gmtgravmag3d - Compute the gravity/magnetic effect of a body by the method of
-Tvvert_file OR -Tr|sraw_file [
-Cdensity ] [ -D ] [ -Ethickness ] [
-Fxy_file ] [ -Goutputgrid ] [
-Hf_dec/f_dip/m_int/m_dec/m_dip ] [
-Lz_observation ] [ -Sradius ] [
-Zlevel ] [ -V[level] ] [ -fg]
Note: No space is allowed between the option flag and the
gmtgravmag3d 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 with
- 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 grid file.
- Specify the region of interest.
- -Tpxyz_file[+m] -Tvvert_file OR
- 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 accurate
- 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
- Geographic grids (dimensions of longitude, latitude) will be converted to
meters via a "Flat Earth" approximation using the current
- -^ 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.
GRID DISTANCE UNITS¶
If the grid does not have meter as the horizontal unit, append
+uunit 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
2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe