# Difference between revisions of "BRL-CAD Primitives"

These are primitive objects that can be created in mged.

Objects can be created in any of the following ways: (note: are there more? get? load from file?)

make
the mged make command creates the object with default dimensions
in
the mged in command interactively prompts for dimensions not already supplied as arguments
form
the graphical primitive editor form (* some objects not fully supported)
create
the graphical create menu

When an object is selected from the create menu, you are prompted for a name, and then dropped into the primitive editor form; however, if the objec type has no form, create will do about the same as make. Some derivative objects do not have their own form, and the primitive editor will use the base object's form. Most parameters (including ones not editable from a form) have special items on the edit menu.

# Arbs

Objects with an arbitrary number of points and flat faces...

## arb8

Arbitrary straight-edged shape with 8 vertices.

Handled by
make in form create
Arguments
8 Vertices in the following order: 1234 vertices for the front face, starting at bottom left, counterclockwise; then 5678 vertices for the rear face, starting at bottom left, counterclockwise.
Example
```in unitcube.s arb8  0 0 0  1 0 0  1 0 1  0 0 1  0 1 0  1 1 0  1 1 1  0 1 1
```

creates the unit cube (first vertex at the origin, extends for 1 unit in x, y and z direction).

## arb7

Special case of arb8, except with point 8 merged into point 5, making the left face triangular

Handled by
make in form(arb8) create

## arb6

Arbitrary straight-edged shape with 6 vertices, special case of arb8.

Handled by
make in form(arb8) create
Arguments
6 Vertices in the following order: 1234 vertices for the front face, starting at bottom left, counterclockwise; then back edge is 5 on bottom, 6 on top. Top and bottom faces are triangles.
Example
```in arb6.s arb6 1 -1 -1   1 1 -1   1 1 1  1 -1 1  -1 0 -1  -1 0 1
```

## arb5

special case of arb8.

Handled by
make in form(arb8) create

## arb4

special case of arb8.

Handled by
make in form(arb8) create

## arbn

Arbitrary solid bounded by N planes

Handled by
make in create
Arguments
Number of planes
xyz direction vector and normal for each plane
Example

in arbn.s arbn 8 1 0 1 1 -1 0 0 1 0 1 0 1 0 -1 0 1 0 0 1 1 0 0 -1 1 0.5 0.5 0.5 1 -0.5 -0.5 -0.5 1

## box

Special case of arb8

Handled by
in form(arb8)
Arguments
vertex of first corner
direction vectors for height, width, and depth

## rpp

Special case of arb8

Handled by
make in form(arb8) create
Arguments
xmin xmax ymin ymax zmin zmax

# Ellipsoids

## ell

Ellipsoid

Handled by
make in form create
Arguments
vertex point, at the center
vectors A B C describing the radii of the ellipses; A points front, B points right, C points up.

Example:

```in ell.s ell 0 0 0  0 -1 0  1 0 0  0 0 1
```

## sph

Sphere, special case of the ellipsoid, with vectors A B and C all the same magnitude (radius).

Handled by
make in form(ell) create

Arguments:

vertex point, at the center
radius

## ellg

Special case of ellipsoid

Handled by
in form(ell)
Arguments
two foci points, and axis length

## ell1

Special case of ellipsoid

Handled by
in make form(ell) create
Arguments
vertex, vector A, radius of revolution

## ehy

Elliptical hyperboloid

Handled by
make in form create
Arguments
vertex, perpendicular vectors Height and (A,r_1) major axis, (r_2) magnitude of vector B, (c) apex to asymptotes distance

## epa

Elliptical paraboloid

Handled by
in make form create

# Cones and Cylinders

## tgc

Truncated general cone

Handled by
in make form create
Arguments
vertex, vectors H A B, magnitudes of vectors C D

## rcc

Right circular cylinder, special case of tgc

Handled by
in make form(tgc) create
Arguments
vertex ,

## rec

Right elliptical cylinder, special case of tgc

Handled by
in make form(tgc) create
Arguments
vertex, height vector, radius

## rhc

Right hyperbolic cylinder

Handled by
in make form create
Arguments
vertex, perpendicular vectors for Height and B, (r) rectangular half width, (c) apex to asymptote distance,

## rpc

Right parabolic cylinder

Handled by
in make form create
Arguments
vertex, perpendicular vectors for Height and B, (r) rectangular half width

## tec

Truncated elliptical cone, special case of tgc

Handled by
in make form(tgc) create
Arguments
Vertex, vectors Height, A, B

## trc

Truncated right circular cone

Handled by
in make form(tgc) create
Arguments
Vertex, Height vector, radius of base and top

# Other solids

## tor

Torus

Handled by
in make form create
Arguments
vertex, normal vector, radius of revolution, tube radius

## eto

Elliptical torus

Handled by
in make form create
Arguments
vertex, normal vector, radius of revolution, vector C, (r_d) magnitude of semi-minor axis

## part

Conical particle

Handled by
in make create
Arguments
vertex, height vector, radius at v, radius at h

The particle solid is a lozenge-shaped object defined by a vertex, a height vector and radii at both ends. The body of the particle is either a cylinder or a truncated cone, depending on the values of the radii. Each end of the particle is a hemisphere of the specified radius.

## nmg

n-Manifold geometry solid (non-manifold geometry?)

Handled by
make create

## pipe

Hollow and solid pipes and wires

Handled by
in make create
Arguments
# points, for each point: location, inner and outer diameters, bend radius

## ars

Arbitrary rectangular solid

Handled by
in make create

Solids of type 'ars' (Arbitrary Faceted Solids) are defined using "waterlines". The following figure consists of a start point, some number of intermediate polygons, and an ending point. Each of the intermediate polygons have the same number of vertices and the vertices are numbered 1 thru N. In addition to the intermediate polygons a line will be created that begins at the start point, goes through each polygon at its vertex numbered 1, and terminates at the end point. This is repeated for each polygon vertex 2 thru N. The start point, polygons, and end point are each a "waterline".

<need an image here to illustrate the concept>

the ars shape takes the following values as input:

• The number of points per waterline (the number of vertices on each intermediate polygon)
• The number of waterlines (the number of intermediate polygons plus 2)
• X, Y, and Z for a starting point (the first waterline)
• for each interior polygon (an intermediate waterline)
• for each point on the polygon
• X, Y, and Z for the point on the polygon
• X, Y, and Z for an ending point (the last waterline)

For example, the command:

in x.1 ars 4 6 0 0 3 1 1 3 1 -1 3 -1 -1 3 -1 1 3 1 1 1 1 -1 1 -1 -1 1 -1 1 1 1 0 -1 0 -1 -1 -1 0 -1 0 1 -1 1 0 -3 0 -1 -3 -1 0 -3 0 1 -3 0 0 -3

Will produce a square bar with a tapered 1/8 turn twist in the middle. Of course, more waterlines in the twist and more points per waterline would make the twist smoother.

Example ARS

The parameters to the above ars command can be dissected as:

4 : number of points per waterline (i.e. intermediate polygons have 4 vertices)
6 : number of waterlines (four intermediate polygons plus the two endpoints)
0 0 3 - the center of the top end of the bar
1 1 3 1 -1 3 -1 -1 3 -1 1 3 : a 2x2 square in the xy plane at z offset 3
1 1 1 1 -1 1 -1 -1 1 -1 1 1 : a 2x2 square oriented the same as the first but at z offset 1
1 0 -1 0 -1 -1 -1 0 -1 0 1 -1 : a 2x2 square at a 45 degree rotation from the first squares at z offset -1
1 0 -3 0 -1 -3 -1 0 -3 0 1 -3 : a 2x2 square at a 45 degree rotation from the first squares at z offset -3
0 0 -3 : the center of the bottom end of the bar

## metaball

Handled by
in make form(*) create
Arguments
render method, threshold, number of points, location and field strength for each point (and blobbiness/goo factor)

## extrude

Extrusion of a 2-d sketch

Handled by
in make form(?) create
Arguments
vertex, perpendicular vectors Height A B, sketch

Handled by
in create

## hf

Height field

Handled by
none?
Status
depreciated, use dsp instead

## nurb

Non-uniform rational b-spline

Handled by
none?

## vol

volume / voxel

Handled by
in
Arguments
filename, xyz dimensions of file (in voxels), lower and upper threasholds, xyz dimensions of a cell

The vol solid is defined by a 3-dimensional array of unsigned char values. The solid requires a file of these values, the extent of the file (in bytes) in each dimension, the size of each cell, and high and low thresholds. Any value in the file that is between the thresholds (inclusive) represents a solid cell.

## bot

Bag of triangles

Handled by
in make create (not edit!)
Arguments
number of verticies, number of triangles, mode (1=surface 2=solid 3=plate), triangle orientation mode (1=unoriented 2=counter-clockwise 3=clockwise), each vertex, vertex index of each triangle

Note: no provisions in the edit menu to adjust this object!

extruded bit map

Handled by
in create

surface splines

Handeld by
?

# Other

## Sketch

2d outline

Handled by
make form(sketch editor) create
See also
sketch

## grip

Grip -- support for joints

Handled by
in make form create

Arguments:

Center
normal vector
magnitude

## half

halfspace

Handled by
in make form create
Arguments
Normal, distance from origin

## binunif

Uniform-array binary object

Handled by
in create (not edit!)
Arguments
minor type (fdcsiLCSIL), data file, number of values