MINMAX(l) MINMAX(l)
NAME
minmax - Find extreme values in data tables
SYNOPSIS
minmax [ files] [ -C ] [ -D ] [ -H[nrec] ] [ -Idx[/dy] ] [ -L ] [ -M[flag] ] [ -: ] [ -bi[s][n] ]
DESCRIPTION
minmax reads its standard input [or from files] and finds the extreme values in each of the columns. It recognizes NaNs and will print
warnings if the number of columns vary from record to record. As an option, minmax will find the extent of the first two columns rounded
up and down to the nearest multiple of dx/dy. This output will be in the form -Rw/e/s/n which can be used directly in the command line for
other programs, or simply in column form.
xyzfile
ASCII [or binary, see -b] file(s) holding a fixed number of data columns.
OPTIONS -C Report the min/max values per column in separate columns [Default uses <min/max> format]
-D Sets longitude discontinuity to the Dateline (-180/+180) [Default is Greenwich (0-360)]. Requires -L.
-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.
-I Report the min/max of the first two columns to the nearest multiple of dx and dy, and output this in the form -Rw/e/s/n (unless -C
is set).
-L Indicates that the x column contains longitudes, which may be periodic in 360 degrees [Default assumes no periodicity].
-M Multiple segment file(s). Segments are separated by a special record. For ASCII files the first character must be flag [Default is
'>']. For binary files all fields must be NaN.
-: Toggles between (longitude,latitude) and (latitude,longitude) input/output. [Default is (longitude,latitude)]. Applies to geo-
graphic coordinates only. Only works when -I is selected.
-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 find the extreme values in the file ship_gravity.xygd, try
minmax ship_gravity.xygd
Output should look like
ship_gravity.xygd: N = 6992 <326.125/334.684> <-28.0711/-8.6837> <-47.7/177.6> <0.6/3544.9>
To find the extreme values in the file track.xy to the nearest 5 units and use this region to draw a line using psxy, try
psxy `minmax -I5 track.xy` track.xy -Jx1 -B5 -P > track.ps
To find the min and max values for each column, but rounded to integers, try
minmax junkfile -C -I1
SEE ALSO gmt(1gmt)
1 Jan 2004 MINMAX(l)
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NEARNEIGHBOR(l) NEARNEIGHBOR(l)
NAME
nearneighbor - A "Nearest neighbor" gridding algorithm
SYNOPSIS
nearneighbor [ xyzfile(s) ] -Gout_grdfile -Ix_inc[m|c][/y_inc[m|c]] -Nsectors -Rwest/east/south/north[r] -Ssearch_radius[m|c|k|K] [ -Eempty
] [ -F ] [ -H[nrec] ] [ -L[flag] ] [ -V ] [ -W ] [ -: ] [ -bi[s][n] ]
DESCRIPTION
nearneighbor reads arbitrarily located (x,y,z[,w]) triples [quadruplets] from standard input [or xyzfile(s)] and uses a nearest neighbor
algorithm to assign an average value to each node that have one or more points within a radius centered on the node. The average value is
computed as a weighted mean of the nearest point from each sector inside the search radius. The weighting function used is w(r) = 1.0 / (1
+ d ^ 2), where d = 3 * r / search_radius and r is distance from the node. This weight is modulated by the observation points' weights [if
supplied].'
xyzfile(s)
3 [or 4, see -W] column ASCII file(s) [or binary, see -b] holding (x,y,z[,w]) data values. If no file is specified, nearneighbor
will read from standard input.
-G Give the name of the output grdfile.
-I x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds.
-N The circular area centered on each node is divided into several sectors. Average values will only be computed if there is at least
one value inside each of the sectors for a given node. Nodes that fail this test are assigned the value NaN (but see -E). [Default
is quadrant search, i.e., sectors = 4]. Note that only the nearest value per sector enters into the averaging, not all values inside
the circle.
-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.
-S Sets the search_radius in same units as the grid spacing; append m to indicate minutes or c to indicate seconds. Append k to indi-
cated km (implies -R -I are in degrees); use uppercase K if distances should be calculated using great circles [k uses flat Earth].
OPTIONS -E Set the value assigned to empty nodes [NaN].
-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. Not used with binary data.
-L Boundary condition flag may be x or y or xy indicating data is periodic in range of x or y or both set by -R, or flag may be g indi-
cating geographical conditions (x and y are lon and lat). [Default is no boundary conditions]. If no flag is given, it is assumed
that the x column contains longitudes, which may differ from the region in -R by [multiples of] 360 degrees [Default assumes no
periodicity].
-V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
-: Toggles between (longitude,latitude) and (latitude,longitude) input/output. [Default is (longitude,latitude)]. Applies to geo-
graphic coordinates only.
-W Input data have a 4th column containing observation point weights. These are multiplied with the geometrical weight factor to deter-
mine the actual weights used in the calculations.
-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].
EXAMPLES
To create a gridded data set from the file seaMARCII_bathy.lon_lat_z using a 0.5 min grid, a 5 km search radius, using an octant search,
and set empty nodes to -9999, try
nearneighbor seaMARCII_bathy.lon_lat_z -R242/244/-22/-20 -I.5m -E-9999 -Gbathymetry.grd -S5k -N8
To make a global gridded file from the data in geoid.xyz using a 1 degree grid, a 200 km search radius, spherical distances, using an quad-
rant search, and set empty nodes to NaN, try
nearneighbor geoid.xyz -R0/360/-90/90 -I1 -Lg -Ggeoid.grd -S20K -N4
SEE ALSO blockmean(1gmt), blockmedian(1gmt), blockmode(1gmt), gmt(1gmt), surface(1gmt), triangulate(1gmt)
1 Jan 2004 NEARNEIGHBOR(l)