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grdlandmask(1)                        GMT                       grdlandmask(1)




NAME

       grdlandmask - "Create a ""wet-dry"" mask grid from shoreline data base"


SYNOPSIS

       grdlandmask  -Gmask_grd_file
        -Iincrement
        -Rregion [   -Amin_area[/min_level/max_level][+ag|i|s  |S][+r|l][pper-
       cent] ] [  -Dresolution[+] ] [  -N ] [  -Nmaskvalues ] [  -V[level] ] [
       -r ] [ -x[[-]n] ]

       Note: No space is allowed between the option flag  and  the  associated
       arguments.


DESCRIPTION

       grdlandmask  reads the selected shoreline database and uses that infor-
       mation to decide which nodes in the specified grid  are  over  land  or
       over  water. The nodes defined by the selected region and lattice spac-
       ing will be set according to one of two criteria: (1) land vs water, or
       (2) the more detailed (hierarchical) ocean vs land vs lake vs island vs
       pond. The resulting mask may be used in subsequent operations involving
       grdmath to mask out data from land [or water] areas.


REQUIRED ARGUMENTS

       -Gmask_grd_file]
              Name  of resulting output mask grid file. (See GRID FILE FORMATS
              below).

       -Ixinc[unit][+e|n][/yinc[unit][+e|n]]
              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 s to indicate  arc  seconds.
              If  one of the units e, f, k, M, n or u is appended instead, the
              increment is assumed to be given in meter, foot, km, Mile,  nau-
              tical  mile  or  US  survey foot, respectively, and will be con-
              verted to the equivalent degrees longitude at the  middle  lati-
              tude  of  the region (the conversion depends on PROJ_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 coordi-
              nates: If +e 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  +n  to
              the  supplied  integer  argument; the increment is then recalcu-
              lated from the number of nodes and  the  domain.  The  resulting
              increment  value  depends  on  whether you have selected a grid-
              line-registered or pixel-registered grid;  see  App-file-formats
              for  details.  Note:  if -Rgrdfile is used then the grid spacing
              has already been initialized; use -I to override the values.

       -Rwest/east/south/north[/zmin/zmax][+r][+uunit]
              west, east, south, and north specify the region of interest, and
              you    may    specify    them   in   decimal   degrees   or   in
              [A+-]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 for grid creation, give Rcodelon/lat/nx/ny,  where
              code  is a 2-character combination of L, C, R (for left, center,
              or right) and T, M, B for top, middle, or bottom. e.g.,  BL  for
              lower  left.  This indicates which point on a rectangular region
              the lon/lat coordinate refers to, and the grid dimensions nx and
              ny with grid spacings via -I is used to create the corresponding
              region.  Alternatively, specify the name  of  an  existing  grid
              file  and  the -R settings (and grid spacing, if applicable) are
              copied from the grid. Appending +uunit expects projected (Carte-
              sian)  coordinates  compatible  with  chosen -J and we inversely
              project to determine actual rectangular geographic region.   For
              perspective view (-p), optionally append /zmin/zmax.  In case of
              perspective view (-p), a z-range (zmin, zmax) can be appended to
              indicate  the  third  dimension. This needs to be done only when
              using the -Jz option, not when using only the -p option. In  the
              latter  case a perspective view of the plane is plotted, with no
              third dimension.


OPTIONAL ARGUMENTS

       -Amin_area[/min_level/max_level][+ag|i|s|S][+r|l][+ppercent]
              Features with an area smaller than min_area in km^2 or of  hier-
              archical  level  that  is  lower  than  min_level or higher than
              max_level will not be plotted [Default is 0/0/4 (all features)].
              Level  2  (lakes)  contains  regular lakes and wide river bodies
              which we normally include  as  lakes;  append  +r  to  just  get
              river-lakes  or  +l to just get regular lakes.  By default (+ai)
              we select the ice shelf boundary as the  coastline  for  Antarc-
              tica;  append  +ag  to  instead select the ice grounding line as
              coastline.  For expert users who wish to print their own Antarc-
              tica  coastline and islands via psxy you can use +as to skip all
              GSHHG features below 60S or +aS to  instead  skip  all  features
              north  of  60S.   Finally,  append +ppercent to exclude polygons
              whose percentage area of the corresponding full-resolution  fea-
              ture  is less than percent. See GSHHG INFORMATION below for more
              details.

       -Dresolution[+]
              Selects the resolution of the data set to use  ((f)ull,  (h)igh,
              (i)ntermediate,  (l)ow, or (c)rude). The resolution drops off by
              ~80% between data sets. [Default is l].  Append +  to  automati-
              cally  select a lower resolution should the one requested not be
              available [abort if not found].  Alternatively, choose (a)uto to
              automatically  select  the  best  resolution  given  the  chosen
              region.  Note that because the coastlines differ  in  details  a
              node  in  a  mask file using one resolution is not guaranteed to
              remain inside  [or  outside]  when  a  different  resolution  is
              selected.

       -E     Indicate  that  nodes  that  fall  exactly on a polygon boundary
              should be considered to be outside the polygon [Default  consid-
              ers them to be inside].

       -Nmaskvalues
              Sets  the  values  that will be assigned to nodes. Values can be
              any number, including the textstring NaN. Also select -E to  let
              nodes  exactly  on  feature  boundaries  be  considered  outside
              [Default is inside]. Specify this information using 1 of 2  for-
              mats:

              -Nwet/dry.

              -Nocean/land/lake/island/pond.

              [Default is 0/1/0/1/0 (i.e., 0/1)].

       -V[level] (more a|)
              Select verbosity level [c].

       -r (more a|)
              Set pixel node registration [gridline].

       -x[[-]n] (more a|)
              Limit  number of cores used in multi-threaded algorithms (OpenMP
              required).

       -^ or just -
              Print a short message about the  syntax  of  the  command,  then
              exits (NOTE: on Windows just use -).

       -+ or just +
              Print  an extensive usage (help) message, including the explana-
              tion of any module-specific  option  (but  not  the  GMT  common
              options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation
              of all options, then exits.


GRID FILE FORMATS

       By default GMT  writes  out  grid  as  single  precision  floats  in  a
       COARDS-complaint  netCDF  file  format. However, GMT is able to produce
       grid files in many other commonly  used  grid  file  formats  and  also
       facilitates  so  called  apackinga of grids, writing out floating point
       data as 1- or 2-byte integers. To specify the precision, scale and off-
       set,  the user should add the suffix =ID[+sscale][+ooffset][+ninvalid],
       where ID is a two-letter identifier of the grid type and precision, and
       scale  and offset are optional scale factor and offset to be applied to
       all grid values, and invalid is the  value  used  to  indicate  missing
       data.  See grdconvert and Section grid-file-format of the GMT Technical
       Reference and Cookbook for more information.

       When writing a netCDF file, the grid is  stored  by  default  with  the
       variable  name  aza.  To  specify another variable name varname, append
       ?varname to the file name. Note that you may need to escape the special
       meaning  of  ? in your shell program by putting a backslash in front of
       it, or by placing the filename and  suffix  between  quotes  or  double
       quotes.


EXAMPLES

       To  set  all nodes on land to NaN, and nodes over water to 1, using the
       high resolution data set, do

              gmt grdlandmask -R-60/-40/-40/-30 -Dh -I5m -N1/NaN -Gland_mask.nc -V

       To make a 1x1 degree global grid with the hierarchical  levels  of  the
       nodes based on the low resolution data:

              gmt grdlandmask -R0/360/-90/90 -Dl -I1 -N0/1/2/3/4 -Glevels.nc -V


GSHHS INFORMATION

       The coastline database is GSHHG (formerly GSHHS) which is compiled from
       three sources:  World Vector Shorelines (WVS), CIA World Data  Bank  II
       (WDBII),  and Atlas of the Cryosphere (AC, for Antarctica only).  Apart
       from Antarctica, all level-1 polygons (ocean-land boundary) are derived
       from  the more accurate WVS while all higher level polygons (level 2-4,
       representing        land/lake,         lake/island-in-lake,         and
       island-in-lake/lake-in-island-in-lake boundaries) are taken from WDBII.
       The Antarctica coastlines come in two flavors: ice-front  or  grounding
       line, selectable via the -A option.  Much processing has taken place to
       convert WVS, WDBII, and AC data into usable form  for  GMT:  assembling
       closed  polygons  from line segments, checking for duplicates, and cor-
       recting for crossings between polygons.  The area of each  polygon  has
       been  determined  so  that  the  user  may  choose not to draw features
       smaller than a minimum area (see -A); one may also  limit  the  highest
       hierarchical level of polygons to be included (4 is the maximum). The 4
       lower-resolution databases were derived from the full resolution  data-
       base using the Douglas-Peucker line-simplification algorithm. The clas-
       sification of rivers and borders follow that of the WDBII. See the  GMT
       Cookbook and Technical Reference Appendix K for further details.


SEE ALSO

       gmt(1), grdmath(1), grdclip(1), psmask(1), psclip(1), pscoast(1)


COPYRIGHT

       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe



5.4.2                            Jun 24, 2017                   grdlandmask(1)

gmt5 5.4.2 - Generated Wed Jun 28 20:21:03 CDT 2017
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