Select data subsets based on multiple spatial criteria
gmtselect [ infiles ] [ -Amin_area[/min_level/max_level] ] [ -C[f]dist/ptfile ] [ -Dresolution ] [ -Fpolygonfile ] [ -H[nrec] ] [ -I[cflrs] ] [ -Jparameters ] [ -L[dist/linefile] ] [ -M[flag] ] [ -Nmaskvalues[o] ] [ -Rwest/east/south/north[r] ] [ -V ] [ -: ] [ -bi[s][n] ] [ -bo[s][n] ]
gmtselect is a filter that reads (longitude, latitude) positions from the first 2 columns of infiles [or standard input] and uses a combination of 1-5 criteria to pass or reject the records. Records can be selected based on whether or not they are 1) inside a rectangular region (-R [and -J]), 2) within dist km of any point in ptfile, 3) within dist km of any line in linefile, 4) inside one of the polygons in the polygonfile, and 5) inside geographical features (based on coastlines). The sense of the tests can be reversed for each of these 5 criteria by using the -I option. See option -: on how to read (latitude,longitude) files.
No space between the option flag and the associated arguments. Use upper case for the
option flags and lower case for modifiers.
infiles
ASCII (or binary, see-b) data file(s) to be operated on. If not given, standard input is read.
-A
Ignored unless -N is set. Geographical features with an area smaller than min_area in km^2 or of hierarchical level that is lower than min_level or higher than max_level will be ignored [Default is 0/4 (all features)]. See DATABASE INFORMATION in the pscoast man-pages for more details.
-C
Pass all records whose location is within dist km of any of the points in ptfile. If dist is zero then the 3rd column of ptfile must have each point's individual radius of influence. Prepend f to indicate you want approximate flat' earth distance calculations (faster) than exact great circle calculations (slower).
-D
Ignored unless -N is set. Selects the resolution of the coastline 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]. Note that because the coastlines differ in details is not guaranteed that a point will remain inside [or outside] when a different resolution is selected.
-F
Pass all records whose location is within one of the closed polygons in the multiple-segment file polygonfile.
-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
Reverses the sense of the test for each of the criteria specified:
c select records NOT inside any point's circle of influence.'
f select records NOT inside any of the polygons.
l select records NOT within the specified distance of any line.
r select records NOT inside the specified rectangular region.
s select records NOT considered inside as specified by -A, -D, -N.
-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 .gmtdefaults, but this can be overridden on the command line by appending the c, i, or m to the scale/width value.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard parallel)
-Joalon0/lat0/azimuth/scale (Oblique Mercator - point and azimuth)
-Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
-Jqlon0/scale (Equidistant Cylindrical Projection (Plate Carree))
-Jtlon0/scale (TM - Transverse Mercator, with Equator as y = 0)
-Jtlon0/lat0/scale (TM - Transverse Mercator, set origin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0/scale (Lambert).
-Jelon0/lat0/scale (Equidistant).
-Jflon0/lat0/horizon/scale (Gnomonic).
-Jglon0/lat0/scale (Orthographic).
-Jslon0/lat0/[slat/]scale (General Stereographic)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert)
MISCELLANEOUS PROJECTIONS:
-Jhlon0/scale (Hammer)
-Jilon0/scale (Sinusoidal)
-Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
-Jnlon0/scale (Robinson)
-Jrlon0/scale (Winkel Tripel)
-Jvlon0/scale (Van der Grinten)
-Jwlon0/scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin] (polar (theta,r) coordinates, optional a for azimuths and offset theta [0])
-Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power scaling)
More details can be found in the psbasemap manpages.
-L
Pass all records whose location is within dist km of any of the line segments in the multiple-segment file linefile. If dist is zero then the 2nd column of each sub-header in the ptfile must have each lines's individual distance value.' If no arguments are given, it means instead that the x column contains longitudes, which may differ from the region 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
Pass all records whose location is inside specified geographical features. Specify if records should be skipped or kkept using 1 of 2 formats:
-Nwet/dry.
-Nocean/land/lake/island/pond.
Append o to let points exactly on feature boundaries be considered outside the feature [Default is inside]. [Default is s/k/s/k/s (i.e., s/k), which passes all points on dry land].
-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. If no map projection is supplied we implicitly set -Jx1.
-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 geographic 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 2 input columns].
-bo
Selects binary output. Append s for single precision [Default is double].
To extract the subset of data set that is within 300 km of any of the points in pts.d but more than 100 km away from the lines in lines.d, try
gmtselect lonlatfile -Jd1d -C300/pts.d -L100/lines.d -Il > subset
Here, you must specify a mapprojection so that knows you are giving it geographical data (otherwise 300 would be interpreted as Cartesian distance in x-y units instead of km). To keep all points in data.d except those on land, as determined by the high-resolution coastlines, try
gmtselect data.d -R120/121/22/24 -Dh -Ns/k > subset
gmtdefaults(1gmt), gmt(1gmt), grdlandmask(1gmt), pscoast(1gmt)