[R] transparency using plot+points with sp classes

[David Winsemius]

On Dec 28, 2011, at 7:13 AM, Ana wrote:

> How can I make one point graphics with transparency
>
> These are all sp classes:
>
> plot(polygons_area,axes=TRUE,asp=1.5,main="Title",xlab="Latitude",
> ylab="Longitude")
> points(observations2000,type = "p",pch=21,col="green")
> points(observation1999,type = "p",pch=21,col="blue")
> points(reference.points,type = "p",pch=21,col="red")
>
> how can I add transparency to one of the point graphics, for example
> points(observation1999,type = "p",pch=21,col="blue")  ?

Read the Details section of :

?rgb

-- 
David Winsemius, MD
West Hartford, CT