In coolbutuseless/threed: Three-Dimensional Object Transformations

suppressPackageStartupMessages({
  library(magrittr)
})
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

mesh3d adaptations

The threed package adapts/extends the mesh3d format to include the following:

• Meshes now support primitivetype of point and line (in addtion to the standard triangle and quad)
• Meshes with line segments will contain il. This is a 2 x n matrix giving the indices of the vertex of each end of the line segment.
• Meshes with point data will contain ip. This is a 1 x n matrix giving the index of the vertex of the point.
• A general properties data.frame can be included in the object. The number of rows in this data.frame must equal the total number of elements in the object.
• A transform_matrix is a 4x4 transformation matrix. If missing or NULL, then it is treated as the identity matrix.

Transforming mesh3d objects

• The supported object transformations are:
  • scale_by(obj, c(x, y, z))
  • translate_by(obj, c(x, y, z))
  • rotate_by(obj, angle, c(x, y, z))
  • `perspective_projection(obj, w, h, n, f)
• When applying a transform to an object, the object vertices are not immediately transformed.
• Instead, a mesh3d object now includes an extra transform_matrix element which keeps track of the transforms applied to this object.
• To actually update the vertex positions, call actualize_transformation on the object.

# A 2x2x2 cube centred at the origin
threed::mesh3dobj$cube 

# Transforming the cube only updates the `transform_matrix` of the object
threed::mesh3dobj$cube %>%
  threed::translate_by(c(x=0, y=1, z=1))

# Actualizing the transformation updates the vertices
threed::mesh3dobj$cube %>%
  threed::translate_by(c(x=0, y=1, z=1)) %>%
  actualize_transformation()

as.data.frame.mesh3d

The as.data.frame.mesh3d function will convert a mesh3d object into a very verbose data.frame.

This function first calls threed::actualize_transformation() to apply any outstanding transformations to the vertices.

The resulting data.frame can then be used to plot the 3d points, lines and polygons in ggplot2. It has the following columns by default:

• element_id - element index
• element_type - an integer from 1 to 4 indicating whether the element is a point, line, triangle or quad
• vorder - vertex ordering within element
• x,y,z - coorindates of vertex
• vertex - global index of this vertex
• vnx,vny,vnz - unit vector in direction of vertex normal
• fnx,fny,fnz - unit vector in direction of face normal
• fcx,fcy,fcz - coordinates of centroid of element
• zorder - zorder is used to control ggplot draw order. For polygons it is based upon fcz. For lines it is the smaller of the z coordinates. For points, it is the z coordinate of the point
• zorder_var - The value used to determine zorder
• hidden - by assuming the camera faces along the negative z-axis, any triangle or quad face which has a face normal which also points along the negative z-axis faces away from the camera and is hidden. Boolean value.

obj <- threed::mesh3dobj$cube

as.data.frame(obj)

coolbutuseless/threed documentation built on May 5, 2019, 7:08 a.m.