Ubuntu Manpage: grdraster - extract subregion from a binary raster and write a grid file

NAME

       grdraster - extract subregion from a binary raster and write a grid file

SYNOPSIS

       grdraster   [   filenumber   |   "text   pattern"   ]   -Rwest/east/south/north[r]   [   -Ggrdfile   ]  [
       -Ixinc[m|c][/yinc[m|c]] ] [ -Jparameters ] [ -V ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ]

DESCRIPTION

grdraster reads a file called grdraster.info from the current working directory, the directories pointed
to by the environment variables $GMT_DATADIR and $GMT_USERDIR, or in $GMT_SHAREDIR/dbase (in that order).
The file grdraster.info defines binary arrays of data stored in scan-line format in data files. Each
file is given a filenumber in the info file. grdraster figures out how to load the raster data into a
grid file spanning a region defined by -R. By default the grid spacing equals the raster spacing. The
-I option may be used to sub-sample the raster data. No filtering or interpolating is done, however; the
x_inc and y_inc of the grid must be multiples of the increments of the raster file and grdraster simply
takes every n'th point. The output of grdraster is either grid or pixel registered depending on the
registration of the raster used. It is up to the GMT system person to maintain the grdraster.info file
in accordance with the available rasters at each site. Raster data sets are not supplied with GMT but
can be obtained by anonymous ftp and on CD-ROM (see README page in dbase directory). grdraster will list
the available files if no arguments are given. Finally, grdraster will write xyz-triplets to stdout if
no output gridfile name is given

filenumber
If an integer matching one of the files listed in the grdraster.info file is given we will use
that data set, else we will match the given text pattern with the data set description in order to
determine the data set.

-R west, east, south, and north specify the Region of interest, and you may specify them in decimal
degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and upper right map
coordinates are given instead of w/e/s/n. The two shorthands -Rg and -Rd stand for global domain
(0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively, specify
the name of an existing grid file and the -R settings (and grid spacing, if applicable) are copied
from the grid. If r is appended, you may also specify a map projection to define the shape of
your region. The output region will be rounded off to the nearest whole grid-step in both
dimensions.

OPTIONS

       -G     Name of output grid file.  If not set, the grid will be written as ASCII (or binary; see -bo  xyz-
              triplets to stdout instead.

       -I     x_inc  [and  optionally  y_inc]  is  the  grid  spacing.  Optionally,  append  a  suffix modifier.
              Geographical (degrees) coordinates: Append m to indicate arc minutes or c to indicate arc seconds.
              If one of the units e, k, i, or n is appended instead, the increment is assumed  to  be  given  in
              meter, km, miles, or nautical miles, respectively, and will be converted to the equivalent degrees
              longitude  at  the middle latitude of the region (the conversion depends on ELLIPSOID).  If /y_inc
              is given but set to 0 it will be reset equal to x_inc; otherwise it will be converted  to  degrees
              latitude.   All coordinates: If = is appended then the corresponding max x (east) or y (north) may
              be slightly adjusted to fit exactly the given increment [by default the increment may be  adjusted
              slightly  to  fit  the given domain].  Finally, instead of giving an increment you may specify the
              number of nodes desired by appending + to the supplied integer argument;  the  increment  is  then
              recalculated  from  the  number of nodes and the domain.  The resulting increment value depends on
              whether you have selected a gridline-registered or  pixel-registered  grid;  see  Appendix  B  for
              details.   Note:  if  -Rgrdfile  is used then grid spacing has already been initialized; use -I to
              override the values.

       -J     Selects the map projection. Scale is UNIT/degree, 1:xxxxx, or width in UNIT (upper case modifier).
              UNIT is cm, inch, or m, depending on the MEASURE_UNIT setting in .gmtdefaults4, but  this  can  be
              overridden  on  the  command  line by appending c, i, or m to the scale/width value.  When central
              meridian is optional, default is center  of  longitude  range  on  -R  option.   Default  standard
              parallel  is  the  equator.  For map height, max dimension, or min dimension, append h, +, or - to
              the width, respectively.
              More details can be found in the psbasemap man pages.

              CYLINDRICAL PROJECTIONS:

              -Jclon0/lat0/scale (Cassini)
              -Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
              -Jj[lon0/]scale (Miller)
              -Jm[lon0/[lat0/]]scale (Mercator)
              -Jmlon0/lat0/scale (Mercator - Give meridian and standard parallel)
              -Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and azimuth)
              -Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
              -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
              -Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
              -Jtlon0/[lat0/]scale (TM - Transverse Mercator)
              -Juzone/scale (UTM - Universal Transverse Mercator)
              -Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)

              CONIC PROJECTIONS:

              -Jblon0/lat0/lat1/lat2/scale (Albers)
              -Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
              -Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
              -Jpoly/[lon0/[lat0/]]scale ((American) Polyconic)

              AZIMUTHAL PROJECTIONS:

              -Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
              -Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
              -Jflon0/lat0[/horizon]/scale (Gnomonic)
              -Jglon0/lat0[/horizon]/scale (Orthographic)
              -Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale (General Perspective).
              -Jslon0/lat0[/horizon]/scale (General Stereographic)

              MISCELLANEOUS PROJECTIONS:

              -Jh[lon0/]scale (Hammer)
              -Ji[lon0/]scale (Sinusoidal)
              -Jkf[lon0/]scale (Eckert IV)
              -Jk[s][lon0/]scale (Eckert VI)
              -Jn[lon0/]scale (Robinson)
              -Jr[lon0/]scale (Winkel Tripel)
              -Jv[lon0/]scale (Van der Grinten)
              -Jw[lon0/]scale (Mollweide)

              NON-GEOGRAPHICAL PROJECTIONS:

              -Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
              -Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log, and power scaling)

       -V     Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].

       -bo    Selects binary output.  Append s for single precision [Default is d (double)].  Uppercase S  or  D
              will  force  byte-swapping.  Optionally, append ncol, the number of desired columns in your binary
              output file.  This option applies only if no -G option has been set.

EXAMPLES

       To extract data from raster 1, taking one point every 30 minutes, in an area extended beyond 360  degrees
       to allow later filtering, run

       grdraster 1 -R-4/364/-62/62 -I 30m -G data.grd

       To  obtain  data  for  an oblique Mercator projection we need to extract more data that is actually used.
       This is necessary because the output of grdraster has edges defined by parallels and meridians, while the
       oblique map in general does not.  Hence, to get all the data from  the  ETOPO2  data  needed  to  make  a
       contour  map for the region defined by its lower left and upper right corners and the desired projection,
       use

       grdraster ETOPO2 -R 160/20/220/30r -Joc 190/25.5/292/69/1 -G data.grd

       To extract data from the 2 min Geoware relief blend and write it as binary double precision  xyz-triplets
       to standard output:

       grdraster "2 min Geoware" -R 20/25/-10/5  -bo >! triplets.b

REFERENCES