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Transcript
```Stereonets
Solving geometerical problems – displays geometry and orientation os lines
and planes.
It is a three-dimensional protractor.
With a normal protractor, we can plot trend of lines, measure angles between
lines, construct normal e.g., perpendicular lines) line, and rotate lines by
specified angles.
Stereonet projection allows us to do the same manipulations but in 3dimensions. We can plot the orientation of planes, determine the
intersection of two planes, angles between planes, rotate lines and
planes in space about vertical, horizontal and inclined axes.
Stereonets
Solving geometeric problems –
displays geometry and
orientation of lines and planes.
 A line is represented as
passing through the center of a
reference sphere and
intersecting its lower
hemisphere.
 Flatten the sphere to two
dimensions by projecting the
lower hemisphere intersections
to an equatorial plane of
reference that passes through
the center of the sphere.
 Lower hemisphere
intersections are projected as
rays upwards through the
horizontal reference plane to the
zenith of the sphere.
Where rays of projection pass
through the horizon reference
plane, point or great circle
intersections are produced.
These are stereographic
projections of planes or lines.
Stereonets
Lines and Planes
What is a line?
The locus of points that define a line.
We can measure the orientation of a plane or a line. Its orientation in space, it
is fundamental to describing structures. Lines are fold axis, slip vectors,
lineations, etc.
What is a plane?
Two lines determine a plane.
If we know the orientation of two lines, the orientation of the plane that contains
these two lines is also known.
Lines and Planes
Planes are bedding planes, fault planes, dikes.
Rules
If the orientations of two lines in a plane can be established, the orientation of
the plane is known.
Any two lines will work, lines do not need to be parallel or close to parallel.
Strike and dip are two lines, with these two measurements, we define the
plane.
For the special case of a horizontal plane, all lines are strike lines.
Strike and dip are measurements required to define the orientation of a plane.
Strike is the trend of a horizontal line in a plane. Its inclination is defined a
0°.
The dip of a plane, is the inclination of the line that defines the steepest
inclination in a plane.
Stereonet
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Stereonets

Steeply-plunging lines
stereographically project
to locations close to the
center of the horizontal
plane of projection.

Shallow-plunging lines
stereographically project
to locations near the
perimeter of the plane of
projection.
Stereonets

Steeply-plunging lines stereographically project to
locations close to the center of the horizontal plane of
projection.

Shallow-plunging lines stereographically project to
locations near the perimeter of the plane of projection.

Steeply-dipping planes stereographically project as great
circles that pass near the center of the plane of projection.

Shallow-dipping planes stereographically project as great
circles that pass close to the perimeter of the plane of
projection.
Stereonets
The distance that a great circle or point departs from the center
of the plane of projection is a measure of the degree of the
inclination of the plane or line.
The trend of the line connecting the end points of a great circle
corresponds to the strike of the plane.
Stereonets
Poles:
The orientation of a plane can be uniquely described by the
orientation of a line perpendicular to a plane.
If the trend and plunge of a normal (pole) to a plane is known,
the orientation of the plane is also known.
Go to overhead and class exercise
```
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