This gridding method uses Inverse-Distance gridding, in which the value of each of the data points is weighted according to the inverse of its distance from the grid node being computed, taken to a user-selected power. The difference with the Directional Weighting scheme is that you can specify a trend direction and strength, and the program will vary the weighting exponent so that points along the trend influence the grid node more than closer points perpendicular to the trend.
Advantages: This method has the same advantages as the Inverse-Distance gridding AND permits you to introduce directional bias to the gridding procedure.
Disadvantages: Directional Weighting can apply directional trends even if there are none – be careful to check against your data.
- Bidirectional: Choose this option if the data trends bidirectionally, as with fractures. This means, for example, that if the trend is at 45 degrees from a control point, it is also at 225 degrees.
- Automatic: Select this option if you don't know the directionality of the data and want the program to use a fabric analysis technique to determine a bias direction and strength.
- Display Fabric Report: Check this box to see the results of the fabric analysis.
- Manual: Select this option if you wish to define the known directionality of the data.
- Bias Direction: Enter the preferred direction, from 0 (north) to 180 (south) for the known trend, either by typing the direction into the prompt or by using the up- or down-arrow. The program will extend the trend 180 degrees opposite of the single direction you declare.
- Bias Strength: Choose from Weak, Moderate, or Strong. In general, the lesser the strength, the wider the tolerance the program will use around the bias direction, and the weaker the weighting exponent for points outside the bias tolerance.
- For Weak bias strength:
Points in the bias direction +- 20 degrees are modeled using an exponent of 1.8,
Points in the bias direction +- 25 degrees are modeled using an exponent of 1.9,
All other points are modeled using an exponent of 2.0.
- For Moderate bias:
Points in the bias direction +-15 degrees are modeled using an exponent of 1.8,
Points in the bias direction +- 20 degrees are modeled using an exponent of 1.9,
All other points are modeled using an exponent of 2.1.
- For Strong bias:
Points in the bias direction +-10 degrees are modeled using an exponent of 1.8,
Points in the bias direction +- 15 degrees are modeled using an exponent of 1.9,
All other points are modeled using an exponent of 2.2.
- Other: Click here to enter your preferred strength. Type in a value from 0 to 1.0.
- Unidirectional: Choose this option if the data trends uni-directionally, as with flow systems.
- Bias Direction: Enter the preferred direction, from 0 to 360 for the known trend, either by typing the direction into the prompt or by using the up- or down-arrow. (Unlike the Bidirectional modeling, the program will not extend the trend 180 degrees opposite.)
- Bias Strength:
- Choose from Weak, Moderate, or Strong. See the extreme examples above.
- Other: Choose this to enter your own value.
- Custom: Choose this option if your data has multiple trends. This allows you to define more than one direction and weighting in a user-defined text file.
- Direction/Weight Table: Select the name of the Directional Weighting 2D Sector table that contains the listing of azimuth directions and their weighting factors.
- Default Exponent: Use this prompt to enter the weighting factor (e.g. exponent) to be used for any directions not defined by the Sector table.
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