Equal Angle projection preserves the geometry of projected shapes. The area on the surface of the sphere, represented by a projected region, depends on its location. The projected area of a given circle increases towards the equator of the projection see below for illustration. Equal Area projection distorts geometrical shapes such as small circles circles with centers not coincident with that of the sphere.
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The stereonet or stereographic projection is the most important visualization tool for orientation data in structural geology. Most figures are made using an equal area projection, but sometimes and equal angle projection is used as well. In most cases it is preferable to use a projection that optimises equal area, because it makes it easier to assess the spatial distribution of structures.
The projection that is usually chosen for this, is the Lambert Azimuthal Equal-Area Projection with equatorial aspect See: Snyder , p.
In geology this is usually referred to a Schmidt Net , after Walter Schmidt. Angles are slightly distorted and make the circles appear as ellipses. The x-axis horizontal and y-axis vertical coordinates of a latitude-longitude measurement can be calculated using the following formula:.
Equal angle projection preserve angle but severely distort areas. The projection used for this kind of plots is the Stereographic Projection with equatorial aspect See: Snyder , p. Equal angle projections preserve angles, which can be seen by all small circles being perfect circles. InnStereo latest. User interface 2. Stereonet 2. Projections 2.
Equal area projection 2. Equal angle projection 2. Further Reading 3. Layer types 4. Figure Formatting 5. Calculations 6. Views 7. Data Input and Output 8. Screenshots 9. Stereonet Edit on GitHub.
Background information on the use of stereonets in structural analysis. It is helpful to understand the 3-D geometry that is being represented on the 2-D stereonet projection plane. The diagrams below attempt to show you that geometry in three stages, each more complex. It may take some timeand focus to understand the geometry.
Stereonet Equal Angle / Equal Area Projection Comparison in Dips
The Schmidt net is a manual drafting method for the Lambert azimuthal equal-area projection using graph paper. It results in one lateral hemisphere of the Earth with the grid of parallels and meridians. The method is common in the geophysical sciences. In the figure, the area-preserving property of the projection can be seen by comparing a grid sector near the center of the net with one at the far right of the net. The two sectors have the same area on the sphere and the same area on the disk. The angle-distorting property can be seen by examining the grid lines; most of them do not intersect at right angles on the Schmidt net.