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