RGMAP MEMORY_OPTIONS

        The program normally allocates less that 1/5 of the total number  of
    pixels in the map to store the contour segments, and warns the user when
    that limit is reached. Besides, contouring may be slow  on  large  maps.
    The  modifier  "Fast"  cuts  the  map  in  smaller "chunks" and performs
    contouring on those submaps, without the 1/5 above limitation.

    The Contour-filling mode (/GREY) can consume (temporary) a large  amount
    of  memory,  so  is  always performed on subsets of the image ("chunks")
    when the image size is greater than a system-dependent limit (256*256 on
    UNIX systems). When the contours are too involved, an internal limit can
    nevertheless be reached. One  can  then  retry  the  contour-filling  by
    specifying  a  smaller  "Chunksize"  (in  pixels). For example, to force
    contour-filling on subsets of 64 "lines" of a 512x512 pixel image,  type
    RGMAP 64*512 /GREY