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==Difference==
'''"-dif"'''<br>
Takes the difference between the first two .asc filesgrids, the second gridoutput is subtractedthe fromfirst grid minus the firstsecond grid. If an optional third .asc filegrid is specified, this is used as the output file, otherwise, grid_to_grid creates its own output filename using the names of the two input grids.asc files. The output is the first .asc file minus the second .asc file.
Two .asc grids are output:
*The first is the difference values between the two grids.asc files. A difference value only occurs at grid cells that have a value in both grids. If the cell has a null value (iei.e. the TUFLOW output was dry at that location) in either or both .asc grids, a null value is output.
*A second grid with a “_wd” suffix is output to indicate which .asc grid cells were once wet and are now dry (value -99) or oncewere dry and are now wet (value +99). withFirst first .ascgrid to be the developed case and second .ascgrid to be the existing case). Importing this grid into Vertical Mapper creates a .grc (grid classification) grid that has two categories: “Was Wet Now Dry” and “Was Dry Now Wet”. This grid is particularly useful for displaying areas that were previously inundated or previously flood-free.<br>
Example:
*Creates new grids comparing the differences in flood levels and extents for: "difference.tif" = "after_h.tif" - "before_h.tif"<br>
:<tt>grid_to_grid.exe -out difference.tif -dif after_h.tif before_h.tif</tt> ▼*Runs a difference operation on GeoTIFF outputs.<br>
:<tt>grid_to_grid.exe -dif proposed.tif existing.tif</tt>
*As above with specified output name "difference.tif"<br>
▲:<tt>grid_to_grid.exe -out difference.tif -dif after_hproposed.tif before_hexisting.tif</tt>
* Runs a difference operation on GPKG outputs. The layer name needed is assumed to be the same as the database name.<br>
:<tt>grid_to_grid.exe -dif proposed.gpkg existing.gpkg</tt>
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