📄 gslib help gamv.htm
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<STRONG>Description:</STRONG>
<UL>
<LI>Variogram calculation with scattered data </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help GAMV.files/ball.red.gif" width=14>
<STRONG>Parameters:</STRONG>
<UL>
<LI><B>datafl:</B> the input data in a simplified Geo-EAS formatted file.
<LI><B>icolx, icoly</B> and <B>icolz:</B> the columns for the <I>x</I>,
<I>y</I>, and <I>z</I> 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 <B>icolz</B> to 0)
<LI><B>nvar</B> and <B>ivar(1) \ldots ivar(nvar):</B> the number of
variables and their column order in the data file.
<LI><B>tmin</B> and <B>tmax:</B> all values, regardless of which variable,
strictly less than <B>tmin</B> and greater than or equal to <B>tmax</B> are
ignored.
<LI><B>outfl:</B> the output variograms are written to a single output file
named <B>outfl</B> 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 <B>nlag</B> lines each with the
following:
<UL>
<LI>lag number (increasing from 1 to <B>nlag</B>
<LI>average separation distance for the lag.
<LI>the <I>semivariogram</I> value (whatever type was specified).
<LI>number of pairs for the lag.
<LI>mean of the data contributing to the tail.
<LI>mean of the data contributing to the head.
<LI>the tail and head variances (for the correlogram). </LI></UL>
<LI><B>nlag:</B> the number of lags to compute (same for all directions).
<LI><B>xlag:</B> the unit lag separation distance.
<LI><B>xltol:</B> the lag tolerance. This could be one-half of <B>xlag</B>
or smaller to allow for data on a pseudo-regular grid. If <B>xltol</B> is
entered as negative or zero it will be reset to <B>xlag</B>/2. A pair will
report to multiple lags if <B>xltol</B> is greater than one-half of
<B>xlag</B>
<LI><B>ndir:</B> the number of directions to consider. All these directions
are considered for all of the <B>nvarg</B> variograms specified below.
<LI><B>azm, atol, bandwh, dip, dtol,</B> and <B>bandwd:</B> 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., <B>azm=0</B> is north,
<B>azm=90</B> is east, and <B>azm=135</B> is south-east. The dip angle is
measured in negative degrees down from horizontal i.e., <B>dip=0</B> is
horizontal, <B>dip=-90</B> is vertical downward, and <B>dip=-45</B> is
dipping down at 45 degrees. <B>bandwh</B> is the horizontal ``bandwidth'' or
maximum acceptable horizontal deviation from the direction vector.
<B>bandwd</B> is the vertical ``bandwidth'' or maximum acceptable deviation
perpendicular to the dip direction in the vertical plane.
<LI><B>standardize:</B> if set to 1, the semivariogram values will be
divided by the variance
<LI><B>nvarg:</B> the number of variograms to compute.
<LI>The "variogram type" is specified by an <A
href="http://www.gslib.com/gslib_help/vtype.html">integer code</A>
<LI><B>ivtail, ivhead</B> and <B>ivtype:</B> for each of the <B>nvarg</B>
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 <B>ivtail</B> array is identical to the <B>ivhead</B> array. Cross
variograms are computed by having the tail variable different from the head
variable.
<LI><B>cut:</B> whenever the <B>ivtype</B> is set to 9 or 10, i.e., asking
for an indicator variogram, then a cutoff must be specified immediately
after the <B>ivtype</B> 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 <B>ivtail(i)</B> in the input file (although the
<B>ivhead(i)</B> variable is not used it must be present in the file to
maintain consistency with the other variogram types). </LI></UL></DT></DL><IMG
height=8 alt=--- src="GSLIB Help GAMV.files/line.blue.gif" width=652>
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