grdmask(1) [debian man page]
GRDMASK(l) GRDMASK(l) NAME
grdmask - Create mask grdfiles from xy paths. SYNOPSIS
grdmask pathfiles -Gmask_grd_file] -Ixinc[m|c][/yinc[m|c]] -Rwest/east/south/north[r] [ -A ] [ -F ] [ -H[nrec] ] [ -L ] [ -M[flag] ] [ -Nout/edge/in ] [ -S[radius][k] ] [ -V ] [ -: ] [ -bi[s][n] ] DESCRIPTION
grdmask can operate in 2 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 grdfile 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 depend- ing 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". pathfiles 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 grd file. -I x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds. -R west, east, south, and north specify the Region of interest. To specify boundaries in degrees and minutes [and seconds], use the dd:mm[:ss] format. Append r if lower left and upper right map coordinates are given instead of wesn. OPTIONS
-A If the input data are geographic (as indicated by -L) then the sides in the polygons will be approximated by great circle arcs. This can be turned off using the -A switch. -F Force pixel registration. [Default is grid registration]. -H Input file(s) has Header record(s). Number of header records can be changed by editing your .gmtdefaults file. If used, GMT default is 1 header record. -L Indicates that the x column contains longitudes, which may differ from the regions in -R by [multiples of] 360 degrees [Default assumes no periodicity]. -M Multiple segment file. Segments are separated by a record whose first character is flag. [Default is '>']. -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 k to indicate map units (e.g., -R -I in degrees and radius in km). -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. -bi Selects binary input. Append s for single precision [Default is double]. Append n for the number of columns in the binary file(s). [Default is 2 input columns]. EXAMPLES
To set all nodes inside and on the polygons coastline_*.xy to 0, and outside points to 1, do grdmask coastline_*.xy -R-60/-40/-40/-30 -I5m -N1/0/0 -Gland_mask.grd -V To set nodes within 50 km of data points to 1 and other nodes to NaN, do grdmask data.xyz -R-60/-40/-40/-30 -I5m -NNaN/1/1 -S50k -Gdata_mask.grd -V SEE ALSO
gmt(1gmt), grdlandmask(1gmt), grdmath(1gmt), grdclip(1gmt), psmask(1gmt), psclip(1gmt) 1 Jan 2004 GRDMASK(l)
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BLOCKMEDIAN(l) BLOCKMEDIAN(l) NAME
blockmedian - filter to block average (x,y,z) data by L1 norm. SYNOPSIS
blockmedian [ xyz[w]file(s) ] -Ix_inc[m|c][/y_inc[m|c]] -Rwest/east/south/north[r] [ -C ] [ -F ] [ -H[nrec] ] [ -L ] [ -Q ] [ -V ] [ -W[io] ] [ -: ] [ -bi[s][n] ] [ -bo[s][n] ] DESCRIPTION
blockmedian reads arbitrarily located (x,y,z) triples [or optionally weighted quadruples (x,y,z,w)] from standard input [or xyz[w]file(s)] and writes to standard output a median position and value for every non-empty block in a grid region defined by the -R and -I arguments. Either blockmean, blockmedian, or blockmode should be used as a pre-processor before running surface to avoid aliasing short wavelengths. These routines are also generally useful for decimating or averaging (x,y,z) data. You can modify the precision of the output format by editing the D_FORMAT parameter in your .gmtdefaults file, or you may choose binary input and/or output using single or double precision storage. xyz[w]file(s) 3 [or 4] column ASCII file(s) [or binary, see -b] holding (x,y,z[,w]) data values. [w] is an optional weight for the data. If no file is specified, blockmedian will read from standard input. -I x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds. -R west, east, south, and north specify the Region of interest. To specify boundaries in degrees and minutes [and seconds], use the dd:mm[:ss] format. Append r if lower left and upper right map coordinates are given instead of wesn. OPTIONS
-C Use the center of the block as the output location [Default uses the median location (but see -Q)]. -C overrides -Q. -F Block centers have pixel registration. [Default: grid registration.] (Registrations are defined in GMT Cookbook Appendix B on grid file formats.) Each block is the locus of points nearest the grid value location. For example, with -R10/15/10/15 and and -I1: with the -F option 10 <= (x,y) < 11 is one of 25 blocks; without it 9.5 <= (x,y) < 10.5 is one of 36 blocks. -H Input file(s) has Header record(s). Number of header records can be changed by editing your .gmtdefaults file. If used, GMT default is 1 header record. Not used with binary data. -L Indicates that the x column contains longitudes, which may differ from the region in -R by [multiples of] 360 degrees [Default assumes no periodicity]. -Q (Quicker) Finds median z and (x, y) at that z [Default finds median x, median y, median z]. -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. -W Weighted modifier[s]. Unweighted input and output has 3 columns x,y,z; Weighted i/o has 4 columns x,y,z,w. Weights can be used in input to construct weighted median values in blocks. Weight sums can be reported in output for later combining several runs, etc. Use -W for weighted i/o, -Wi for weighted input only, -Wo for weighted output only. [Default uses unweighted i/o] -: Toggles between (longitude,latitude) and (latitude,longitude) input/output. [Default is (longitude,latitude)]. Applies to geo- graphic coordinates only. -bi Selects binary input. Append s for single precision [Default is double]. Append n for the number of columns in the binary file(s). [Default is 3 (or 4 if -W is set) columns]. -bo Selects binary output. Append s for single precision [Default is double]. EXAMPLES
To find 5 by 5 minute block medians from the double precision binary data in hawaii_b.xyg and output an ASCII table, try blockmedian hawaii_b.xyg -R198/208/18/25 -I5m -bi3 > hawaii_5x5.xyg SEE ALSO
blockmean(1gmt), blockmode(1gmt), gmt(1gmt), gmtdefaults(1gmt), nearneighbor(1gmt), surface(1gmt), triangulate(1gmt) 1 Jan 2004 BLOCKMEDIAN(l)