grdseamount - Compute synthetic seamount (Gaussian or cone, circular or
grdseamount [ intable ]
-Rregion [ -A[out/in] ] [
-Cc|d|g|p ] [ -D[unit] ] [
-E ] [ -F[flattening] ] [ -Ggrdfile ] [
-L[cut] ] [ -Mlist ] [ -Nnorm ] [
-Qbmode/qmode ] [ -Sscale ] [
] [ -Zlevel ] [ -V[level] ] [ -bibinary ] [
-fg ] [ -iflags ] [ -r ]
Note: No space is allowed between the option flag and the
grdseamount will compute the combined shape of multiple synthetic
seamounts given their individual shape parameters. We read a list with
seamount locations and sizes and can evaluate either Gaussian, parabolic,
conical, or disc shapes, which may be circular or elliptical, and optionally
truncated. Various scaling options are available to modify the result,
including an option to add in a background depth (more complicated backgrounds
may be added via grdmath). The input must contain lon,
lat, radius, height for each seamount. For elliptical
features (-E) we expect lon, lat, azimuth,
semi-major, semi-minor, height instead. If flattening is
specified (-F) with no value appended then a final column with
flattening is expected (cannot be used for plateaus). For temporal evolution
of topography the -T option may be used, in which case the data file
must have two final columns with the start and stop time of seamount
construction. In this case you may choose to write out a cumulative shape or
just the increments produced by each time step (see -Q).
- 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 s to
indicate arc seconds. If one of the units e, f, k,
M, n or u is appended instead, the increment is
assumed to be given in meter, foot, km, Mile, nautical mile or US survey
foot, respectively, and will be converted to the equivalent degrees
longitude at the middle latitude of the region (the conversion depends on
PROJ_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 App-file-formats for details. Note: if
-Rgrdfile is used then the grid spacing has already been
initialized; use -I to override the values.
- Specify the region of interest.
- Build a mask grid, append outside/inside values [1/NaN]. Here, height is
ignored and -L, -N and -Z are disallowed
- Select shape function: choose among c (cone), d (disc),
g (Gaussian) and p (parabolic) shape [Default is
- Append the unit used for horizontal distances in the input file (see
UNITS). Does not apply for geographic data (-fg) which we convert
- Elliptical data format [Default is Circular]. Read lon, lat, azimuth,
major, minor, height (m) for each seamount.
- Seamounts are to be truncated to guyots. Append flattening,
otherwise we expect to find it in last input column [no truncation].
Ignored if used with -Cd.
- Specify the name of the output grid file; see GRID FILE FORMATS below). If
-T is set then grdfile must be a filename template that
contains a floating point format (C syntax). If the filename template also
contains either %s (for unit name) or %c (for unit letter) then we use the
corresponding time (in units specified in -T) to generate the
individual file names, otherwise we use time in years with no unit.
- List area, volume, and mean height for each seamount; NO grid is created.
Optionally, append the noise-floor cutoff level below which we ignore area
and volume .
- Write the names of all grids that were created to the text file
list. Requires -T.
- Normalize grid so maximum grid height equals norm.
- Only to be used in conjunction with -T. Append two different modes
settings: The bmode determines how we construct the surface.
Specify c for cumulative volume through time, or i for
incremental volume added for each time slice. The qmode determines
the volume flux curve. Give g for a Gaussian volume flux history or
l for a linear volume flux history between the start and stop times
of each feature.
- Sets optional scale factor for radii .
- Specify t0, t1, and time increment (dt) for sequence
of calculations [Default is one step, with no time dependency]. For a
single specific time, just give start time t0. The unit is years;
append k for kyr and M for Myr. For a logarithmic time
scale, append +l and specify n steps instead of dt.
Alternatively, give a file with the desired times in the first column
(these times may have individual units appended, otherwise we assume
year). Note that the grid for t0 (if a range is given) is not
written as it is zero and marks the start of the building history.
- Set the background depth .
- -bi[ncols][t] (more ...)
- Select native binary input. [Default is 4 input columns].
- Geographic grids (dimensions of longitude, latitude) will be converted to
km via a "Flat Earth" approximation using the current ellipsoid
- Skip or produce header record(s). Not used with binary data.
- Select input columns (0 is first column).
- -V[level] (more ...)
- Select verbosity level [c].
- -r (more ...)
- Set pixel node registration [gridline].
- -:[i|o] (more ...)
- Swap 1st and 2nd column on input and/or output.
- -^ or just -
- Print a short message about the syntax of the command, then exits (NOTE:
on Windows use just -).
- -+ or just +
- Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.
- -? or no arguments
- Print a complete usage (help) message, including the explanation of
options, then exits.
For map distance unit, append unit d for arc degree, m for
arc minute, and s for arc second, or e for meter [Default],
f for foot, k for km, M for statute mile, n for
nautical mile, and u for US survey foot. By default we compute such
distances using a spherical approximation with great circles. Prepend -
to a distance (or the unit is no distance is given) to perform "Flat
Earth" calculations (quicker but less accurate) or prepend + to
perform exact geodesic calculations (slower but more accurate).
To compute the incremental loads from two elliptical, truncated Gaussian
seamounts being constructed from 3 Ma to 2 Ma and 2.8 M to 1.9 Ma using a
linear volumetric production rate, and output an incremental grid every 0.1
Myr from 3 Ma to 1.9 Ma, we can try:
cat << EOF > t.txt
#lon lat azimuth, semi-major, semi-minor, height tstart tend
0 0 -20 120 60 5000 3.0M 2M
50 80 -40 110 50 4000 2.8M 21.9M
gmt grdseamount -Rk-1024/1022/-1122/924 -I2000 -Gsmt_%3.1f_%s.nc t.txt -T3M/1.9M/0.1M -Qi/l -Dk -E -F0.2 -Cg -Ml.lis
gmt.conf, gmt, grdmath, gravfft, gmtflexure
2016, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe