I want to extract from a
RasterLayer all boundary cells between classes (possibly according to the 4-cell rule), excluding from this operation cells that neighbour NA cells
raster::boundaries function detects boundaries as cells that have more than one class (including NA) cells in the 4 or 8 cells surrounding it , or, if
classes argument is set to
FALSE, cells with values and cells with NA.
What about if I do not want to consider as edge the NA border?