## Filter Grid

Option on Raster GIS menu, **Filter**

**Filter**: creates a new grid, leaving the original unchanged. This
cannot operate on the original grid in place because it requires the unchanged
neighborhood values.
**Filter grid with .fil file**--filter
the current grid, using a matrix with custom
values.
- Enter value for number of pixels to go out
in each direction--for instance a value of 2 will
create a 5x5 filter.
** **(this
allows much bigger filters than the Filter grid
command, but will be slower)
**Mode (majority filter)**--only for byte grids, replaces
the value with the most common one in the 3x3 or 5x5
neighborhood.
**Median filte**r: Replaces with
median value in the box.
**Mean filter: **Replaces with
mean (average) value in the box.
**Minimum filte**r: Replaces with
lowest value in the box.
**Maximum filte**r: Replaces with
highest value in the box.
**Parametric isotropic smoothing**:
recommended by Hengl and Evans (2008,
after Sharry and others, 2002) before
computing curvature or other derivatives.
**Vector average**: smooths circular data like aspects.
**Std Deve in box**: Replaces with the standard
deviation in the region
**Sum in box:** sums values within box.
**Filled neighborhood**: Pick minimum number of points that must be present in the
region. Points not meeting the criteria will be
removed from the grid.
**Number immediate neighbors**: new grid with the number of
immediate neighbors in a specified region size
- Isolated values
**Edges **
**RGB grid fill holes**
**Detrend DEM/grid: **select a radius in
pixels for a square mean filter, and a new DEM will be
creating subtracting the result of the filter from the
original DEM elevation

"Filter grids to edge", set on **Grids
tab of **the **Options** form, allows
filtering to the edge of data set, even if the filter should require points
outside the grid limits.

Filtering theory

*Last revision 7/112022*