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  con-
    touring 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 spec-
    ifying 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