mouseHandler for addGeotiff (geoblaze.js)

[trafficonese]

Using geoblaze.js allows to get the raster value at a certain lat/lng. I modified leaflet's mouseHandler to allow click and mousemove for addGeotiff. It could also be included in addCOG but so far I didn't manage to use that function successfully.

I'm not sure if you want to include the new dependency (~1MB) or if you have something else in mind already. So feel free to close it or request additional changes.

Shiny example!

library(leaflet)
library(leafem)
library(stars)
library(shiny)

tif = system.file("tif/L7_ETMs.tif", package = "stars")
x1 = read_stars(tif)
x1 = x1[, , , 3] # band 3
tmpfl = tempfile(fileext = ".tif")
write_stars(st_warp(x1, crs = 4326), tmpfl)
myCustomJSFunc = htmlwidgets::JS("
    pixelValuesToColorFn = (raster, colorOptions) => {
      const cols = colorOptions.palette;
      var scale = chroma.scale(cols);

      if (colorOptions.breaks !== null) {
        scale = scale.classes(colorOptions.breaks);
      }
      var pixelFunc = values => {
        let clr = scale.domain([raster.mins, raster.maxs]);
        if (isNaN(values)) return colorOptions.naColor;
        return clr(values).hex();
      };
      return pixelFunc;
    };")

ui <- fluidPage(
leafletOutput("map"),
splitLayout(cellWidths = c("50%", "50%"),
  div(h4("Click"),verbatimTextOutput("click")),
  div(h4("Mouseover"),verbatimTextOutput("mouseover"))
)
)

server <- function(input, output, session) {
output$map <- renderLeaflet({
  leaflet() %>%
    addTiles() %>%
    addGeotiff(
      file = tmpfl
      , group = "geotiffgroup"
      , layerId = "somelayerid"
      , opacity = 0.9
      , colorOptions = colorOptions(
        palette = grey.colors
        , na.color = "transparent"
      )
      , pixelValuesToColorFn = myCustomJSFunc
    )
})
output$click <- renderPrint({
  txt <- req(input$map_georaster_click)
  print(txt)
})
output$mouseover <- renderPrint({
  txt <- req(input$map_georaster_mousemove)
  print(txt)
})
}
shinyApp(ui, server)