Model file: trapezod.m
Comments: The model file, trapezod.m, is an example of trapezohedron
model from Coggon (1976). This example shows how
model parameters are to be given. The variables are Ncor D number of corners of the model; Hintn D total intensity of
ambient magnetic induction, gamma; Hincl D inclination of
Hintn, degrees, downward from horizontal; DeclDdeclination
of Hintn, clockwise from north; Susc D magnetic volume susceptibility
in units SI, a dimensionlessnumberequal to ((c)ör ¡1),
where (c)ör D magnetic permeability of the model relative to
free space; Mstrength, Mincl, Mdecl D magnitude (gamma),
inclination and declination (degrees), respectively, of remnant
magnetic induction; Nf D number of faces; Fht D height of observation
plane above origin, meters; and dens D density of
model, g/cm3.
calgrvD1; % Change to zero if gravity field is not required
calmagD1; % Change to zero if magnetic field is not required
NcorD26; HintnD50000; HinclD50; DeclD0; SuscD0.01
MstrengthD0; MinclD0; MdeclD0;
Comments: Corner is an array of x, y, z coordinates of corners
in meters, one in each row, in a right-handed system with
x-axis northward, y-axis eastward, and z-axis downward. Corners
may be given in any order.
Corner D [100 0 0; 75¡75 0; 0 ¡100 0; ¡75 ¡75 0; ¡100 0 0;...
¡75 75 0; 0 100 0; 75 75 0; 75 0 ¡75; 60 ¡60 ¡60; 0 ¡75 ¡75;...
¡60 ¡60 ¡60; ¡75 0 ¡75; ¡60 60 ¡60; 0 75¡75; 60 60 ¡60;...
0 0¡100; 75 0 75; 60 ¡60 60; 0 ¡75 75; ¡60 ¡60 60; ¡75 0 75;...
¡60 60 60; 0 75 75; 60 60 60; 0 0 100];
fhtD200; densD10;
% Add fht to depths of all corners
Corner(:,3)DCorner(:,3)Cfht;
Comments: In each row of Face, the first number is the number
of corners forming a face; the following are row numbers of the
Corner array with coordinates of the corners which form that
face, seen in ccw order from outside the object. The faces may
have any orientation and may be given in any order, but all
faces must be included.
FaceDzeros([50,9]); % Initialize a sufficiently large array
Face(1,1:5)D[4 1 2 10 9]; Face(2,1:5)D[4 2 3 11 10];
Face(3,1:5)D[4 3 4 12 11]; Face(4,1:5)D[4 4 5 13 12];
Face(5,1:5)D[4 5 6 14 13]; Face(6,1:5)D[4 6 7 15 14];
Face(7,1:5)D[4 7 8 16 15]; Face(8,1:5)D[4 8 1 9 16];
Face(9,1:5)D[4 9 10 11 17]; Face(10,1:5)D[4 11 12 13 17];
Face(11,1:5)D[4 13 14 15 17]; Face(12,1:5)D[4 15 16 9 17];
Face(13,1:5)D[4 1 18 19 2]; Face(14,1:5)D[4 2 19 20 3];
Face(15,1:5)D[4 3 20 21 4]; Face(16,1:5)D[4 4 21 22 5];
Face(17,1:5)D[4 5 22 23 6]; Face(18,1:5)D[4 6 23 24 7];
Face(19,1:5)D[4 7 24 25 8]; Face(20,1:5)D[4 8 25 18 1];
Face(21,1:5)D[4 20 19 18 26]; Face(22,1:5)D[4 22 21 20 26];
Face(23,1:5)D[4 24 23 22 26]; Face(24,1:5)D[4 18 25 24 26];
Comments: Rectangular grid of stations for computing fields.
Profiles are along the x-axis (north-south direction). All values
are in meters.
s endD¡320; % Starting value of x; south end of profiles
stn spcng D 40; % Stepsize in north direction; stn interval
n endD 320; % Last x; maximum north coordinate
w endD 0; % y value for westernmost profile
prof spcngD1; % Profile spacing
e endD 0; % y value for easternmost profile