[R] RGL plot : lighting problem when triangle3d and persp3d are used in the same plot

[Duncan Murdoch]

On 28/08/2012 7:49 AM, Stephane Chantepie wrote:
> thanks for the reply
>
> I am sorry but I do not have any skills in C++
>
> Nevertheless, I found a solution to my problem... By using another package
>   "misc3d" and more precisely the association of the two
> functions drawScene.rgl and surfaceTriangles
>
> drawScene.rgl(surfaceTriangles(x,y,z,color="gray",smooth=1))
>
> The idea behind this trick is to transform the matrix in triangle surfaces
> before to plot them.
>
> I hope this could help someone else

Thanks, I didn't know about those functions.

Duncan Murdoch

>
> cheers
>
>
>
> 2012/8/27 Duncan Murdoch <murdoch.duncan at gmail.com>
>
> > On 27/08/2012 1:47 PM, Stephane Chantepie wrote:
> >
> >> Dear all,
> >>
> >> I have tried to plot a triangular matrix with the function persp3d(rgl).
> >>
> >> for example
> >>
> >> z=rbind(c(1,NA,NA,NA),c(5,3,**NA,NA),c(4,2,9,NA),c(8,6,5,11)**)
> >> x=1:4
> >> y=1:4
> >> persp3d(x,y,z,color="gray")
> >>
> >> The two extreme points are not plotted (value=1 and value=10). It seems
> >> because the half of the matrix have 'NA'  and perp3d need planar
> >> quadrilateral face. So I decided to use the function triangle3d to
> >> integrate these points into the scene.
> >>
> >> So, for the first point I did :
> >>
> >> triangles3d(x=c(1,2,2),y=c(1,**1,2),z=c(1,5,3)) and it worked
> >>
> >> But a problem remains because the light movment on this triangle looks
> >> independant and I did not find how to solve this issue.
> >>
> >> How can I prefectly integrate this triangle into the scene?
> >>
> >
> > You need to set the normals at the vertices that are shared with the
> > persp3d vertices.  rgl internally averages the normals to the pieces making
> > up each facet; you don't have enough access to the internals to do that.
> >  (You'd want to change the normal on the surface, as well, because your
> > triangles should participate in the averaging.)
> >
> > But you could set the normals to the new triangle to match the normal to
> > the one it joins to, and get something that looks sort of okay.  It's not
> > going to be a simple calculation:  you need to figure out the coordinates
> > of the edges joining at those vertices, take a cross product, and use that.
> >  See ?rgl.primitive for how to send the normals to points3d; I think the
> > normals need to be length 1, but that may be forced internally.
> >
> > If you were really ambitious, you could take a look at the C++ code that
> > draws the surface, and contribute code to smooth the edge properly; I think
> > it would be an improvement over the current behaviour, but it is tedious to
> > write.
> >
> > Duncan Murdoch
> >
>