tonerToTrans function

Convert RGB maps to semi-transparent

Stamen-toner maps are 3-layer RGB rasters, which are converted to single-layer rasters with indexed colours with whites becoming transparent.

tonerToTrans(x,  pattern="(red|green|blue)$", power = 0.5,
        col='black',  threshold=Inf,  mostCommon=1)

Arguments

• x: A RasterStack with RGB colours, such as from openmap with path='stamen-toner'
• pattern: string passed to grep to find RGB layers.
• power: Values below 1 increase opacity, above 1 increases transparency
• col: colour for resulting map
• threshold: colours above this value are transparent
• mostCommon: integer vector, the most common colours are converted to transparent

Returns

A SpatRast with indexed colours

Author(s)

Patrick Brown

See Also

openmap

Examples

origMap = openmap(
           c(-11, 9),
          path='cartodb-nolabels',   
                buffer=2, verbose=TRUE
        )

        oldpar= map.new(origMap, bg='green')
        plot(origMap, add=TRUE)
        
        transMap = tonerToTrans(origMap, mostCommon=1)
        names(transMap)
  map.new(transMap, bg='green')
        plot(transMap, add=TRUE)


        par(oldpar)