This file contains information on rasterfiles which are readable with
 grdraster.
 This file must be named $(GMT_GRIDDIR)/grdraster.info where GMT_GRIDDIR is an
 environment variable [$GMTHOME/share/dbase].  This file is read by grdraster
 at run time.  Any line beginning with a # will be treated as a comment, and
 blank lines are skipped.  Any other line must have the following items, all
 on one line, one line per rasterfile:

 file_number "title string" "z units" -R -I GorP type scale offset NaNflag filename [B|L]

 There must be white space between each item.  "title string" and "z units"
 must be enclosed in " ", and they may have white space within them.  They are
 limited to a maximum of 80 characters.  No other quotation marks should be on
 a line. The entire line should be writable in 320 characters.

 file_number is an integer used to tell grdraster which raster to read.  It
       must be unique to each raster.
 "title string" is a brief description of the data.
 "z units"  describes the units of the data after they are scaled and offset.
 -R /w/e/s/n/ describes the range of the raster in the GMT -R manner.
 -I /x_inc/_inc/; describes the sampling interval in the GMT -I manner.
 GorP is either G or P, indicating Grid or Pixel registration.
 type is one of the following, indicating the kind of data in the rasterfile:
       b       bit data, either 0 or 1, one bit per data value.
       u       unsigned character data.
       c       signed character data.
       d       unsigned two-byte integer data.
       i       signed two-byte integer data.
 scale is a number which should be multiplied on the raster value after read.
 offset is a number which should be added to the [scaled] raster value.
 NaNflag is a number which is written in the raster to represent NaN.
       If all values in the raster represent data, NaNflag is none.
 filename is the name the raster file.  If filename begins with a "/", then
       it will be treated as a complete name.  If not, the complete name will
       be formed as $(GMT_GRIDDIR)/filename.
 Optionally, you may append a single character (B or L) to indicate that this
 data set needs to be byte swapped on this machine.  Because binary data sets
 are not architecture-independent a file written on, say, a Solaris computer
 (type B) will have a different byte order than a PC (Linux or WIN32) (type L).
 You have two alternative ways to deal with this: 1. Compile in byte swapping.
 This occurs if the define flag -DGMTSWAP is given to the compiler, and is the
 default action when installing GMT using installgmt if the byte order differs
 from that of a Sun. 2. Append the swap flag for those data sets that need it.

 You will need to edit this to reflect which data you have installed on your
 system, and append B or L for swapping if appropriate:

01 "ETOPO2" "m" -R-180/179:58/-90/90 -I2m  G i 1 0 none /path_to_etopo2.i2