c) Equal-area stereonets are used in structural geology because they present b ) The north pole of the stereonet is the upper point where all lines of longitude. Background information on the use of stereonets in structural analysis The above is an equal area stereonet projection showing great circles as arcuate lines. Page 1. mm. WIDTH. Blunt. TUT. HT. T itillinn.

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Computers now make this task much easier.

Along the common great circle containing the two poles count in degree increments half of the angle found in D above. The stereographic projection gives an alternative parametrization of the unit circle:.

Also, there are many ways to rewrite these formulas using trigonometric identities. Instead, it is common to use graph paper designed specifically for the syereonet.

This space is difficult stereonwt visualize, because it cannot be embedded in three-dimensional space. All strike angles are measured with respect to the true North. Then measure the angle between them by counting grid lines along that meridian.

## Stereographic projection for structural analysis

When sterreonet projection is centered at the Earth’s north or south pole, it has additional desirable properties: There are different methods by which the points of intersection with the lower hemisphere are projected onto the stereonet.

Primitive circle is also a great circle but, it contains N, E, S and W directions at, and degrees intervals. However, stereographic fisheye lenses are typically more expensive to manufacture. Those labeled with dip amounts on the left side, dip to the west.

### Stereographic projection – Wikipedia

However, the equal area steronets will reduce the area distortion. It is the true North which is denoted by the azimuthal angle of degrees on the primitive. In electron diffractionKikuchi euqal pairs appear as bands decorating the intersection between lattice plane traces and the Ewald sphere thus providing experimental access to a crystal’s stereographic projection.

The plunge direction is evident as the quadrant your associated periphery point lies in and the angle along the hemisphere periphery from underlying N to the periphery point is your trend.

### Lab 5: Structural Analysis using stereonets

As in crystallography, planes are typically plotted by their poles. This orthogonality property is a consequence of the angle-preserving property of the stereoscopic projection.

That is the angle desired. Small circles run left-right latitudinal on the stereonets and are perpendicular to the great circles. General perspective Gnomonic Orthographic Stereographic.

This will help you learn the fundamentals of stereographic projection. H Determining the strike and dip of the common plane those two lines define.

Where it is defined, the mapping is smooth and bijective. Typically university geology and engineering students are expected create stereonets by hand.

## Stereographic projection

Under this reparametrization, the length element dx of the unit circle goes over to. Stereoneh geometrythe stereographic projection is a particular mapping function that projects a sphere onto a plane. Not all projections that preserve the orthogonality of parallels and meridians are angle-preserving. Circles on the sphere arew do pass through the point of projection are projected to straight lines on the plane.

You will need the following materials in order to proceed with this and the subsequent stereonet exercises: Wikimedia Commons has media related to Stereographic projection.

Parallel projection Orthographic projection Multiview projection Axonometric projection Isometric projection Oblique projection Perspective projection Curvilinear perspective Reverse perspective.

Most figures are made using an equal area projection, but sometimes and equal angle projection is used as well. The point you arrive represents a line perpendicular to the plane you started with, i.

For someone who is starting in geology or structural geology, it is highly recommended to use paper and pencil over software.

If it is less than 90 degrees it is the acute angle, otherwise it is the obtuse angle.

Similarly, a fault plane is a planar feature that may contain linear features such as slickensides. The popularity of using stereographic projections to map panoramas over other azimuthal projections is attributed to the shape preservation that results from the conformality of the steronet.

Differential geometry and applications. All lines in the plane, when transformed to circles on the sphere by the inverse of stereographic projection, meet at the projection point. Mathematical Analysis 2 ed.

Fraundorf, Wentao Qin, P.