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ASC-NMG(1)

NAME

asc-nmg - convert an ASCII NMG description to a BRL-CAD database

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SYNOPSIS

asc-nmg [-h | -?] [filein | -] [fileout]

DESCRIPTION

asc-nmg reads a simple ASCII description of an n-manifold geometry (NMG) solid and writes a binary BRL-CAD geometry database (.g) containing the resulting NMG object. The input is not a standard BRL-CAD .asc geometry database; it is a line-oriented list of loops and vertices (see below).

If filein is omitted or given as -, the description is read from standard input. If fileout is omitted, the database is written to a file named nmg.g in the current directory. The output database always contains a single NMG solid named s.nmg inside a region named r.nmg.

The ASCII input consists of whitespace-separated tokens of the following forms:

To start a new outer (counter-clockwise) loop for a face:

l

To start a new "hole" (inner) loop in the current face:

l hole

To define a vertex and its coordinates in the current loop:

v# x y z

where # is an integer vertex number (e.g. v0 or v1) and x, y, z are its coordinates.

To reuse a previously defined vertex in the current loop, omit the coordinates:

v#

To extrude the first face by a vector:

e x y z

where x, y, z form the extrusion vector.

If an extrusion vector is supplied, the first described face is extruded to form a solid; this is intended for the case where exactly one face is described. Supplying an extrusion vector when more than one face is present may produce erroneous results. Otherwise, enough faces must be described to form a closed shell. Each run of asc-nmg produces a single NMG object.

OPTIONS

-h, -?

Print a usage message and exit. (asc-nmg takes no other options; all remaining arguments are interpreted as file names.)

EXAMPLES

Example 1. Extruding a face into a solid

With filein.txt containing a single face plus an extrusion vector:

l
	e	-1 0 0
	v0	1 -1 -1
	v1	1 1 -1
	v2	1 1 0
	v3	1 0 0
	v4	1 0 1
	v5	1 -1 1

the command:

$ asc-nmg filein.txt sample.g

extrudes the 'L'-shaped face along the vector (-1, 0, 0) to build a solid NMG object in sample.g, which can then be raytraced with rt(1) or viewed in mged(1).

Example 2. Creating a face with a hole and converting to facetized geometry

A square outer loop with a square inner hole loop (inner loop wound opposite to the outer loop):

l
    v0 0 0 0
    v1 10 0 0
    v2 10 10 0
    v3 0 10 0
l hole
    v4 2 2 0
    v5 8 2 0
    v6 8 8 0
    v7 2 8 0
$ asc-nmg square_with_hole.txt square.g
$ mged square.g facetize s.nmg bot.nmg

The first command produces a single planar NMG face containing a square hole; the second converts that NMG into a BoT primitive for further processing.

SEE ALSO

brlcad(1), mged(1), rt(1), g-stl(1), asc2g(1)

AUTHOR

BRL-CAD Team

This software is Copyright (c) 1989-2026 by the United States Government as represented by U.S. Army Research Laboratory.

BUG REPORTS

Reports of bugs or problems should be submitted via electronic mail to devs@brlcad.org