GSLIB Help Page: COKB3D

Description:

A cokriging program for a points or blocks on a regular grid.

Parameters:

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

nvar: the number of variables (primary plus all secondary). For
example, nvar=2 if there is only one secondary variable.

icolx, icoly, icolz and icolvr(): the columns for the
x, y
and z coordinates, the primary variable to be kriged, and all
secondary variables.

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

coloc: set to 1 if performing colocated cokriging with a gridded
secondary variable, otherwise set to 0.

secfl: if colocated cokriging, the file with the gridded
secondary variable.

icolsec: if colocated cokriging, the column number for the
secondary variable in secfl

idbg: an integer debugging level between 0 and 3. The higher
the debugging level the more output. Normally
level 0 or 1 should be chosen.

dbgfl: the debugging output is written to this file.

outfl: the output grid is written to this file. The output
file will contain both the kriging estimate and the kriging variance
for all points/blocks. The output grid cycles fastest on x
then y then z

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 set to 1 then
point cokriging is performed.

ndmin, ndmaxp and ndmaxs: the minimum and maximum number of
primary data, and the maximum number of secondary data (regardless of
which secondary variable) to use for kriging a block.

search radii for primary data

search radii for secondary data (same for all types)

the angles defining the common orientation of the search ellipsoids
for primary and secondary data

ktype: the kriging type must be specified: 0 = simple cokriging,
1 = standardized ordinary cokriging with recentered variables and a
single unbiasedness constraint; 2 = traditional ordinary cokriging.

mean(): the mean of the primary and all secondary variables are
required input if either simple cokriging or standardized ordinary
cokriging are used. The program calculates the data residuals from
these means.
The direct and cross variograms may be specified in any order; they are
specified according to the variable number Variable ``1'' is
the primary (regardless of its column ordering in the input data files)
and the secondary variables are numbered from ``2'' depending on their
ordered specification in icolvr() It is unnecessary to specify
the j to i cross variogram if the i to j
cross variogram has been specified; the cross variogram is expected to
be symmetric (as from theory). For each i to j
variogram the following are required:

nst and c0: the number of variogram structures and the
isotropic 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 (the power model is not allowed); 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 construction of the cokriging matrix requires the linear model of
coregionalization. The input variogram parameters are checked for
positive definiteness. The power model is not allowed.

A specific search is done for secondary data (same for all secondary)
allowing the option of collocated cokriging.

A cokriging program for scattered points and cross validation is not
provided; programs cokb3d and kt3d could be combined
for this purpose.