GSLIB Help Page: KT3D

Description:

The program kt3d provides a fairly advanced 3D kriging program
for points or blocks by simple kriging (SK), ordinary kriging (OK), or
kriging with a polynomial trend model (KT) with up to nine monomial
terms. The program works in 2D and is faster than kb2d if
there are many data. One of the features that makes this program
fairly fast is the super block search.

Parameters:

datafl: the input data in a simplified GeoEAS formatted file.

icolx, icoly, icolz, icolvr and icolsec: the columns for
the x, y, and z coordinates, the variable to be estimated,
and the external drift variable (or nonstationary mean).

tmin and tmax: all values strictly less than tmin
and greater than or equal to tmax are ignored.

option: set to 0 for kriging a grid of points or blocks, to 1 for
cross validation with the data in datafl and to 2 for
jackknifing with data in following file.

jackfl: file with locations to perform estimation (jackknife
option).

icolx, icoly, icolz, icolvr and icolsec: the columns for
the x, y, and z coordinates, the variable, and the
secondary variable in jackfl

idbg: an integer debugging level between 0 and 3. The higher
the debugging level the more output. The
normal levels are 0 and 1 which summarize the results. Levels 2 and
3 provide all the kriging matrices and data used for the estimation
of every point/block. It is recommended that a high debugging level
not be used with a large grid.

dbgfl: the debugging output is written to this file.

outfl: the output grid is written to this file. The output
contains the estimate and the kriging variance for
every point/block on the grid, cycling fastest on x then y
and finally z Unestimated points are flagged with a large
negative number (999.). The parameter UNEST, in the source code, can
be changed if a different number is preferred.

nx, xmn, xsiz: definition of the grid system (x axis).

ny, ymn, ysiz: definition of the grid system (y axis).

nz, zmn, zsiz: definition of the grid system (z axis).

nxdis, nydis and nzdis: the number of discretization
points for a block. If nxdis, nydis and nzdis are all
set to 1 then point kriging is performed.

ndmin and ndmax: the minimum and maximum number of data
points to use for kriging a block.

noct: the maximum number to retain from an octant (an octant
search is not used if noct=0

radius_hmax radius_hmin and radius_vert
the search radii in the maximum horizontal direction, minimum
horizontal direction, and vertical direction (see angles below).

sang1, sang2 and sang3: the angle parameters that
describe the orientation of the search ellipsoid. See the discussion
on anisotropy specification associated with Figure II.4.

ikrige and skmean: if ikrige is set to 0 then
stationary simple kriging with (skmean) will be performed, if
ikrige is set to 1 then ordinary kriging will be performed, if
ikrige is set to 2 then nonstationary simple kriging with means
taken from secfile will be performed, and if ikrige is set
to 3 then kriging with an external drift will be performed. Note that
power law variogram models (it=4) are not allowed with simple
kriging.

idrif(i),i=1...9: indicators for those drift terms to be included
in the trend model. idrif(i) is set to 1 if the drift term
number i
should be included, and is set to zero if not. The nine drift terms
correspond to the following:
 i = 1 linear drift in x
 i = 2 linear drift in y
 i = 3 linear drift in z
 i = 4 quadratic drift in x
 i = 5 quadratic drift in y
 i = 6 quadratic drift in z
 i = 7 cross quadratic drift in xy
 i = 8 cross quadratic drift in xz
 i = 9 cross quadratic drift in yz

itrend: indicator of whether to estimate the trend
(itrend =1) or the variable (itrend =0). The trend may be
kriged with ordinary kriging (all idrif(i) values set to 0) or
with any combination of trend kriging (some idrif(i) terms set
to 1).

secfl: a file for the gridded external drift variable. The
external drift variable is needed at all grid locations to be
estimated. The origin of the grid network, the number of nodes, and
the spacing of the grid nodes should be exactly the same as the grid
being kriged in kt3d This variable is used only if
ikrige=2 or 3.

iseccol: the column number in secfl for the gridded
secondary variable. This variable is used if ikrige=2 or 3.

nst and c0: the number of variogram structures and the
nugget constant. The nugget constant does not count as a structure.

For each of the nst nested structures one must define it,
the type of structure; cc, the c
parameter; ang1,ang2,ang3, the angles defining the geometric
anisotropy; aa_hmax, the maximum horizontal
range; aa_hmin, the minimum horizontal range; and
aa_vert, the vertical range.

Application notes:

The program is set up so that a novice programmer can make changes to
the form of the polynomial drift. The external drift concept has been
incorporated, adding an additional unbiasedness constraint to the
ordinary kriging system. When using an external drift,
it is necessary to know the value of the drift variable at all data
locations and all the locations that will be estimated (i.e., all grid
nodes).

The program also allows simple kriging with nonstationary means read
from an input file. The nonstationary means must be known at all
data locations and all locations to be estimated.