Multi-trend Gridding Advanced Options (Multiple Channels)

Use the Multi-trend Gridding Advanced Options dialog (geogxnet.dll(Geosoft.GX.GridUtils.NSIGriddingAdvancedOptions;Run)*) to specify advanced Multi-trend gridding options. This gridding method should be used with the distance units in ground coordinates. If your data is in geographic coordinates, project it to ground coordinates prior to running multi-trend gridding.

Multi-trend Gridding Advanced Options

Blanking distance	All grid cells within this distance will be evaluated. All grid cells farther than the blanking distance from a valid point will be set to dummies in the output grid. If left empty, the blanking distance is set to 10 times the grid cell size. Script Parameter: NSI_GRIDDING.INTERP_DISTANCE
Maximum iterations	The maximum number of iterations after which the gridding process stops. Select a value between 0 and 100. By default, the number of maximum iterations is set to 50. Increase this value to produce a grid that honours the survey data more closely. Script Parameter: NSI_GRIDDING.MAX_ITER
Trending factor	The higher the trending factor, the smoother the lineaments will be. Select a value between 0 and 100. By default, the trending factor is set to 100. Trending factor will default to 0 if the entry is left blank. Script Parameter: NSI_GRIDDING.TRENDING_FACTOR
Theta	The increment in degrees (between 1 and 90) by which to rotate the trend direction, in order to have an adequate number of survey points within the search radius for calculating the grid value at the centre of the search circle. The trend direction is rotated in the CW (clockwise) direction. See the Application Notes below for more details. The default is set to 10. Script Parameter: NSI_GRIDDING.THETA
[Reset]	Click this button to restore the gridding parameters to their default values.

Application Notes

Theta

In Figure 1 below, the original trend direction, determined by the structure tensor, is shown as an orange line. If it does not intercept real data within the search radius, the angle is changed by Theta (red solid line), and the search for real data is attempted again.

It is recommended to set the angle relatively small but greater than 0° not to deviate from the trend direction determined by the structure. On the other hand, a very small angle may increase the number of iterations and make the gridding process slower.

Figure 1: The blue cells contain real data; the green cell is the cell being analyzed; the purple circle is the search radius distance variable.

Acknowledgment