You can either grid the original data or its logarithmic (base 10) representation. Gridding the log of the data can be a very effective way to reduce distortion due to highly skewed data such as geochemical data.

The options are:

• linear: grid the data as it is.
• log, save as linear: grid the data in logarithmic space and clip all values less than ‘Log minimum’ to the ‘Log minimum’ value, then convert the data back to linear space before saving it to the grid file.
• log-linear, save as linear: grid the data above the positive ‘Log minimum’ and below the negative ‘Log minimum’ in logarithmic space (flip the sign of the data originally in the negative range to take the logarithm then inherit back the sign of the original data; grid the conditioned data). After gridding, all cell values outside the ± ‘Log minimum’ range are converted back to linear space and scaled to maintain continuity at the boundary. Data within the ± ‘Log minimum’ range remains intact and is gridded in a linear sense.
  Finally, the linear representation of the data (in both ranges) is saved to the grid file.
• log, save as log: same as ‘log, save as linear’ except that the grid values are kept in log space: the gridded values are saved to the grid file in their logarithmic representation.
• log-linear, save as log: same as ‘log-linear, save as linear’ except that the grid values are not converted back from log space. The output grid is in logarithmic space with the large amplitude anomalies being somewhat moderated.

Script Parameter: RANGRID.LOGOPT
  linear: 0
  log, save as linear: -1
  log-linear, save as linear: -2
  log, save as log: 1
  log-linear, save as log: 2

If gridding in log space (see the Log options above), this parameter specifies the minimum value. The default is 1.

Script Parameter: RANGRID.LOGMIN

The de-sampling factor is defined as a function of the grid cell size. Before any further calculations, all points within cells of dimension cell_size x desampling_factor are averaged into a single value and placed in the center of the cell.

The default desampling (desampling_factor) is set relative to the contributing points as:

Desampling has two impacts:

• Effectively it acts as a low-pass filter. The larger this parameter the smoother the output grid.

• Speeds up the variogram calculation when the input database is very large.

If the database contains less than 100000 contributing points, the default is set to 1, and the only pre-filtering consists of de-aliasing at the cell level.

The variogram calculation duration is a function of the square of the contributing points. Increasing this factor visibly cuts down the variogram calculation time while little impact is seen on the variogram curve.

Script Parameter: RANGRID.DSF

All grid cells farther than the blanking distance from a valid point will be set to dummies in the output grid.
The default blanking distance is calculated as:

Preferably this parameter should be set to just greater than the maximum distance through which interpolation is desired.

Script Parameter: RANGRID.BKD

Specify the tolerance required for each grid cell (absolute error, in grid data units). The default is 0.1% of the maximum range of the observed data.For a more accurate grid, decrease the tolerance value.

Script Parameter: RANGRID.TOL

The required percentage of points that must pass the tolerance. The default is 99%. For a more accurate grid, increase the percentage.

Increase this percentage for a more accurate grid.

Script Parameter: RANGRID.PASTOL

Iterations at the finest coarseness level will stop when the maximum number or iterations is reached. At each greater coarseness, the maximum iterations is reduced by 2.Increase this value if more iterations are required to produce a more accurate grid.

Script Parameter: RANGRID.ITRMAX

Choose 16, 8, 4, 2 or 1 to indicate the desired coarseness of the starting iteration level relative to the final grid cell size. By starting with a coarser grid, the algorithm is able to produce a reasonable result in under-sampled areas. As the coarseness decreases, the algorithm becomes more sensitive to local features. Only decrease the coarseness from 16 to reduce gridding time.

Script Parameter: RANGRID.ICGR

This is the maximum search radius to use for establishing the starting grid values for the coarse grid. The default is four times the coarse grid size defined by the ‘Starting coarse grid’. If no data is found within the maximum search radius, the mean of the data is used as the starting value. If the search radius is too small, the starting grid can be a poor approximation of the desired grid, resulting in excessive processing time. If too large, too much time will be consumed establishing the original coarse grid.

Script Parameter: RANGRID.SRD

The degree of internal tension (between 0 and 1). The default is no tension (0), which produces a true minimum curvature grid. Increasing tension can be used to prevent overshooting of valid data in sparse areas; however, curvature in the vicinity of real data will increase. In general, the more sparse areas are present in the data (with localized highs and lows), the higher the tension should be set.

Script Parameter: RANGRID.IT

Edge clipping parameter, the number of grid cells to extend beyond the outside limits of the data. The default (-1) is not to apply edge clipping to the blanking distanced grid. Use this parameter to ensure the grid does not extend too far beyond the actual data limits, which can occur when using a large blanking distance with widely spaced data.

Script Parameter: RANGRID.EDGCLP

The weighting power is used to generate the coarse starting grid. Values within a coarse cell are weighed by the inverse of their distance from the coarse grid nodes raised to this power.The two weighting settings, weighting power and weighting slope, can be used to reduce the high-frequency aliasing caused by gridding at too coarse an interval.

Script Parameter: RANGRID.IWT

The weighting can further be moderated through the use of a slope parameter. The overall weighting is established as:

Where:

• distance is in grid distance units
• power is applied to the distance
• slope is in cell units, default is 0.0, where the only influence on the weight is from the nearest data points to each grid node.

Script Parameter: RANGRID.WTSLP