Hello,
I can't seem to add transparency to any color ramp I create using
colorRampPalette(). Can someone tell me if it is possible to create transparent
colour ramps?
I am attempting to map shaded relief under elevation data. I know I can use the
terrain.colors() with the alpha option, but I would prefer to create my own
colour ramp using more vibrant colours.
My most recent attempt at doing this involved generating multiple rgb colours
with transparency (alpha = 0.5) and then combining these colours using
colorRampPalette(). I am able to use the resulting colour ramp, but it has no
transparency.
# Make terrain colour ramp
rgb7 <- rgb(red=0, green=255, blue=77, alpha = 0.5, maxColorValue = 255)
rgb8 <- rgb(red=26, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
rgb9 <- rgb(red=128, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
rgb10 <- rgb(red=230, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
rgb11 <- rgb(red=255, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
rgb12 <- rgb(red=255, green=229, blue=60, alpha = 0.5, maxColorValue =
255)
rgb13 <- rgb(red=255, green=219, blue=119, alpha = 0.5, maxColorValue =
255)
rgb14 <- rgb(red=255, green=224, blue=178, alpha = 0.5, maxColorValue =
255)
rgb15 <- rgb(red=255, green=255, blue=255, alpha = 0.5, maxColorValue =
255)
terraincolours <- colorRampPalette(c(rgb7, rgb8, rgb9, rgb10, rgb11,
rgb12, rgb13, rgb14, rgb15))
# Plot map
image(terrain, col = shadecolours(512), axes = TRUE) # plots the shaded
relief
#image(dem, col = terrain.colors(512, alpha = 0.5), add = TRUE) # this
option works, but I don't like the colours in the terrain.colors pallet.
image(dem, col = terraincolours(512), add = TRUE) # draws the elevation
data with no transparancy and it won't accept an alpha value
Thank you,
James
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