# [R] Plot polygon in 3D with rgl

Remko Duursma remkoduursma at gmail.com
Mon May 10 01:56:15 CEST 2010

```Duncan,

thanks for the tip! I actually saw this 2D function but had no idea
how to use it in 3D. Works great.

Remko

-------------------------------------------------
Remko Duursma
Research Lecturer

Centre for Plants and the Environment
University of Western Sydney
Hawkesbury Campus
Richmond NSW 2753

Dept of Biological Science
Macquarie University
North Ryde NSW 2109
Australia

Mobile: +61 (0)422 096908
www.remkoduursma.com

On Mon, May 10, 2010 at 9:24 AM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 09/05/2010 6:41 PM, Remko Duursma wrote:
>>
>> Dear R-helpers, an rgl-ers in particular,
>>
>>
>> what is the easiest way to plot a section of a plane in 3D, that is
>> given by the xyz coordinates of the outline?
>>
>> Suppose I have a polygon - which I know for sure is a set of
>> coordinates on the same plane. One method I found is to use surf.tri
>> from the geometry package, and then plot the triangles with
>> rgl.triangles. This method is not perfect though, because it makes the
>> convex hull - no good for the polygon below.
>>
>>
>> Remko
>>
>> # Example polygon in 3D (matrix with tree columns x,y,z)
>> m <- structure(c(-24.71, -36.45, -59.54, -83.97, -112.63, -126.66,
>> -152.79, -171.04, -178.92, -183.71, -189.27, -191.56, -195.98,
>> -203.09, -207.89, -212.12, -216.92, -221.73, -210.58, -199.43,
>> -195.58, -175.38, -161.72, -152.09, -140.75, -123.63, -97.87,
>> -79.04, -69.63, -61.75, -54.08, -38.34, -30.47, -24.71, -15.44,
>> -13.33, -14.26, -17.39, -24.5, -31.92, -52.3, -70.45, -79.41,
>> -89.16, -102.08, -111.61, -119.76, -125.55, -128.56, -132.55,
>> -135.55, -138.55, -132.93, -127.31, -124.91, -125.78, -126.69,
>> -127.42, -124.38, -117.74, -105.69, -88.52, -79.94, -70.97, -59.43,
>> -34.75, -25.78, -15.44, 689.49, 686.54, 680.81, 674.79, 667.78,
>> 664.42, 658.27, 654.05, 652.25, 651.22, 650.06, 649.66, 648.7,
>> 647.04, 645.89, 644.91, 643.77, 642.63, 645.3, 647.98, 648.89,
>> 653.93, 657.35, 659.75, 662.52, 666.66, 672.86, 677.25, 679.44,
>> 681.24, 682.95, 686.44, 688.24, 689.49), .Dim = c(34L, 3L))
>>
>> # One (wrong) way
>> library(geometry)
>> tm <- t(surf.tri(m, delaunayn(m)))
>> plot3d(m[,1],m[,2],m[,3], type='l', col="black", size=2)
>> rgl.triangles(m[tm, 1], m[tm, 2], m[tm, 3],  col="green")
>>
>>
>
> There's a function triangulate() in the gpclib package that can triangulate
> a 2d polygon.  So you could pick two out of your three dimensions,
> triangulate those, then compute the 3rd coordinate from a fitted plane to
> the other two.  For example:
>
> library(gpclib)
> x <- m[,1]
> y <- m[,2]
> z <- m[,3]
> triangles <- triangulate(as(cbind(x,y), "gpc.poly"))
> zfit <- predict(lm(z ~ x + y), newdata=data.frame(x=triangles[,1],
> y=triangles[,2]))
> triangles3d(cbind(triangles, zfit), col="green")
>
> Duncan Murdoch
>

```