[R-sig-Geo] symbols on a map

[Edzer J. Pebesma]

Hi Susuma, I agree with the previous suggestions. I know that
Roger is away for a while, and although I know little about
pixmap I will give it a try. I do not think that pixmap currently
actively supports transparency, in the sense that it stores
red/green/blue+alpha channels. However, it does support
indexed bitmaps, which have an index "channel" and a colour table.
You may want to create such a pixmap, and then give it
colors that have an alpha value, as in:

 > library(sp)
 > bpy.colors(10,alpha=.5)
 [1] "#00003380" "#00009980" "#0000FF80" "#5000FF80" "#9F0FF080" "#EF42BD80"
 [7] "#FF758A80" "#FFA85780" "#FFDB2480" "#FFFF6080"

Here, #FF758A80 refers to hexadecimal encoding of
red (FF) green (75) blue (8A) and transparency (80), all
on a scale from 0 (=00) to 255 (=FF). If the pixmap
accepts this, the consequent plotting method may
again pick up the transparency (alpha) level.

I haven't tried, but it may as well work.

HTH,
--
Edzer


Susumu Tanimura wrote:

>Dear Drzyzga, Scott
>
>  
>
>>You might want to consider reading Paul Murrell's (2004) article, which
>>addresses the transparency issue.
>>    
>>
>
>Thank you for the information. Semitransparent on a map was
>successfully shown with command such as
>plot(Mapobject,fg=rgb(1,0,0,0.5)).  As for pixmap, I can not come up
>with idea to make symbol picture transparent.
>
>  
>
>>Also, empirical scatterplots and
>>variogram clouds yield so much more information when the densities of
>>overlapping data can be observed and considered.  
>>    
>>
>
>Since I am familiar to neither gstat nor geoR, I may be wrong but I
>think a background of plotted vector object is usually transparent.
>In this case, there is no problem.  The problem of pixmap is that
>a rectangular background of bitmap picture covers the basemap, and
>piles one another.
>
>Thanks.
>
>--
>Susumu Tanimura
>Dept. of Socio-environmental Medicine
>Inst. of Tropical Medicine, Nagasaki University
>TEL 095-849-7865 FAX 095-849-7867
>
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