Select a channel from the database to be gridded.

Script Parameter: E3MGRGRD.CHAN

The output grid will be placed in this file. The type of file can be controlled using the Browse tool, which is accessible from the list button.

Script Parameter: E3MGRGRD.GRDNAME

Specify the grid cell size. This should normally be ¼ to ½ the nominal data sample interval. If not specified, the data points are assumed to be evenly distributed and the default cell size will be set to:

Script Parameter: E3MGRGRD.CS

Display grid in a new map, the current map, or choose not to display the new grid.

Script Parameter: E3MGRGRD.NEW (0:Current, 1: New, -1 Do not display)

(Display only) The select channel to be gridded.

(Display only) The selected output grid.

Specify the grid cell size. The grid cell size is in the distance units of the data. We recommend a cell size of ¼ to ½ the nominal data sample interval. The default is one quarter the average data separation based on a statistical average. A smaller cell size may be required if the data is to be contoured (we recommend 2 mm. or 1/10 inch at plot scale for contouring). This can be achieved by specifying a smaller cell size and larger desampling factor (desamp), or by regridding the grid using BIGRID.

Script Parameter: E3MGRGRD.CS

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, then the grid will cover the maximum limits of the data plus 8 times the grid cell size.

Script Parameter: E3MGRGRD.XY

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: E3MGRGRD.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: E3MGRGRD.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: E3MGRGRD.TOL

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

Script Parameter: E3MGRGRD.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: E3MGRGRD.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: E3MGRGRD.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: E3MGRGRD.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: E3MGRGRD.TENS

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: E3MGRGRD.EDGCLP