Regrid a Grid

Use the Grid and Image > Gridding > Regrid a Grid menu option (REGRID GX) to re-apply a gridding process to an existing grid. This can be done to change the cell size of a grid, or to apply filters along the grid lines.

Regrid a Grid dialog options

Input grid	The name of an existing grid file. Script Parameter: REGRID.IN
Output grid	The name of the output grid file. Script Parameter: REGRID.OUT
New cell size	The new cell size. If left blank, the cell size of the input grid is used Script Parameter: REGRID.CELL
Number of cells to extend beyond edge	Enter the number of grid cells to extend beyond the edge of the original grid. Script Parameter: REGRID.EDGECELL
Low-pass filter cutoff	The low-pass filter cutoff wavelength. A low-pass (smoothing) filter can be applied to each input grid line before regridding. Note that this effectively filters the grid in the grid line direction only. Script Parameter: REGRID.LOW_PASS
High-pass filter cutoff	The high-pass filter cutoff wavelength. A high-pass filter can be applied to each input grid line before re-gridding in order to remove long-wavelength features from the grid. Note that this effectively filters the grid in the grid line direction only Script Parameter: REGRID.HIGH_PASS
Non-linear filter tolerance	If entered, a non-linear filter is applied to remove noise narrower than the low-pass wavelength defined above, and greater in amplitude than the tolerance specified here. Script Parameter: REGRID.NL_TOL
Interpolation spline	Select the interpolation spline method. 0 linear spline 1 cubic (minimum curvature) spline 2 akima spline 3 Nearest Script Parameter: REGRID.SPLINE
Maximum gap to interpolate	Use this parameter to fill gaps from dummies within a grid. Gaps smaller than the gap (in your coordinate system units) will be interpolated using the selected spline method. Remember that the gap is the distance between cell centers, so if the cell size is 50 m, and one grid cell value is a dummy, then a gap of 100 is required to fill it. If a value of 0 is entered, all interior gaps will be interpolated. If no value is entered, then a gap of 1.8 times the cell size is used – this effectively means that gaps are left as they are (if the cell size remains the same). By default this field is left blank, and no interpolation of gaps is performed. Script Parameter: REGRID.GAP
Trend angle (deg. ccw from +X)	Trend angle degree ccw from +X. $image\ebx_1610156733.jpg$ Script Parameters: REGRID.TRA
Row orientation	Select the grid direction "default", "For vertical lines (KX = 1)", "for horizontal lines (KX = -1). The output grid direction parameter (represented by KX) determines whether the output grid lines will be parallel to the output grid X-axis (KX = 1) or the Y-axis (KX = -1). The variable KX should be chosen such that: the first interpolation is close to the survey line direction or, the second interpolation, which defines the direction of the output grid lines, is across the survey lines. Note: If the survey lines run in the Y direction (vertical), KX should be 1; if the survey lines run in the X direction (horizontal), KX should be -1. By default, REGRID will choose KX so that the second interpolation direction is closest to perpendicular to the average line direction (i.e. the average of all lines) unless a trend angle is specified, in which case KX will be 1.

Application Notes

Optimizing Bi-Directional Re-Gridding with Oblique Structures

If linear structures in the grid are very close to either north-south or east-west, REGRID’s default settings are ideal. But if these structures are at other angles, you should override the default REGRID settings to avoid odd streaking or other non-geological results, and enhance geological trends.

The "trend angle" is intended to enhance geological features in the direction specified. Note that the angle to be specified is counter-clockwise relative to the positive X-axis (which normally points to the east).

Re-gridding with BIGRID

A useful feature of BIGRID is the ability to re-grid an existing grid by supplying a grid in place of an XYZ file. This provides a convenient method to perform any of the following operations on a grid:

change the location of a grid origin and the grid size
change a grid's cell size
rotate a grid
apply unidirectional filtering to a grid

When re-gridding grids, BIGRID treats each grid line as an XYZ survey line and applies filters to the grid lines and performs the same interpolation procedures that were discussed previously. When re-gridding grids, you should be aware of the input grid line storage sense as defined by the grid KX parameter. KX will either be a +1 to indicate that grid lines are parallel to the grid X axis (known as a right-handed grid), or -1 to indicate grid lines are parallel to the grid Y axis (a left-handed grid).

This is especially important when applying filters since the data will only be filtered in the direction of the grid storage sense. If the KX of the input grid is +1, filters will be applied in the X direction only, and the output grid will be stored in the opposite sense (KX=-1). Similarly, if the input grid storage sense is -1, filters are only applied in the Y direction and the output grid will stored in the -1 direction.

When not applying grid rotation (TRA = 0), the grid lines of the output grid will be oriented perpendicular to the grid lines of the input grid — that is KX will change value.

When re-gridding grids, the line numbers given in the report listing are the grid line numbers multiplied by 100 with a segment number added. For example, 20401 is the first segment of input grid line 204; 1203 is the third segment of grid line 12. The segments are continuous sections of data along the grid lines that are not interrupted by dummy values.