
                       BUILDING CUSTOM FILTERS

The user may wish to model interactions across a landscape or remove
systematic distortion occurring across a map or image.  Both
applications can be accomplished by filtering data.  Custom filters can
be built which make the value of one pixel a user-defined function of
the values in the surrounding \cells\.  

The GRASS programs that can be used to build custom filters are:

	\-  i.zc \
	\-  r.mapcalc \
	\-  r.mfilter \
	\-  r.neighbors \ 

For more information on a specific command, select a command and press
ESC.










