Suture Options

Use the Suture Options dialog to stitch together two grids into a single grid.

Suture Options dialog options

Suture Path	Select the suture Path, "Automatic", "Interactive", "Grid 1 Edges" or "Grid 2 Edges" (Default is Automatic). "Interactive" path selection cannot be used for multiple grid stitching. Script Parameter: GRIDSTCH.PATH
Correction Weighting	Correction weighting between grids (Default is 0.5). Script Parameter: GRIDSTCH.WEIGHTING
Correction width (cells)	The correction width, in cells, away from the suture path. Allow for at least 8 cells to ensure a smooth suture. The default is 32. Script Parameter: GRIDSTCH.WIDTH

Application Notes

The Suture Method

The Suture method defines a line at which to join the two grids. The line, of necessity, lies completely within the overlapping area of the two grids. The "cut-off" sections of the grid have no contribution to the final grid. Along the suture line the mismatch in the grid values must be corrected by adjusting the grids on either side of the path; for instance, if, at a point on the suture path, the value for Grid #1 is 1.0 larger than the value for Grid #2, the discrepancy could be eliminated by taking the average value. Points adjacent to the path point might then be adjusted so as to produce a smooth transition between the two grids. In this routine, a multi-frequency approach is used, so that corrections are spread over the two grids in proportion to the wavelength of the mismatch found along the suture path. This ensures that the transition from one grid to the other remains smooth, no matter the amplitude and wavelength of the features that the suture path crosses.

Suture Path

Options are Automatic, Interactive, Grid #1 Edges and Grid #2 Edges. If the automatic option is selected, the suture line will bisect the overlap region; every point along the line will be at approximately equal distance from the borders of the overlap region.

Interactive Suture Path Definition

If the interactive option is selected, the user defines the path to use, using the current map. (If there is no current map, one will be requested).

All suture paths must, by definition, lie within regions of overlap; moreover, the start and end of the path within these regions is pre-determined by the geometry of the overlap, and thus cannot be altered. Therefore, those parts of the user-path not intersecting the overlapping grid sections are ignored, and if the "start" and/or "end" points are not present in the user-path, the user-path is altered to use them by joining the first and last points of the user-path within the overlap to the fixed start and end points. The resulting path may not cross any dummy positions, or a non-overlapping region of the data, otherwise an error occurs. A single user-path may be used to define the path through two or more separate overlap sections by including at least one "outside" point as a space indicator between each path section through an overlap area. (All "outside" points are ignored when calculating the suture path from a user-path.)

"Postage Stamp Stitching"

"Postage stamp" stitching may be accomplished using the Grid Edge path selections. A user may have a grid to be placed entirely within a larger grid. The contents of the entire smaller grid may be preserved by selecting the Grid Edge path corresponding to that grid – the suture path will entirely enclose the smaller grid.

The path creation algorithm may run into difficulty when the Grid Edge path is selected if the boundaries of the grid are not sufficiently smooth. It may be necessary to smooth jagged edges, remove "peninsulas" or fill in "bays" using interpolation (see below) in order for the path to be determined unambiguously. The automatic option tends to produce smoother paths because of the averaging effects of using edges from both grids simultaneously and finding the mid-points between them.

Weighting

A value in the range 0 to 1 which determines how corrections are apportioned between the grids. A value of 0 indicates that all corrections are applied to Grid #1, a value of 1.0 indicates that all corrections are applied to Grid #2, and a value of 0.5 means corrections are shared equally between both grids. By default, the weighting is even between the grids; however by forcing all the corrections toward one grid or the other, the user can keep one grid unaltered following the suture process, right up to the suture path.

Correction Width

Corrections are applied adjacent to the suture path, out to a distance, which does not exceed the correction width. (The total width of the correction zone is twice the correction width. The higher the value, the longer the stitching procedure will take, because a larger area of the grid is affected.