gmtgravmag3d - Compute the gravity/magnetic effect of a body by the method of
] [ -D
] [ -Ethickness
] [ -Goutputgrid
] [ -Sradius
] [ -V
] ] [ -fg
No space is allowed between the option flag and the associated
will compute the gravity or magnetic anomaly of a body
described by a set of triangles. The output can either be along a given set of
xy locations or on a grid. This method is not particularly fast but allows
computing the anomaly of arbitrarily complex shapes.
- Sets body density in SI. This option is mutually exclusive
- Sets parameters for computing a magnetic anomaly. Use
f_dec/ f_dip to set the geomagnetic declination/inclination
in degrees. m_int/m_dec/m_dip are the body magnetic
intensity declination and inclination.
- Provide locations where the anomaly will be computed. Note
this option is mutually exclusive with -G.
- Output the gravity or magnetic anomaly at nodes of this
- Specify the region of interest.
-Tvvert_file OR Tr|sraw_file
- Gives names of xyz (-Tpxyz_file[+m])
and vertex ( -Tvvert_file) files defining a close surface.
The file formats correspond to the output of the triangulate program. The
optional +m flag to -Tp instructs the program that the xyzm
file has four columns and that the fourth column contains the
magnetization intensity (plus signal), which needs not to be constant. In
this case the third argument of the -H option is ignored. A
raw format (selected by the -Tr option) is a file with N
rows (one per triangle) and 9 columns corresponding to the x,y,x
coordinates of each of the three vertex of each triangle. Alternatively,
the -Ts option indicates that the surface file is in the ASCII STL
(Stereo Lithographic) format. These two type of files are used to provide
a closed surface.
- -V[level] (more ...)
- Select verbosity level [c].
- give layer thickness in m [Default = 0 m]. Use this option
only when the triangles describe a non-closed surface and you want the
anomaly of a constant thickness layer.
- sets level of observation [Default = 0]. That is the height
(z) at which anomalies are computed.
- search radius in km. Triangle centroids that are further
away than radius from current output point will not be taken into
account. Use this option to speed up computation at expenses of a less
- level of reference plane [Default = 0]. Use this option
when the triangles describe a non-closed surface and the volume is defined
from each triangle and this reference level. An example will be the hater
depth to compute a Bouguer anomaly.
- Geographic grids (dimensions of longitude, latitude) will
be converted to meters via a "Flat Earth" approximation using
the current ellipsoid parameters.
- -^ or just -
- Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
- -+ 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 all options, then exits.
If the grid does not have meter as the horizontal unit, append
to the input file name to convert from the specified unit
to meter. If your grid is geographic, convert distances to meters by supplying
Suppose you ...
gmt, grdgravmag3d, talwani2d, talwani3d
Okabe, M., Analytical expressions for gravity anomalies due to polyhedral bodies
and translation into magnetic anomalies, Geophysics
, 44, (1979), p
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe