CODEWITHSUNDEEP
rplot
FFI
FFI

Reputation: 402

Join overlapping circles using R

I want to draw circles with semitransparent colour on top of a map (showing prevalence), the colour at overlap areas is too heavy to show the background image, the code am using is too long to put here, but for circles am using:

symbols(data[,c(9, 10)], 
    circles = 5/(pi * a.rad * cos(atan(b.rad / a.rad * tan((data[,10])*pi/180)))/180000), 
    fg = NULL, 
    bg = rgb(0, 1, 0, 0.18),
    inches = F,  
    add = T)

I want to joint circles to plot them with the same "transparent" colour, is there some way to do this using R? Or is there any other alternative using R*?

*Please note: The maps am using are develped using R, and I can't use other program to develop them.

Upvotes: 0

Views: 683

Answers (1)

Carl Witthoft
Carl Witthoft

Reputation: 21532

There's no simple way, since you're plotting a series of circles. If you don't demand the fill color be consistent, you could set the alpha value to a very small level. To get a consistent fill color, you'll have to calculate the intersection areas of the circles and plot those areas as well as the nonintersection areas (instead of plotting circles). If you have multiple overlapping circles, you can see that will become a computational nightmare.

My personal recommendation is to plot with the smallest visible alpha value so that the worst-case overlap area doesn't obscure the map. This has the side-effect of clearly indicating the density of overlap areas.

Upvotes: 1

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