id>$sketch or input$<output_id>$edits.

Value

An sf object, or NULL when the event carried no features - a cleared sketch, or an edit that only deleted.

Details

A drawn shape is returned in longitude/latitude, since the view draws in Web Mercator and metres are rarely what the next line of R wants. Edited features come back in the layer's own coordinate reference system, the one the data frame was sent in.

Examples

# Inside a Shiny server:
if (interactive()) {
  observeEvent(input$map$sketch, {
    drawn <- arc_sf(input$map$sketch)
    print(sf::st_area(drawn))
  })
}