`as.mesh3d.default.Rd`

The `as.mesh3d`

generic function converts various objects
to `mesh3d`

objects.

The default method takes takes a matrix of vertices
as input and (optionally) merges repeated vertices, producing a `mesh3d`

object as output. It will contain either triangles or quads or segments or points
according to the `type`

argument.

If the generic is called without any argument, it will pass
all RGL ids from the current scene to the
`as.mesh3d.rglId`

method.

- x, y, z
For the generic,

`x`

is the object to convert. For the default method,`x`

,`y`

and`z`

are coordinates. Any reasonable way of defining the coordinates is acceptable. See the function`xyz.coords`

for details.- type
What type of things should be in the mesh? Tries this list in order until it finds one that works.

- smooth
If

`TRUE`

,`addNormals`

will be called on the mesh object to make it render smoothly.- tolerance
The numerical tolerance to be used in

`all.equal`

to determine whether two vertices should be merged.- notEqual
If not

`NULL`

, an n by n matrix of logical values, where n is the number of vertices as input.`TRUE`

entries indicate that the corresponding pair of vertices should not be merged even if they appear equal.- merge
Should apparently equal vertices be merged?

- ...
- triangles
Deprecated. If present,

`TRUE`

indicates`type = "triangles"`

and`FALSE`

indicates`type = "quads"`

.

The motivation for this function is the following problem: I was asked whether RGL could render a surface made up of triangles or quadrilaterals to look smooth. It can do that, but needs normals at each vertex; they should be the average of the normals for each polygon sharing that vertex. Then OpenGL will interpolate the normals across the polygons and give the illusion of smoothness.

To do this, it needs to know which polygons share each vertex. If the
surface is described as a list of triangles or quadrilaterals, that
means identifying vertices that are in multiple polygons, and converting
the representation to a `"mesh3d"`

object (which is a matrix of vertices
and a matrix of vertex numbers making up triangles or quads). Then the
`addNormals`

function will add the normals.

Sometimes two polygons will share vertices (within numerical
tolerance) without the user wanting them to be considered internal to
the surface, or might want one sharp edge in an otherwise smooth
surface. This means I needed a way to declare that two vertices from
the original list of vertices in the triangles or quads are "not equal",
even when they test numerically equal. That's what the `notEqual`

matrix specifies.

A `"mesh3d"`

object with the same faces as in the
input, but (if `merge=TRUE`

) with vertices that test equal to
within `tolerance`

merged.

```
xyz <- matrix(c(-1, -1, -1,
-1, 1, -1,
1, 1, -1,
1, -1, -1,
-1, 1, -1,
-1, 1, 1,
1, 1, 1,
1, 1, -1,
1, -1, -1,
1, 1, -1,
1, 1, 1,
1, -1, 1), byrow = TRUE, ncol = 3)
mesh <- as.mesh3d(xyz, type = "quads", col = "red")
mesh$vb
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7]
#> [1,] -1 -1 1 1 -1 1 1
#> [2,] -1 1 1 -1 1 1 -1
#> [3,] -1 -1 -1 -1 1 1 1
#> [4,] 1 1 1 1 1 1 1
mesh$ib
#> [,1] [,2] [,3]
#> [1,] 1 2 4
#> [2,] 2 5 3
#> [3,] 3 6 6
#> [4,] 4 3 7
open3d()
shade3d(mesh)
# Stop vertices 2 and 5 from being merged
notEQ <- matrix(FALSE, 12, 12)
notEQ[2, 5] <- TRUE
mesh <- as.mesh3d(xyz, type = "quads", notEqual = notEQ)
mesh$vb
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
#> [1,] -1 -1 1 1 -1 -1 1 1
#> [2,] -1 1 1 -1 1 1 1 -1
#> [3,] -1 -1 -1 -1 -1 1 1 1
#> [4,] 1 1 1 1 1 1 1 1
mesh$ib
#> [,1] [,2] [,3]
#> [1,] 1 5 4
#> [2,] 2 6 3
#> [3,] 3 7 7
#> [4,] 4 3 8
```