TERRAIN(1)

NAME

terrain - generate a pseudo-terrain height field from procedural noise

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SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO
AUTHOR
COPYRIGHT
BUG REPORTS

SYNOPSIS

terrain [-w x_postings] [-n y_postings] [-s xy_postings]
        [-L lacunarity] [-H h_value] [-O octaves] [-S scale]
        [-V x_scale,y_scale,z_scale] [-D x_delta,y_delta,z_delta]
        [-o offset] [-f function] [-c] [-v] > file.dsp

The terrain program produces a pseudo-terrain height field from procedural noise, suitable for use with a BRL-CAD dsp (displacement map) primitive. A noise value is computed for each point of an x_postings by y_postings lattice and written to the standard output as unsigned 16-bit integers in network (big-endian) byte order. The default grid is 512 by 512 postings.

The character of the terrain is controlled by selecting a noise function with -f and by tuning the fractal noise parameters. The standard output must be redirected to a file; terrain refuses to write binary data to a terminal. The resulting file is in the same binary format produced by asc2dsp(1) and can be referenced directly by a dsp solid in MGED.

OPTIONS

-w x_postings

Number of grid points (postings) in the X dimension. Default is 512.

-n y_postings

Number of grid points (postings) in the Y dimension. Default is 512.

-s xy_postings

Set the number of postings in both X and Y to the same value, producing a square grid.

-L lacunarity

Scaling factor between successive octaves of noise. Practical values are non-integer numbers between roughly 1.7 and 4.0. Default is 2.1753974.

-H h_value

The fractal increment (H) in the noise equation, controlling how detail diminishes across octaves. Usually near 1.0, which is the default.

-O octaves

Number of octaves of noise to layer. Typical values are 2 through 8. Default is 7.

-S scale

Scale the noise uniformly in X, Y and Z by scale. Values below 1.0 make the noise pattern finer; values above 1.0 make it coarser. This sets all three components of the vector scale (see -V). Default is 1.0.

-V x_scale,y_scale,z_scale

Non-uniform scaling of the X, Y and Z dimensions in noise space. Default is 0.0125,0.0125,0.0125.

-D x_delta,y_delta,z_delta

Translation (offset) applied in noise space, useful for sampling a different region of the noise field. Default is 1000,1000,1000.

-o offset

Offset value used by the multi-fractal (m) and ridged (r) noise functions. Default is 1.0.

-f function

Select the noise function used to generate the field. One of:

f: Fractional Brownian motion (fBm). This is the default.
t: Turbulence.
T: Inverted turbulence: 1.0 - turb(pt).
m: Multi-fractal.
r: Ridged multi-fractal.
L: A lunar-like surface.
l: Terrain with detail concentrated on peaks and in valleys.

-c

Toggle the conversion of output from host to network byte order. By default conversion is on; this only has an effect on little-endian hosts.

-v

Toggle verbose/debug output, printing which noise function is running and clamping diagnostics to standard error.

EXAMPLES

Example 1. Generate a terrain and build a dsp solid

terrain -w 256 -n 256 -f r -O 8 -S 1.5 > hills.dsp
mged terrain.g <<'EOF'
in mountains.dsp dsp f hills.dsp 256 256 0 ad 1 100
EOF

A 256x256 ridged multi-fractal height field is written to hills.dsp, then imported as a dsp primitive 256 cells wide and tall, smoothed, with a cell width of 1 and a height multiplier of 100, yielding a ridgeline of mountains in the database terrain.g.

Example 2. Create a tileable, square fBm patch

terrain -s 512 -f f -O 5 -L 2.0 -D 0,0,0 > patch.dsp

A 512x512 fractional Brownian motion field generated with five octaves and a lacunarity of 2.0, sampled at the origin of noise space for a repeatable result.