⬡ Stereonet
Cur---/-- │ DD---/-- │ View000/90
☰ Data
n = 0
▤ Statistics
Load data to view.
◉ Stereogram
Sep
>_ Console
> 
⬡ Stereonet ☰ Data ▤ Stats >_ Console n=0 κ=-- cur ---/-- OS² v1.0
DATA
PROC
ERR
EXP
BEARING SYSTEMS
BS-7700 STEREONET TERMINAL — S/N: 0042-1977
Proj
Net
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Inv Y
MANUAL
PROJECTS
REFS

The Structural
Geologist's
Companion

A BEARING SYSTEMS Publication
ISSUE #1 — STEREONETS FOREVER
FREE / PRICELESS
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APPROVED
LOWER HEMISPHERE ONLY PEER REVIEWED*
*by Gauss, the family's westie
What Is A Stereonet?
IMPORTANT

A stereonet is a lower-hemisphere stereographic projection — a way to flatten a hemisphere onto a flat circle so you can plot and analyse 3D orientations on a flat surface.

Think: squashing a salad bowl flat, mathematically.

Imagine looking straight down into a bowl. Every plane slicing through the bowl traces an arc (great circle), and the perpendicular to that plane pierces the bowl at a single point (pole).

← great circles
   are arcs

Two projections exist:

Equal-Area
(Schmidt / Lambert)
Preserves density.
Use for statistics.
THIS IS DEFAULT
Equal-Angle
(Wulff / Stereographic)
Preserves angles.
Use for constructions.
NICHE USE
Notation Guide
MEMORIZE

Planes are described by two angles:

Dip Direction / Dip 120/45 → dips 45° toward azimuth 120° Strike / Dip (Right-Hand Rule) 030/45 → strike N30°E, dip 45° to the right (dip direction = strike + 90° = 120°)
RIGHT-HAND RULE!

Lines (fold axes, lineations, etc.):

Trend / Plunge 120/45 → plunges 45° toward azimuth 120°

Quadrant notation is also supported:

N45E → 45° S30W → 210° N0 → 0° S30E → 150°
NB: Clar compass users: your readings are already in dip-direction format. Alles Clar?
Reading The Plots
ESSENTIAL

Poles (dots): Each dot = one plane's orientation. A cluster of poles = a set of similarly oriented planes. A girdle of poles = folded rocks.

Great circles (arcs): The trace of the plane itself. Vertical planes pass through the center. Horizontal planes plot as the outer circle.

Contours: Density in Multiples of Uniform Density (MUD).

MUD = 1 → random background level MUD = 3 → 3× random expectation MUD = 6 → strong preferred orientation MUD = 10 → VERY strong
MUD > 3 = REAL SIGNAL

Mean direction (large dot): The Fisher mean of all poles. The confidence cone (dashed circle) shows the 95% uncertainty region.

Eigenvectors (V1, V2, V3): Principal directions of the distribution. V1 = maximum concentration, V3 = minimum. For a girdle, V3 is the fold axis.

Fisher Statistics
FOR CLUSTERS

The Fisher distribution is the spherical equivalent of the normal distribution. Use it when your data forms a single cluster.

κ (kappa) — Concentration parameter κ > 50 very tight cluster κ ~ 20 moderate cluster κ ~ 5 dispersed κ < 2 nearly random α₅₅ — 95% confidence cone The mean lies within this cone with 95% probability. α95 < 5° = excellent α95 ~ 10° = decent α95 > 20° = don't publish this ← SIC R̄ (Rbar) — Mean resultant length Range: 0 (chaos) to 1 (perfection) R̄ > 0.9 = well clustered
κ > 20 = PUBLISHABLE MAYBE
Fabric Analysis

Woodcock Parameters (shape + strength):

K = ln(S1/S2) / ln(S2/S3) K > 1 → cluster (bedding) K < 1 → girdle (fold) K = 1 → transitional C = ln(S1/S3) C ≈ 0 → random C > 3 → strong fabric C > 5 → VERY strong
WOODCOCK (1977) — SEMINAL PAPER

Vollmer Triangle (P + G + R = 1):

P = S1 - S2 (point/cluster) G = 2(S2 - S3) (girdle) R = 3 · S3 (random) P = 1 /\ / \ Ternary plot. / • \ Your data / \ goes here. /________\ G = 1 R = 1
EIGENVALUES FTW

Bingham Parameters: κ₁ and κ₂ describe the concentration along V2 and V3 (both ≤ 0). More negative = more concentrated.

Console Reference
RTFM

The OS² console accepts the following commands:

help — show available commands plot — parse & plot data from Data window clear — clear all plotted data stats — print statistics to console contour — toggle density contours export — download stereonet as SVG rotate <t> <p> — set view center reset — reset to standard view sample — load sample dataset tile — retile windows to fit screen add <dd> <dip> [flags] — add measurement color [n] [#hex] — view/set palette rem <text> — add comment to data new — clear & start fresh save <name> — save current project load [name|#] — load a saved project projects — list saved projects spin <a> <p> <s> [tps] — animate rotation spin off — stop animation groups — list data groups group <n|name|all> — select stats group stereogram [dm] — 3D stereogram / debug cls — clear console output about — about this software

Extended data format:

dipdir dip [p|l] [g] [#RRGGBB] p / l — override type (plane/line) g — plot great circle #RRGGBB — custom color Data groups: g Bedding #4ac8ff p 120 45 g Foliation #ff5577 p off 045 60 Tokens: name, #color, p/l, off

Hotkeys (when no input focused):

1–8 — select palette color c — toggle contours g — toggle great circles e — export SVG r — reset view p / l — set type planes/lines ↑↓←→ — nudge rotation (5°)

Mouse & global:

• Ctrl+click — add plane at cursor.
• Ctrl+Shift+click — add line at cursor.
• Ctrl+Z — undo last added point.
• Ctrl+/ — focus console.
• Ctrl+S — save project.
• Drag stereonet to rotate view.
• Right-click palette swatch to pick color.
• Last saved project auto-loads on startup.

POWER USER MODE
Classifieds

CLAR Compass Co.

“Alles Clar?”

The Original Geological Compass — Trusted Since 1954

Now in limited edition anodised titanium. Ask your local dealer. Not responsible for lost bearing in the field.

FIELD BOOTS UNLIMITED

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Now with 40% more ankle support. Available in Outcrop Brown and Flysch Grey.

SCHMIDT GRAPH PAPER

Premium Equal-Area Nets — 100 Sheets
Now obsolete. Use bearing.js instead. We don't know why we still sell these.
SALE
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Letters to the Editor
Dear Editor, I've been using stereographic projection for 30 years and I STILL don't understand why some people use equal-angle projection for statistical work. What is WRONG with these people?
— Prof. Dr. H.-W. Müller, Göttingen
Ed.: We agree, Herr Professor. We agree.
Dear Editor, Please stop calling it a “Schmidt net”. Lambert had it first.
— A. Lambert (no relation), Strasbourg
Dear Editor, Your software crashed during my thesis defense. The committee was not impressed. I blame the contour algorithm.
— Anonymous PhD Candidate, Somewhere in Bavaria
Dear Editor, I tried to explain to my spouse what I do for a living using your stereonet software. They now think I'm some sort of abstract artist. I got a gallery showing. Thank you?
— Dr. R. Tectonic, Department of Confused Disciplines, ETH Zürich
KEEP THE LETTERS COMING
References
CITE YOUR SOURCES
Fisher, R.A. (1953) Dispersion on a sphere. Proc. R. Soc. Lond. A, 217, 295–305. Woodcock, N.H. (1977) Specification of fabric shapes using an eigenvalue method. Geol. Soc. Am. Bull., 88, 1231–1236. Tocher, F.E. (1979) The computer contouring of fabric diagrams. Comput. Geosci., 5, 73–126. ← SAMPLE DATA Vollmer, F.W. (1990) An application of eigenvalue methods to structural domain analysis. Geol. Soc. Am. Bull., 102, 786–791. Bingham, C. (1974) An antipodally symmetric distribution on the sphere. Ann. Stat., 2, 1201–1225. Kamb, W.B. (1959) Ice petrofabric observations from Blue Glacier, Washington. J. Geophys. Res., 64, 1891–1909.
WE READ THE PAPERS SO YOU DON'T HAVE TO
About / Credits

bearing.js — Structural geology stereonet library in pure JavaScript. No dependencies. Open source. Dangerously functional.

Implements: equal-area & equal-angle projection, Fisher statistics, principal axis analysis (orientation tensor, eigendecomposition), Woodcock & Vollmer fabric parameters, Bingham distribution, kernel-density contouring, attitude I/O (dip-direction, strike, quadrant notation).

Sample data: 200 poles from Tocher (1979).

Made with equal parts science and stubbornness by the Geoscientifical Chaos Union.

GCU

“Serious science. Questionable aesthetics.”

Issue #2 coming... eventually.
Printed on recycled field notebooks.
Built with bearing.js and a generous amount of AI assistance.

BEARING SYSTEMS — BS-7700 — MADE ON EARTH
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References
Schmidt, W. (1925)
Gefügestatistik
Mineralogische und Petrographische Mitteilungen, 38, 392–423.
Fisher, R.A. (1953)
Dispersion on a Sphere
Proceedings of the Royal Society of London A, 217, 295–305.
doi:10.1098/rspa.1953.0064
Kamb, W.B. (1959)
Ice Petrofabric Observations from Blue Glacier, Washington
Journal of Geophysical Research, 64, 1891–1909.
doi:10.1029/JZ064i011p01891
Bingham, C. (1974)
An Antipodally Symmetric Distribution on the Sphere
Annals of Statistics, 2, 1201–1225.
doi:10.1214/aos/1176342874
Woodcock, N.H. (1977)
Specification of Fabric Shapes Using an Eigenvalue Method
Geological Society of America Bulletin, 88, 1231–1236.
Tocher, F.E. (1979)
The Computer Contouring of Fabric Diagrams
Computers & Geosciences, 5, 73–126.
doi:10.1016/0098-3004(79)90019-0
Vollmer, F.W. (1990)
An Application of Eigenvalue Methods to Structural Domain Analysis
Geological Society of America Bulletin, 102, 786–791.
Campanha, G.A.C.; Carneiro, C.D.R.; Pereira, G.G.A.; Furumoto, S.; Hasui, Y.; Nagata, N. (1996)
Uso do Programa Trade Para Determinação de Direções Principais de Esforços Pelos Métodos de Arthaud e Angelier
In: Carneiro, C.D.R. (Org.). Projeção estereográfica para análise de estruturas. São Paulo: UNICAMP/CPRM/IPT.
Yamamoto, J.K.; Souza, G.A.J.K.; Campanha, G.A.C. (1996)
Trade — Programa Para Tratamento de Dados Estruturais
Software. São Paulo: UNICAMP/CPRM/IPT.
Grohmann, C.H. & Campanha, G.A.C. (2010)
OpenStereo: Open Source, Cross-Platform Software for Structural Geology Analysis
AGU Fall Meeting Abstracts, IN31C-06, San Francisco, CA.
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