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LGT(1)				    BRL-CAD				LGT(1)

       lgt - produce a shaded image of an model

       lgt [options...]	model.g	objects...

       Lgt is an image rendering tool for the mged(1) solids modeling data
       base. The program can run interactively or detached from	a terminal
       session (batch mode). The interactive user interface consists of	a
       terminal	independent pop-up hierarchical	menu system (though IRIS users
       have the	option of using	the mouse-driven graphics menus	instead). The
       experienced user	may wish to exit this menu system (by typing a `q')
       and use the single-letter command interface as described	below. For
       information on the hierarchical menus and detailed information on the
       commands	and overall usage of lgt please	refer to the paper The "lgt"
       Lighting	Model which is included	in the BRL-CAD documentation.  Note
       that specifying the viewing direction involves setting up light source
       zero, see the L command below for more information. There are numerous
       command-line options.

	   Set the number of degrees of	roll on	the grid to n. This is a
	   rotation of the viewing grid	about the viewing axis.

	   Set over-sampling factor to n. This is a simple anti-aliasing
	   technique which ray traces an n by n	array of pixels	and then
	   outputs a linear average of the result.

       -b"R G B"
	   Set the background color to R G B which are intensity values	from 0
	   to 255 of the red, green, and blue channels respectively.

	   Set the tracking-cursor flag	to n. When set to non-zero, this
	   causes an arrow cursor to point at the current scan line being ray
	   traced, assuming that a graphics device is being used. The default
	   is to disable the tracking-cursor.

       -d"x y"
	   Set automatic mapping offsets to x and y in the IR Module.

       -t"x y"
	   Set the grid	translation to x and y.	This offsets the grid within
	   the grid plane (perpendicular to the	viewing	axis).

       -D"x y"
	   Set the image translation to	x and y. This offsets the image
	   relative to the display origin.

	   Set the debug flag to n. This flag is for the developer/maintainer
	   of lgt(1) and librt(3), and sets a hexadecimal bitmask to turn on
	   or off diagnostics.

	   Specify the distance	from the origin	of the grid to the model
	   centroid as n millimeters. This command will	interact with the -p
	   option. If perspective is set to a positive number, the
	   user-specified grid distance	is ignored, because automatic
	   perspective adjusts both the	grid and observer distances according
	   to the desired degree of perspective. Conversely, if	perspective is
	   negative, the user-specified	grid distance, coupled with the
	   observer distance and the view size,	will effect the	apparent
	   degree of perspective. If perspective is set	to zero, the grid
	   distance will be used to position the grid; if the distance is
	   small enough	so that	the grid intersects the	model, the model will
	   appear sliced, that is, only	the portion of the model beyond	the
	   grid	will be	visible.

       -G"n cflag gflag	vsize"
	   Configure the grid. If cflag	is set to zero,	n refers to the	grid
	   size. The grid is square, so	this number represents the number of
	   rays	(or cells) across the grid in both the X and Y directions.
	   However, if cflag is	set to non-zero, n refers to the cell size
	   (ray	separation) in millimeters. If gflag is	set to zero, the grid
	   origin will be aligned with respect to the model RPP, otherwise it
	   will	be aligned with	the model origin.  Vsize is a floating-point
	   number which	represents the view size. If it	is greater than	zero,
	   the field of	view will be set to take in an object of that size.
	   Otherwise, the view size will be set	relative to the	model RPP. The
	   grid	size and cell size are related;	when perspective is set	to
	   zero	(see the -p option), grid size times cell size equals view
	   size. When perspective is non-zero, the grid	and eye	distance are
	   also	involved, so the relationship is less pertinent. The defaults
	   for this command are; G 32 0	0 0.0, which means grid	size of	32,
	   centered WRT	the model RPP and view size set	relative to the	model

	   Set noise threshold for the Infrared	(IR) Module to n.

	   Read	and display infrared data from file.

	   Set hidden-line flag	to n. When set to non-zero, this causes	a
	   hidden-line drawing to be produced rather than the usual shaded
	   color image.	If n is	set to 1, the drawing will be black-on-white,
	   and if set to 2, white lines	will be	drawn on a black background.
	   The default is to disable this feature.

	   Set maximum number of bounces (levels of recursion) in ray tracing.
	   For instance, it requires one bounce	to get the first reflection
	   off of a mirrored surface, and several to get through a transparent
	   object. If no transparent objects or	mirrors	are modeled, it	is
	   more	efficient to leave this	at the default of zero,	but, if	such
	   objects are modeled,	it is best to be safe and use at least 6
	   bounces, better yet a dozen or so since multiple mirrors or
	   critical angles encountered in refraction can lead to many bounces
	   for a given ray.

	   Input key-frame from	file. This command reads a saved view as
	   output by mged(1) when using	the savekey command. When using
	   savekey the user must be sure not to	specify	the time field,
	   otherwise he	must remove the	resultant lines	from the output	file
	   either manually or as a side-effect of running an interpolation
	   program. If these time stamps remain	in the file, lgt will likely
	   get sick as the input gets out of phase. Specifying this command
	   without a file argument will	disable	key-frame input.

	   Set number of processors to use for ray tracing to n. This
	   parameter is	only meaningful	when running in	a parallel processing
	   environment.	The default is set, in a host-dependent	manner,	to the
	   maximum number of processors	available in a parallel	configuration.

	   Write image output in file or display on device. By default the
	   output is displayed on a frame buffer. The default frame buffer is
	   configured by the frame buffer library (see libfb(3B)), based on
	   available graphics devices. The default may be overridden more
	   generally with the environment variable

	   FB_FILE (see	brlcad(1)).

	   Write errors	to file	rather than the	terminal. The default is to
	   write to the	standard output	in a scrolling window (sub-section of
	   the terminal	screen), if the	standard input is attached to the
	   terminal; or	to standard error, if input has	been redirected.

	   Set the relative perspective	to n. When this	number is positive,
	   the relative	distance of the	grid and the observer from the model
	   centroid (or	origin)	will be	adjusted automatically to yield	the
	   specified ray divergence factor (rays emanating from	a point, the
	   observer position, to the respective	grid cells). When set to zero,
	   there is no perspective (parallel rays). Perspective	increases in
	   direct proportion to	this number; the default is 0.25. When n is
	   negative, perspective is governed by	the position of	the observer
	   (eye) and the grid, and by the view size.

	   If n	is non-zero, enter the Infrared	Module.

	   Read	light source data base from file.

	   Read	material data base from	file.

       -x"a b"
	   Set the starting and	ending pixel to	a and b. This sets up left and
	   right boundaries within the grid to limit the ray trace to a
	   rectangular sub-grid.

	   Set the overlap reporting flag to n.	When set to non-zero, this
	   causes overlaps to be reported to the log file or terminal (see the
	   -O option). The default is to report	overlaps.

       -y"a b"
	   Set the starting and	ending scan line to a and b in the sub-grid.

	   Set shadow computation to n.	When set to zero, no shadows will be
	   computed. This is useful when computing a view from inside the

       Required	arguments to the program are model.g which is the name of the
       mged(1) data base, followed by one or more objects which	are names of
       regions or groups in the	geometry hierarchy which are to	be rendered.
       Commands	are read from the standard input, whether in batch mode	or
       interactive. In general,	all command-line options can be	invoked	as
       commands, by using the identical	option letter, but there are a few
       commands	that are not available as command-line options.

   Commands (not available as options)
       Arguments that appear in	brackets are optional. In general, when	an
       optional	file argument is left out, the user will be prompted; and if a
       flag is omitted,	the state will be toggled (unless otherwise specified

	   Print the menu of available commands.

       ! [command [arg...]]
	   Execute command from	the shell. If the environment variable $SHELL
	   is set, it will be executed,	otherwise /bin/sh is the default
	   shell. If a command is specified, the shell will be fed it as input
	   (along with any arguments), otherwise, an interactive shell is

       . [flag]
	   Set buffered	pixel I/O to flag. The values for specifying the
	   buffering scheme are	as follows:

	   Programmed I/O. Each	pixel is output	immediately after it is

	   Paged I/O. This is generally	the most efficient I/O scheme, but
	   only	updates	the image as it	crosses	a page boundary. Page sizes
	   vary	with the graphics device and host, but range from 8 to 42 scan

	   Scan	line I/O. Each row of pixels is	output when ready.

       In the absence of flag, the state is cyclically incremented.

       # [comment]
	   This	is the comment command,	useful for preparing input files. The
	   entire line is copied to the	log file or terminal (see the -O

	   Submit a batch run. The current parameters are used to build	a
	   script in a temporary file, and this	is submitted to	the batch
	   queue (see batch(1)), subject to MDQS availability. The user	will
	   be sent mail	when the job is	finished.

	   Enter cursor	input module. The user can manipulate the cursor to
	   specify rectangular portions	of the screen or specific pixels to
	   ray trace. This module has a	help facility, accessible by typing a

	   When	using the Silicon Graphics IRIS	in local mode, the user	can
	   use the mouse to position the cursor	and sweep out rectangular
	   areas. These	operations require the user to press the middle	mouse
	   button to control sweeping operations and the selection of
	   positions. The cursor module	implementation on the IRIS also	has a
	   window-in and window-out command which allows the user to specify a
	   translation and scaling of the grid to include a smaller or larger,
	   respectively, area of the model to ray trace.

	   Erase frame buffer. Fill grid area of frame buffer with black.

	   Animate on-screen movie. This command is currently only implemented
	   on the IRIS,	and displays movies such as those generated with this
	   program (see	the J command).

       H [file]
	   Save	frame buffer image. Stores the image on	the current frame
	   buffer in file. This	can also be used to transfer the image to
	   another graphics device.

       h [file]
	   Restore a saved image from file. Reads the image from the specified
	   file	or device and displays it on the current frame buffer.

	   Make	a movie. This command prompts for information necessary	to set
	   up a	movie. Both full-screen	and postage-stamp movies are
	   supported. In specifying the	number and size	of frames to shoot for
	   a postage-stamp movie, the user is limited by the graphics device's
	   display memory (the entire movie must fit in	the frame buffer).
	   Full-screen movies are saved	on the disk, 1 frame per file, so they
	   can be any displayable size given you have the disk space.

       L id
	   Modify light	source data base entry id. The user will be prompted
	   for information necessary to	position and describe the light
	   source. Light source	zero has special significance and a dual
	   purpose. It simulates an ambient light source and, its position
	   specifies the position of the observer (the eye). Note that only
	   the program's (in-core) copy	of the data base is modified until
	   another command (see	the V command) is used to write	it to a	file.

       l id
	   Print light source data base	entry id. Display the current copy of
	   the specified entry on the terminal's screen. If no entry is
	   specified, all entries will be displayed.

       M id
	   Modify the material data base entry id. The user will be prompted
	   for information necessary to	describe the properties	of the
	   material necessary for the lighting model calculations. As with the
	   light source	data base, a separate command (see the W command) is
	   used	to save	the current modifications in a file.

       m id
	   Print material data base entry id. Display the current copy of the
	   specified entry. The	id should match	the material id	in the mged(1)
	   data	base. If no entry is specified,	all entries will be displayed.

       N [temperature]
	   Specify temperature for IR painting.

	   Print mged(1) regions and associated	IR temperature mappings.

	   Assign IR temperature to mged(1) region or group.

       q or ^D
	   Quit. Normal	exit from the program.

	   Ray trace current view. Initiate a run. During a batch mode run,
	   this	command	will be	given automatically on encountering an
	   end-of-file if it hasn't been given explicitly. Note	that if	an
	   explicit quit command is given, an end-of-file condition will not
	   be encountered.

	   Redraw the terminal screen.

       S [file]
	   Save	an executable script in	file. Writes out a Bourne shell	script
	   which will restart the program with the current set of options.
	   Note	that the user should also use the commands (see	below) to save
	   the light source and	material data bases before quitting.

       T [fbsize]
	   Specify the frame buffer size as fbsize. On windowing systems, a
	   frame buffer	window will, by	default, be opened which just fits the
	   image. This command allows one to specify a larger window. If the
	   window is a multiple	of the image size, zooming will	be used	to
	   enlarge the image to	fit the	window.	It is desirable	to specify an
	   exact multiple, so that the image will fill the window. On graphics
	   hardware that does not have a windowed environment, there may be
	   only	fixed window sizes such	as 512 and 1024, in which case,	you
	   will	get the	best match. Specifying zero for	fbsize will restore
	   the default behavior.

       U [file]
	   Save	IR data	base in	file.

       u [file]
	   Read	IR data	base from file.

       V [file]
	   Save	light source data base in file.

       W [file]
	   Save	material data base in file.

	   Display pseudo-color	IR mapping scale.

       This program is designed	to be used in two modes; interactively for
       setting up parameters, and in batch mode	for rendering high-resolution
       images. First, the user should invoke the program in the	interactive
       mode without options. While in this mode, the user should set up
       parameters for a	low resolution ray trace, perhaps by using the default
       resolution (32x32 grid),	ray trace that view, tweak parameters as
       necessary, and iterate. As the user converges on	the acceptable
       combination of parameters, there	is a command which will	save a UNIX
       shell script. This command generates a shell script that	will invoke
       the program with	the current set	of parameters, data bases, objects,
       etc. When everything is to the user's liking, he	or she should increase
       the resolution, change the output device	to a file name so as not to
       tie up a	graphics device, make sure that	the error output is being
       re-directed to a	file as	well, and that all changes to the material or
       light data bases	have been written out. Finally,	the user can either
       spawn a batch run with a	command, or use	the above mentioned command to
       save a shell script and either quit or proceed to set up	another	view.
       The command to create a batch run actually executes the batch(1)
       command (subject	to MDQS	availability), with the	current	set of
       parameters, etc.	As an alternative to generating	a batch	run from the
       program,	the script files can be	fed by hand to the batch(1) command or
       can just	be detached as background jobs (see EXAMPLES for the proper
       method) with their input	redirected from	a file or /dev/null.  If the
       program is detached without re-directing	its input, the full-screen
       display will be generated which will tie	up that	terminal or layer (in
       a windowed environment).	If the program is running in batch mode, and
       it detects an end-of-file before	the command is given to	generate an
       image, it will generate one automatically.

       The following command will start	up an interactive session which	will
       use the Silicon Graphics	IRIS's default frame buffer device (/dev/sgi)
       on a host address to display the hull and turret
       of the target description in file tank.g.

	   $ lgt -o tank.g hull turret

       This command will start up an interactive session on an alternate
       device on a remote host and will	begin at the 251st scan	line and
       complete	a 512x512 image	(handy in the event that the computer goes
       down in the middle of ray tracing an image). Note that since the	-y and
       -G options take multiple	arguments, they	must appear in double-quotes.

	   $ lgt -G "512 0 0 0.0" -o -y	"250 511" tank.g hull turret

       This will run the program as a detached process by executing a saved
       script called tankscript.

	   $ tankscript	_ /dev/null _

       The "lgt" Lighting Model, mged(1), pix-fb(1), librt(3), libfb(3)

       Gary S. Moss

       This software is	Copyright (c) 1987-2013	by the United States
       Government as represented by U.S. Army Research Laboratory.

       Reports of bugs or problems should be submitted via electronic mail to

BRL-CAD				  07/08/2017				LGT(1)


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