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The line

The ways to notice the line:

• 3-part version - (45/30 NE or 225/30 NE - the two possibilities of describing the same line). Write: the plunge direction (value:0-360), plunge (0-90) and approximate plunge direction (N, NW...).
• 2-part version, british - (30-045) frequently used,because it's more useful, write: plunge(0-90) and plunge direction(0-360).

For example we choose a line: 45/30 NE, 225/30 NE or 30-045. In the first way we have two possible plunge direction in this example it's NE and opposite SW. The british version is more useful because giving the plunge direction eliminates needs of giving an approximate plunge direction. Only need to write the plunge direction 45, and we know that its plunge at NE.

Stereografic projection of the line

The line is placed at the center of the hemisphere. Now the length of the line is increased until the line meets the hemisphere's surface. The spherical projection of the line is the point where the line and hemisphere meet.

The two particular case of the line is the vertical and horizontal line.

The vertical line is always the point at the center of stereogram, horizontal line is two points at the opposite sites of the primitive circle.

To produce projection of a line:

from british notice - The procedure is explained with the aid of an example.
Draw the stereogram of the line: 30-045.
On the overlay mark point to represent the strike 45. Rotate the overlay until point joins the equator. Then measure out the plunge angle 30 inwards, along the equator towards the center of underlying net. Finally, establish a point which is the required line.

from the 3-part notation - Again we use example for explanation: the line 225/30/NE.
On the primitive circle mark point to represent the strike 225. Rotate the underlying net to join the point with equator. Then on the overlay find the plung at NE and along the equator measure 30 degrees, inwards from the primitive circle. It's the same line as in the first example but the notation differs.

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Autor: Kamil Wojtanowski[Contact]