Difference between revisions of "BRL-CAD Primitives"

From BRL-CAD
(arbn: Added more detail about how the coefficients and distances interplay)
(rcc)
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Right circular cylinder, special case of tgc
 
Right circular cylinder, special case of tgc
 
;Handled by: in make form(tgc) create
 
;Handled by: in make form(tgc) create
;Arguments: vertex ,  
+
;Arguments: vertex , height , radius
 +
 
 
== rec ==
 
== rec ==
 
Right elliptical cylinder, special case of tgc
 
Right elliptical cylinder, special case of tgc

Revision as of 12:32, 8 April 2010


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.

See also A Survey of Implicit Constraints in Primitives

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.

The solid is constructed by N sets of plane coefficients and distance magnitudes, that define space which is ~outside~ the solid. The coefficients define a vector whose normal is a plane parallel to the face of the solid. The surface of the solid is at the perscribed distance along this vector.

The distances may be negative and are used when a face lies on the opposite side of the origin as the tip of its vector. An example is if the left side of a box lies on the positive X axis. In this case, because the left side is being defined, the vector points left (coefficients -1 0 0), but since the point is on the positive X axis its distance is opposite its vector and therefore negative.

Handled by
make in create
Arguments
Number of planes
xyz direction vector and distance 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
Example with negative distance
in arbn2.s arbn 6 1 0 0 100 -1 0 0 -10 0 1 0 200 0 -1 0 -10 0 0 -1 0 0 0 1 1.5
...is equivalent to...
in rpp.s rpp 10 100 10 200 0 1.5

box

Special case of arb8

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

raw

Right Angle Wedge, special case of arb6

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

rpp

Rectangular Parallelpiped, 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 , height , radius

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, special case of tgc

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

derived from 2d

extrude

Extrusion of a 2-d sketch

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

revolve

Revolution of a 2-d sketch

Handled by
in
Arguments
vertex, revolution axis, vector in start plane, angle, sketch

dsp

Handled by
in create
Arguments
data type (f|o), datasource, count of length and width, interpolation type, cut direction, cell size, unit elevation

ebm

extruded bit map

Handled by
in form create
Arguments
filename, width and height in cells, extrusion distance,

See also EBM tutorial.

The extruded bitmap (also referred to as EBM) is a solid based on a greyscale bitmap. The bitmap is an array of unsigned char values, see bw(5), and is extruded by some distance. The EBM solid requires the dimensions of the bitmap file (height and width in bytes), an extrusion length, and a transformation matrix to position the EBM. Each byte in the bitmap file is treated as the base of a cell that is extruded by the specified extrusion length. If the value of the byte is non­zero, then that cell is considered solid.

hf

Height field

Handled by
none?
Status
depreciated, use dsp instead


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)


nurb

Non-uniform rational b-spline

Handled by
none?

spline

surface splines

Handeld by
 ?

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
See also
BoT

poly

polysolid

Handled by
none?
Status
depreciated, use bot instead

Other

Sketch

2d outline

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

grip

Grip -- support for joints, non-geometric (does not show in rt)

Handled by
in make form create

Arguments:

Center
normal vector
magnitude

half

halfspace

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

A half space is the portion of space on one side of a plane. It is represented by its boundary (the plane) and its outward-pointing normal vector.

binunif

Uniform-array binary object

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