Geometry primitives

Alejandro Morales

Centre for Crop Systems Analysis - Wageningen University

using VirtualPlantLab
import ColorTypes: RGBA # for the color of each mesh
import GLMakie # For 3D rendering (native OpenGL backend)

VPL offers several functions to created 3D meshes that correspond to common geometric shapes (i.e., primitives). They are meant to represent simple geometry elements or to build more complex geometries through the use of turtle-based procedural geometry. For that reason, there are two versions of each primitive constructor: one that constructs the mesh directly (with a standard location and orientation) and one that feeds the mesh to a turtle. The former is meant to be used when manually adding geometries to am existing scene (e.g., soil, structural elements) whereas the latter is mean to be used within the feed methods associated to nodes in a graph. Additional functions are able to translate and rotate these meshes to the desired location and orientation (see API of the Geometry module for details).

Below, the functions for direct construction of the meshes are listed. The turtle-based constructor have the same argument plus the turtle arugment itself as well as optional arguments for color and optical materias (see API of the Geometry module for more details).

Each primitive is visualized using the render function form VPL. These 3D visualizations keep the axes to help understand what the standard location and orientation are (use axes = false to turn off). They also set normals = true and wireframe = true to highlight how the mesh is partitioned into triangles and the normal vectors of each triangle (this is important for the ray tracer and when exporting meshes out of VPL). All meshes are rendered in green assuming 50% transparency (color = RGBA(0,1,0,0.5)). Note that one must use transparency = true to ensure that the transparency is enabled when rendering the mesh.

Triangle

turtle = Turtle()
p = Triangle!(turtle; length = 1.0, width = 1.0, colors = rand(RGBA))    
render(Mesh(turtle), wireframe = true)

Rectangle

turtle = Turtle()
p = Rectangle!(turtle; length = 1.0, width = 1.0, colors = rand(RGBA)) 
render(Mesh(turtle), wireframe = true)

Trapezoid

turtle = Turtle()
p = Trapezoid!(turtle; length = 1.0, width = 1.0, ratio = 0.5, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Ellipse

turtle = Turtle()
p = Ellipse!(turtle; length = 1.0, width = 1.0, n = 30, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Axis-aligned bounding box

turtle = Turtle()
p = BBox(Vec(0.0, 0.0, 0.0), Vec(1.0, 1.0, 1.0))
Mesh!(turtle, p, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Cube

Solid version

turtle = Turtle()
p = SolidCube!(turtle; length = 1.0, width = 1.0, height = 1.0, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Hollow version

turtle = Turtle()
p = HollowCube!(turtle; length = 1.0, width = 1.0, height = 1.0, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Primitives with (semi-)circular bases

The following primitive types share a parameter n, which is the number of triangles to discretize the cylinder into. The lower is number n, cicle base shape will be more rough (e.g., n = 20, base shape is a pentagon). The higher is number n, cicle base shape will be more smooth (e.g., n = 80, base shape is a circle). The same analogy also apply to ellipse; see above, in this case n = 5 the shape is a pentagon, and n = 30 the shape is elipsoidal.

Cylinder

Solid version

turtle = Turtle()
p = SolidCylinder!(turtle; length = 1.0, width = 1.0, height = 1.0, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Hollow version

turtle = Turtle()
p = HollowCylinder!(turtle; length = 1.0, width = 1.0, height = 1.0, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Frustum

Solid version

turtle = Turtle()
p = SolidFrustum!(turtle; length = 1.0, width = 1.0, height = 1.0, ratio = 0.5, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Hollow version

turtle = Turtle()
p = HollowFrustum!(turtle; length = 1.0, width = 1.0, height = 1.0, ratio = 0.5, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Cone

Solid version

turtle = Turtle()
p = SolidCone!(turtle; length = 1.0, width = 1.0, height = 1.0, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)

Hollow version

turtle = Turtle()
p = HollowCone!(turtle; length = 1.0, width = 1.0, height = 1.0, n = 80, colors = rand(RGBA))
render(Mesh(turtle), wireframe = true)