The Overlap Grid File

Get Relative Shift/Scales reads the overlap points from the OverlapPoints File, calculates the best possible adjustment for each overlapping grid pair, and outputs the results to an Overlap Grids File. A portion of an OverlapGrids File is shown below.

  ascale  2.51419  ashift   3.44850  npolap   36712  spread    102.3  weight    1.0  stderr    3.491  igrd1    8  igrd2   12  grid1 rSA0577k.ers      grid2 rSA0716_A8k.ers

  ascale  1.18732  ashift   0.36590  npolap   24099  spread     47.9  weight    1.0  stderr    0.459  igrd1    8  igrd2   14  grid1 rSA0577k.ers      grid2 rSA0718_A10k.ers

  ascale  0.58425  ashift   0.11527  npolap    4285  spread     42.1  weight    1.0  stderr    0.203  igrd1    8  igrd2   16  grid1 rSA0577k.ers      grid2 rSA1098k.ers

  ascale  1.46683  ashift   0.75999  npolap   18320  spread     87.4  weight    1.0  stderr    0.894  igrd1    9  igrd2   11  grid1 rSA0700_A1k.ers   grid2 rSA0700_A5k.ers

  ascale  0.94776  ashift  -0.02902  npolap   40141  spread    136.1  weight    1.0  stderr    0.262  igrd1    9  igrd2   17  grid1 rSA0700_A1k.ers   grid2 rSA1101k.ers

  ascale  1.26639  ashift   0.65855  npolap   20249  spread     74.9  weight    1.0  stderr    0.821  igrd1   10  igrd2   15  grid1 rSA0700_A3k.ers   grid2 rSA0858k.ers

  ascale  0.45026  ashift   0.11805  npolap   15999  spread     48.1  weight    1.0  stderr    0.571  igrd1   11  igrd2   12  grid1 rSA0700_A5k.ers   grid2 rSA0716_A8k.ers

  ascale  0.33192  ashift  -1.43696  npolap    6580  spread     52.5  weight    1.0  stderr    1.443  igrd1   12  igrd2   14  grid1 rSA0716_A8k.ers   grid2 rSA0718_A10k.ers

  ascale  0.06434  ashift  -0.77143  npolap   18048  spread     98.2  weight    1.0  stderr    0.776  igrd1   12  igrd2   16  grid1 rSA0716_A8k.ers   grid2 rSA1098k.ers

  ascale  0.14097  ashift  -0.67030  npolap   28961  spread    124.7  weight    1.0  stderr    0.683  igrd1   13  igrd2   16  grid1 rSA0717_A9k.ers   grid2 rSA1098k.ers

  ascale  0.25730  ashift   0.57283  npolap    2575  spread    155.2  weight    1.0  stderr    0.578  igrd1    9  igrd2   18  grid1 rSA0700_A1k.ers   grid2 CLINE

  ascale  0.03530  ashift   0.30440  npolap    2751  spread    133.1  weight    1.0  stderr    0.314  igrd1   12  igrd2   18  grid1 rSA0716_A8k.ers   grid2 CLINE

  ascale  0.07686  ashift   0.36612  npolap     850  spread     54.0  weight    1.0  stderr    0.372  igrd1   13  igrd2   18  grid1 rSA0717_A9k.ers   grid2 CLINE

  ascale  0.03595  ashift   0.24054  npolap    2304  spread    156.0  weight    1.0  stderr    0.249  igrd1   15  igrd2   18  grid1 rSA0858k.ers      grid2 CLINE

  ascale  0.58271  ashift   0.78316  npolap   13524  spread    368.8  weight    1.0  stderr    0.789  igrd1   16  igrd2   18  grid1 rSA1098k.ers      grid2 CLINE

Each row of the file represents one overlap. "CLINE" refers to control lines. The columns are the estimated scale and shift, the number of points in the overlap, the spatial spread of the overlaps (in km), a weighting factor, and the standard deviation of the differences in the overlap. The default weight for each overlap that is used to estimate the absolute shift and scales for each grid is 1.0. The user can edit the file to adjust the weights up or down to give an overlap a greater or lesser influence on the inversion. Rows can be deleted entirely to remove an overlap from consideration.

As indicated in Grid Merging Fundamentals, there is always an inconsistency in the data. This inconsistency manifests as misfits that tend to be evenly distributed through the final grid overlaps. By adjusting the weights of certain overlaps, the user can force the inconsistency (misfit) into areas of the merged grid where they may be less conspicuous.