NAME¶
grdraster - extract subregion from a binary raster and write a grid file
SYNOPSIS¶
grdraster [
filenumber |
"text pattern" ]
-R west/
east/
south/
north[
r] [
-G grdfile ] [
-Ixinc[
m|
c][/
yinc[
m|
c]] ] [
-Jparameters ] [
-V ] [
-bo[
s|
S|
d|
D[
ncol]|
c[
var1 /...]] ]
DESCRIPTION¶
grdraster reads a file called
grdraster.info from the current
working directory, the directories pointed to by the environment variables
$GMT_DATADIR and
$GMT_USERDIR, or in
$GMT_SHAREDIR/dbase
(in that order). The file
grdraster.info defines binary arrays of data
stored in scan-line format in data files. Each file is given a
filenumber in the info file.
grdraster figures out how to load
the raster data into a grid file spanning a region defined by
-R. By
default the grid spacing equals the raster spacing. The
-I option may
be used to sub-sample the raster data. No filtering or interpolating is done,
however; the
x_inc and
y_inc of the grid must be multiples of
the increments of the raster file and
grdraster simply takes every n'th
point. The output of
grdraster is either grid or pixel registered
depending on the registration of the raster used. It is up to the
GMT
system person to maintain the
grdraster.info file in accordance with
the available rasters at each site. Raster data sets are not supplied with
GMT but can be obtained by anonymous ftp and on CD-ROM (see README page
in dbase directory).
grdraster will list the available files if no
arguments are given. Finally,
grdraster will write xyz-triplets to
stdout if no output gridfile name is given
- filenumber
- If an integer matching one of the files listed in the
grdraster.info file is given we will use that data set, else we
will match the given text pattern with the data set description in order
to determine the data set.
- -R
- west, east, south, and north specify the
Region of interest, and you may specify them in decimal degrees or in
[+-]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, specify the name of an existing grid file and the -R
settings (and grid spacing, if applicable) are copied from the grid. If
r is appended, you may also specify a map projection to define the
shape of your region. The output region will be rounded off to the nearest
whole grid-step in both dimensions.
OPTIONS¶
- -G
- Name of output grid file. If not set, the grid will be
written as ASCII (or binary; see -bo xyz-triplets to stdout
instead.
- -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.
- -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 .gmtdefaults4, but this can be
overridden on the command line by appending c, i, or
m to the scale/width value. When central meridian is optional,
default is center of longitude range on -R option. Default standard
parallel is the equator. For map height, max dimension, or min dimension,
append h, +, or - to the width, respectively.
More details can be found in the psbasemap man pages.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical
Stereographic)
-Jj[lon0/]scale (Miller)
-Jm[lon0/[lat0/]]scale (Mercator)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard
parallel)
-Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator -
point and azimuth)
-Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator -
two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
pole)
-Jq[lon0/[lat0/]]scale (Cylindrical
Equidistant)
-Jtlon0/[lat0/]scale (TM - Transverse Mercator)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
-Jpoly/[lon0/[lat0/]]scale ((American)
Polyconic)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0[/horizon]/scale (Lambert Azimuthal
Equal-Area)
-Jelon0/lat0[/horizon]/scale (Azimuthal
Equidistant)
-Jflon0/lat0[/horizon]/scale (Gnomonic)
-Jglon0/lat0[/horizon]/scale (Orthographic)
-Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
(General Perspective).
-Jslon0/lat0[/horizon]/scale (General
Stereographic)
MISCELLANEOUS PROJECTIONS:
-Jh[lon0/]scale (Hammer)
-Ji[lon0/]scale (Sinusoidal)
-Jkf[lon0/]scale (Eckert IV)
-Jk[s][lon0/]scale (Eckert VI)
-Jn[lon0/]scale (Robinson)
-Jr[lon0/]scale (Winkel Tripel)
-Jv[lon0/]scale (Van der Grinten)
-Jw[lon0/]scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin][r|z] (Polar
coordinates (theta,r))
-Jxx-scale[d|l|ppow|t|T][
/y-scale[d|l|ppow|t|T]]
(Linear, log, and power scaling)
- -V
- Selects verbose mode, which will send progress reports to
stderr [Default runs "silently"].
- -bo
- Selects binary output. Append s for single precision
[Default is d (double)]. Uppercase S or D will force
byte-swapping. Optionally, append ncol, the number of desired
columns in your binary output file. This option applies only if no
-G option has been set.
EXAMPLES¶
To extract data from raster 1, taking one point every 30 minutes, in an area
extended beyond 360 degrees to allow later filtering, run
grdraster 1
-R-4/364/-62/62
-I30
m -Gdata.grd
To obtain data for an oblique Mercator projection we need to extract more data
that is actually used. This is necessary because the output of
grdraster has edges defined by parallels and meridians, while the
oblique map in general does not. Hence, to get all the data from the ETOPO2
data needed to make a contour map for the region defined by its lower left and
upper right corners and the desired projection, use
grdraster ETOPO2
-R160/20/220/30
r
-Joc190/25.5/292/69/1
-Gdata.grd
To extract data from the 2 min Geoware relief blend and write it as binary
double precision xyz-triplets to standard output:
grdraster "2 min Geoware"
-R20/25/-10/5
-bo >!
triplets.b
SEE ALSO¶
gmtdefaults(1),
GMT(1),
grdsample(1),
grdfilter(1)
REFERENCES¶
Wessel, P., and W. H. F. Smith, 2011, The Generic Mapping Tools (GMT) version
4.5.7 Technical Reference & Cookbook, SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic Mapping
Tools Released, EOS Trans., AGU, 79 (47), p. 579.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools
Released, EOS Trans., AGU, 76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Mapping Tools
Released,
http://www.agu.org/eos_elec/95154e.html, Copyright 1995 by the
American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Display Data,
EOS Trans., AGU, 72 (41), p. 441.