[R] Change position in package rgl

[Duncan Murdoch]

On 12/04/2014, 11:19 AM, Roland Rau wrote:
> Dear all,
>
> I am using package rgl and I want to change the position where I "stand".
> Maybe a small example might clarify what I am looking for:
>
>
> # Begininng of explanatory example
> library(rgl)
> data(volcano)
>
> # the example ?rgl.surface
> y <- 2 * volcano
> x <- 10 * (1:nrow(y))
> z <- 10 * (1:ncol(y))
> ylim <- range(y)
> ylen <- ylim[2] - ylim[1] + 1
> colorlut <- terrain.colors(ylen)
> col <- colorlut[ y-ylim[1]+1 ]
>
> rgl.open()
> rgl.surface(x, z, y, color=col, back="lines")
> ## now I have the nice volcano surface
> ## with rgl.viewpoint I can change the elevation
> ## and the angle from where I look at the rgl.surface
> # example of ?rgl.viewpoint
> start <- proc.time()[3]
> while ((i <- 36*(proc.time()[3]-start)) < 360) {
>    rgl.viewpoint(i,i/4);
> }
> # End of explanatory example
>
> What I am looking for (in this example) would be a way for me to "stand"
> on the crater of the volcano, looking in a specific direction. Is there
> something like a function where I can specify my coordinates (x,y,z) and
> angle and a zoom factor?

I think you could hack something like that (see the description in 
?par3d of how rendering is accomplished), but there's currently no 
support for it, and it wouldn't be easy, as currently P and M in that 
description are read-only quantities computed indirectly.  So you'd have 
to essentially trick rgl into producing the P matrix corresponding to 
the viewing position you want.

I am currently working on some changes that might make this easier, but 
they likely aren't going to be released for several months.

Duncan Murdoch