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Channel to grid
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(Display only) The select channel to be gridded.
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Output grid
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(Display only) The selected output grid.
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Grid cell size
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(Display only) The grid cell size.
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Xmin, Ymin,
Xmax, Ymax
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X and Y minimum and maximum coordinates. Leaving this entry blank, produces a grid covering the entire dataset. To grid a subset for the data, enter the limits of the bounding rectangle.To default any of these parameters, you must honour their position along the entry by providing the separating commas. Entering a range of ,0,0,0 will cause the grid to cover the maximum limits of the data plus the blanking distance.
If no value is entered for the blanking distance, the grid will cover the maximum limits of the data plus eight times the grid cell size.
Script Parameter: RANGRID.XY
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Log option
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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
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Log minimum
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If gridding in log space (see the Log options above), this parameter specifies the minimum value. The default is 1.
Script Parameter: RANGRID.LOGMIN
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Low-pass desampling factor
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The de-sampling factor as a multiple of the grid cell. This factor effectively acts as a low-pass filter by averaging all points into the nearest cell defined by this factor.
For example, a factor of 3 would first average database points into a coarse grid whose cells size is 3 times the final cell size. The default is 1, producing no pre-filtering other than de-aliasing by averaging points within a cell. If the resulting grid is too noisy around data points, increase the desampling factor.
Script Parameter: RANGRID.DSF
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Blanking distance
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All grid cells farther than the blanking distance from a valid point will be set to dummies in the output grid. The default 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
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Tolerance
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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
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% pass tolerance
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The required percentage of points that must pass the tolerance. The default is 99%.
For a more accurate grid, increase the percentage.
Script Parameter: RANGRID.PASTOL
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Maximum iterations
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Iterations at the finest coarseness level will stop when the maximum number or iterations is reached (default is 100). 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
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Starting coarse grid
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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
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Starting search radius
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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
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Internal tension (0-1)
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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.TENS
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Cells to extend beyond data
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This is the number of grid cells to extend beyond the outside limits of the data. The default is the integer value of blanking distance/grid cell size.
If the X and Y range values are not defined, the grid size will be set to the actual data range plus this value.
This parameter is commonly used in conjunction with the blanking distance parameter. For best results, use the blanking distance parameter to control the amount of coverage around data and this parameter to set the default grid size – with this distance generally being smaller than the blanking distance to provide clipping around the grid.
Do not use this parameter in place of the blanking distance in order to fill interior regions of the grid, as results are generally poorer than using the blanking distance. This is because the blanking distance measures the true radial distance between a given location and the nearest data point while the "cells to extend" is measured only in X or in Y. The blanking distance is a true distance and the "cells to extend" is the number of cells, so you must multiply by the actual cell size to compare the two.
Script Parameter: RANGRID.EDGCLP
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Weighting power
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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
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Weighting slope
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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.
To grid nonisotropic data, set the weighting slope > 1. For instance, in aeromagnetic survey data with line spacing 200 metres apart and readings every 5 metres along the line, the 50 metre cell size block will include a large number of real data points to be combined into one weighted location and z value; in such case, setting the weighting slope to 5.0 will produce a smoother non-aliased outcome relative to a setting of 0.0.
Script Parameter: RANGRID.WTSLP
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Prior to gridding the data for the 2 log-linear options the data is altered as follows:
The illustration below intends to convey the variation between the various log options.
