Great !
Thanks !
Patrick
Roger Bivand a écrit :
On Thu, 5 Aug 2010, Patrick Giraudoux wrote:
Hi,
I was wondering if it is possible to manage color transparency with
image.SpatialGridDataFrame ? Eg to export png that could be imported
into Google Earth in the way indicated in Bivand et al. pp 97-98
(functions kmlOverlay and GE_SpatialGrid of maptools). If yes how ?
NAs are set transparent by default (on output devices supporting
transparency). Other values may be given an alpha of less than 1 -
here a single value for all:
library(sp)
data(meuse.grid)
coordinates(meuse.grid) = c("x", "y")
gridded(meuse.grid) = TRUE
image(meuse.grid["dist"], col=heat.colors(12),
main = "Distance to river Meuse")
image(meuse.grid["dist"], col=heat.colors(12, alpha=0.5),
main = "Distance to river Meuse")
By setting the col= vector manually, it is possible to assign a
different alpha value for each element, but it may be difficult to
obtain a satisfactory visual impression consistently across output
devices. See col2rgb() and rgb(). See also the colorspace package for
a sophisticated treatment, and the use of hcl palettes, and the hsv()
function. All of these can help in constructing a colour vector to
pass to image.SpatialGridDataFrame().
Hope this helps,
Roger
Patrick
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