Provided by: gmt_4.5.11-1build1_amd64 bug


       grdmask - Create mask grid files from xy paths.


       grdmask        pathfiles        -Gmask_grd_file]       -Ixinc[unit][=|+][/yinc[unit][=|+]]
       -Rwest/east/south/north[r] [ -A[m|p] ] [  -F  ]  [  -H[i][nrec]  ]  [  -Nout/edge/in  ]  [
       -Ssearch_radius[m|c|k|K]  ]  [  -V  ]  [  -:[i|o]  ]  [ -bi[s|S|d|D[ncol]|c[var1/...]] ] [
       -fcolinfo ] [ -m[flag] ]


       grdmask can operate in two different modes. 1. It reads one or  more  xy-files  that  each
       define  a  closed  polygon.  The nodes defined by the specified region and lattice spacing
       will be set equal to one of three  possible  values  depending  on  whether  the  node  is
       outside,  on the polygon perimeter, or inside the polygon.  The resulting mask may be used
       in subsequent operations involving grdmath to mask out data from polygonal areas.  2.  The
       xy-files  simply  represent  data  point  locations  and  the mask is set to the inside or
       outside value depending on whether a node is within a maximum distance  from  the  nearest
       data point.  If the distance specified is zero then only the nodes nearest each data point
       are considered "inside".

              The name of 1 or more ASCII [or binary, see -b] files  holding  the  polygon(s)  or
              data points.

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

       -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.

       -R     xmin, xmax, ymin, and ymax specify the Region of interest.  For geographic regions,
              these limits correspond to west, east, south, and north and you may specify them in
              decimal degrees or in [+-]dd:mm[][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.   For  calendar  time  coordinates  you  may  either  give  (a) relative time
              (relative to the selected TIME_EPOCH and in the selected  TIME_UNIT;  append  t  to
              -JX|x),  or  (b)  absolute time of the form [date]T[clock] (append T to -JX|x).  At
              least one of date and clock must be present; the T is always  required.   The  date
              string must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]]
              (ISO week calendar), while the clock string must be  of  the  form  hh:mm:ss[.xxx].
              The  use  of  delimiters  and their type and positions must be exactly as indicated
              (however, input, output and plot formats are customizable; see gmtdefaults).


       -A     If the input data are geographic (as indicated  by  -fi)  then  the  sides  in  the
              polygons  will  be approximated by great circle arcs.  When using the -A sides will
              be regarded as straight lines.  Alternatively, append m to have sides first  follow
              meridians, then parallels. Or append p to first follow parallels, then meridians.

       -F     Force   pixel   node   registration  [Default  is  gridline  registration].   (Node
              registrations are defined in GMT Cookbook Appendix B on grid file formats.)

       -H     Input file(s) has header record(s).  If used, the default number of header  records
              is  N_HEADER_RECS.   Use -Hi if only input data should have header records [Default
              will write out header records if the input data have them]. Blank lines  and  lines
              starting with # are always skipped.

       -N     Sets  the  values  that will be assigned to nodes that are outside the polygons, on
              the edge, or inside.  Values can  be  any  number,  including  the  textstring  NaN
              [Default is 0/0/1].

       -S     Set  nodes  depending  on their distance from the nearest data point.  Nodes within
              radius [0] from a data point are considered inside.  Append m to  indicate  minutes
              or  c  to  indicate  seconds.   Append  k  to indicate km (implies -R and -I are in
              degrees, and we will use a fast flat Earth approximation  to  calculate  distance).
              For  more  accuracy,  use  uppercase  K  if  distances  should  be calculated along
              geodesics.  However, if the  current  ELLIPSOID  is  spherical  then  great  circle
              calculations  are used.  If -S is not set then we consider the input data to define
              closed polygon(s) instead.

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

       -bi    Selects  binary  input.   Append  s  for  single precision [Default is d (double)].
              Uppercase S or D will force byte-swapping.  Optionally, append ncol, the number  of
              columns  in your binary input file if it exceeds the columns needed by the program.
              Or append c if the input  file  is  netCDF.  Optionally,  append  var1/var2/...  to
              specify the variables to be read.  [Default is 2 input columns].

       -f     Special  formatting  of  input  and/or  output columns (time or geographical data).
              Specify i or o to make this apply only to  input  or  output  [Default  applies  to
              both].   Give one or more columns (or column ranges) separated by commas.  Append T
              (absolute calendar time), t (relative time in chosen TIME_UNIT since TIME_EPOCH), x
              (longitude),  y  (latitude),  or  f (floating point) to each column or column range
              item.  Shorthand -f[i|o]g means -f[i|o]0x,1y (geographic coordinates).

       -m     Multiple segment file.  Segments are separated by a record whose first character is
              flag.  [Default is '>'].


       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 "packing" of grids, writing out floating point
       data as 2- or 4-byte integers. To specify the precision, scale and offset, the user should
       add  the  suffix =id[/scale/offset[/nan]], 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  nan is the value used to indicate missing data.  See
       grdreformat(1) and Section 4.17 of the GMT  Technical  Reference  and  Cookbook  for  more

       When  writing  a netCDF file, the grid is stored by default with the variable name "z". 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.


       When the output grid  type  is  netCDF,  the  coordinates  will  be  labeled  "longitude",
       "latitude", or "time" based on the attributes of the input data or grid (if any) or on the
       -f or -R options. For example, both -f0x -f1t  and  -R  90w/90e/0t/3t  will  result  in  a
       longitude/time grid. When the x, y, or z coordinate is time, it will be stored in the grid
       as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH in the  .gmtdefaults
       file  or  on  the command line.  In addition, the unit attribute of the time variable will
       indicate both this unit and epoch.


       To set all nodes inside and on the polygons coastline_*.xy to 0, and outside points to  1,

       grdmask coastline_*.xy -R-60/-40/-40/-30 -I 5m -N 1/0/0 -G land_mask.grd -V

       To set nodes within 50 km of data points to 1 and other nodes to NaN, do

       grdmask -R-60/-40/-40/-30 -I 5m -N NaN/1/1 -S 50k -G data_mask.grd -V


       GMT(1), grdlandmask(1), grdmath(1), grdclip(1), psmask(1), psclip(1)