Add/Subtract Two Grids

Use the Add/Subtract Two Grids option (GRIDADD GX) to add two grids together or subtract one grid from another to produce a new grid. Multiplying factors may be applied to each grid before the addition. Subtraction can be achieved by using multipliers of +1 and -1.

Add/Subtract Two Grids dialog options

Input grid file 1

File Name of the First Grid. (.grd file)

Script Parameter: GRIDADD.GRD1

Input grid file 2

File Name of the Second Grid. (.grd file)

Script Parameter: GRIDADD.GRD2

Multiply grid 1 by:

Multiplier to Apply to First Grid (before addition occurs). Default = 1.

Script Parameter: GRIDADD.MUL1

Multiply grid 2 by:

Multiplier to Apply to Second Grid (before addition occurs). Default = 1.

Script Parameter: GRIDADD.MUL2

New resultant grid

File Name of New Grid. (.grd file)

Script Parameter: GRIDADD.NEW

Application Notes

Addition of the grids occurs grid point by grid point. Subtract grid #2 from grid #1 by applying a multiplier of -1 to grid #2.

Following are examples where adding or subtracting grids can be useful:

  • A regional (smoothed) grid may be subtracted from the original grid to produce a residual.

  • In magnetic surveys, the IGRF (International Geomagnetic Reference Field) may be calculated at a small number of points within an area and gridded separately. This grid may then be subtracted from the total magnetic field to effectively remove the IGRF.

If grid 2 does not match grid 1 in coordinate system, grid size or cell size, it will be sampled to match grid 1 and the result grid will be spatially equivalent to grid 1.

See Also: