Twin directories of rop:

[DIR]  ftp://ftp.nerc.com/pub/sys/all_updl/rop/
[DIR]  ftp://ftp.linuxforum.hu/mirrors/frugalware/pub/other/e17/e17/proto/enesim/src/lib/raster/surface/rop/
[DIR]  ftp://ftp.gfdl.gov/pub/rop/