gmtgravmag3d(1gmt)
NAME
gmtgravmag3d - Compute the gravity/magnetic effect of a body by the method of Okabe
SYNOPSIS
gmtgravmag3d -Tpxyz_file[+m] -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 associated arguments.
DESCRIPTION
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.
REQUIRED ARGUMENTS
-Cdensity
Sets body density in SI. This option is mutually exclusive with
-H.
-Hf_dec/f_dip/m_int/m_dec/m_dip
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.
-Fxy_file
Provide locations where the anomaly will be computed. Note this
option is mutually exclusive with -G.
-Goutgrid
Output the gravity or magnetic anomaly at nodes of this grid
file.
-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.
-Tpxyz_file[+m] -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
-Td 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.
OPTIONAL ARGUMENTS
-V[level] (more ...)
Select verbosity level [c].
-E[thickness]
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.
-L[z_observation]
sets level of observation [Default = 0]. That is the height (z)
at which anomalies are computed.
-Sradius
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 result.
-Z[level]
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.
-fg 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 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.
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 -fg instead.
EXAMPLES
Suppose you ...
gmt gmtgravmag3d ...
SEE ALSO
gmt, grdgravmag3d, talwani2d, talwani3d
REFERENCE
Okabe, M., Analytical expressions for gravity anomalies due to polyhedral bodies and translation into magnetic anomalies, Geophysics, 44, (1979), p 730-741.
COPYRIGHT
2016, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
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