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Number of steps; means how many of variogram values will be calculated and step interval means the unit distance, from which the variogram will be calculated. Step tolerance means the distance that the step interval can be tolerated. Practically variograms are calculated up to half length of the size of the area to be considered. In horizontal calculations, step interval can be taken as the average distance between drills. In vertical, i.e. along the drills, calculations, step interval can be chosen a little bigger than the composite length. Step tolerance can usually be taken as the half of the step interval or a little bigger. Practical information given above relating to step interval, number and tolerance should be taken as analysis start values. In order to determine the optimal values relating to these parameters, it is required to consult a geostatistical expert. | |

Variogram is calculated in specified directions for anisotropical research and modelling. Direction and angles used in NETPRO/Mine is explained with 3-D ellipsoid shown in the figure below. 3D ellipsoid is described with six parameters: sizes of three main axis of the ellipsoid (r_{max}, r_{med }and r_{min}) and three angles that position the ellipsoid (α, β, and Q). Let's say there are three perpendicular axis on X, Y, Z cartesian coordinat system. The position of the ellipsoid is achieved with three sequential rotational movement. It is assumed that all angles are measured counter-clockwise. Main axis, middle axis and small axis of the ellipsoid are position on X, Y and Z direction, respectively before any rotational operation. | |

__First rotation around Z axis:__ Ellipsoid is firstly rotated with α angle around Z axis (This is called direction (azimuth) angle). Let's say X', Y' and Z' are rotated coordinate system. Please pay attention that Z' is equal to Z. Azimuth takes a value between 0 and 360. Azimuth is 0 in the reference direction taken as North.
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__Second rotation around Y axis:__Ellipsoid is then rotated with β angle around Y' axis (β angle is called **slope** (base)). Let's say X", Y" and Z" are the second rotated coordinate system. Please pay attention that Y" is equal to Y'.
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__Third rotation around X axis:__** **Lastly, ellipsoid is rotated with Q angle around X". Q is called **plunge** or **rake** angle. X''', Y''' and Z''' final coordinat system is achieved with this last rotation. Please pay attention that the X''' is equal to X'' in this system.
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Last rotation matrix is achieved by multiplying matrixes that represent the three rotation. The order, in which the rotations take place is important. Six parameters that describe the ellipsoid given in Netpro/Mine parameter files should be entered in the specified order: r max, r med, r min, α, β, and Q.
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Nugget Effect (Co): It is obtained from the variograms calculated during the best drills. Variograms that are modelled with different directions should have the same Co (nugget effect) value. Threshold Value (Sill) (c): It is the value of the variogram when it reaches the structural distance. Structural Range (Range) (a): It is the distance where variogram reaches delete value. | |