GSLIB Help Page: GAMV
Variogram calculation with scattered data
datafl: the input data in a simplified Geo-EAS formatted file.
icolx, icoly and icolz: the columns for the x,
y, and z coordinates (any of the column numbers may be
set to zero if that coordinate is not present in the data, e.g., 2-D
data may be handled by setting icolz to 0)
nvar and ivar(1) \ldots ivar(nvar): the number of
variables and their column order in the data file.
tmin and tmax: all values, regardless of which variable,
strictly less than tmin and greater than or equal to tmax
outfl: the output variograms are written to a single output
file named outfl The output file contains the variograms
ordered by direction and then variogram type specified in the parameter
file (the directions cycle fastest then the variogram number). For
each variogram there is a one-line description and then nlag
lines each with the following:
lag number (increasing from 1 to nlag
average separation distance for the lag.
the semivariogram value (whatever type was specified).
number of pairs for the lag.
mean of the data contributing to the tail.
mean of the data contributing to the head.
the tail and head variances (for the correlogram).
nlag: the number of lags to compute (same for all directions).
xlag: the unit lag separation distance.
xltol: the lag tolerance. This could be one-half of
xlag or smaller to allow for data on a pseudo-regular grid.
If xltol is entered as negative or zero it will be reset to
xlag/2. A pair will report to multiple lags if xltol is
greater than one-half of xlag
ndir: the number of directions to consider. All these directions
are considered for all of the nvarg variograms specified below.
azm, atol, bandwh, dip, dtol, and bandwd: the azimuth
angle, the half window azimuth tolerance, the azimuth bandwidth, the dip
angle, the half window dip tolerance, and the dip bandwidth. The
azimuth is measured in degrees clockwise from north, e.g., azm=0
is north, azm=90 is east, and azm=135 is south-east.
The dip angle is measured in negative degrees down from horizontal
i.e., dip=0 is horizontal, dip=-90 is vertical downward,
and dip=-45 is dipping down at 45 degrees. bandwh is the
horizontal ``bandwidth'' or maximum acceptable horizontal deviation
from the direction vector.
bandwd is the vertical ``bandwidth'' or maximum acceptable
deviation perpendicular to the dip direction in the vertical plane.
standardize: if set to 1, the semivariogram values will be
divided by the variance
nvarg: the number of variograms to compute.
The "variogram type" is specified by an integer
ivtail, ivhead and ivtype: for each of the nvarg
variograms one must specify which variables should be used for the
tail and head and which type of variogram is to be computed.
For direct variograms the ivtail array is identical to
the ivhead array. Cross variograms are computed by having the
tail variable different from the head variable.
cut: whenever the ivtype is set to 9 or 10, i.e., asking
for an indicator variogram, then a cutoff must be specified immediately
after the ivtype parameter on the same line in the input file.
Note that if an indicator variogram is
being computed then the cutoff/category applies to variable
ivtail(i) in the input file (although the ivhead(i)
variable is not used it must be present in the file to maintain
consistency with the other variogram types).