📄 gslib help varmap.htm
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<H2>GSLIB Help Page: VARMAP</H2></CENTER>
<DL>
<DT><IMG height=14 alt=o src="GSLIB Help VARMAP.files/ball.red.gif" width=14>
<STRONG>Description:</STRONG>
<UL>
<LI>Variograms are traditionally presented as 1-D curves as a function of
the distance <B>h</B> along a particular direction. It is often useful to
have a global view of the variogram values in all directions. The variogram
map is a 2-D plot of the sample semivariogram for all experimentally
available separation vectors </LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help VARMAP.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>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>igrid:</B> set to 1 if the data are on a regular grid and set to 0 if
the data are irregularly spaced.
<LI><B>nx, ny</B> and <B>nz:</B> the number of nodes in the <I>x</I>,
<I>y</I>, and <I>z</I> coordinate directions (used if <B>igrid</B> is set to
1). Any of the numbers may be set to one if that coordinate is not present
in the data, e.g., 2-D data may be handled by setting <B>nz</B> to 1.
<LI><B>xsiz, ysiz</B> and <B>zsiz:</B> the separation distance between the
nodes in the <I>x</I>, <I>y</I>, and <I>z</I> coordinate directions (used if
<B>igrid</B> is set to 1).
<LI><B>icolx, icoly</B> and <B>icolz:</B> the columns for the <I>x</I>,
<I>y</I>, and <I>z</I> coordinates (used if <B>igrid</B> is set to 0). 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>outfl:</B> the output file for the variogram maps/volumes are written
to a single output file named <B>outfl</B> This file contains each variogram
map/volume written sequentially as a grid with the <I>x</I> direction
cycling fastest, then <I>y</I>, then <I>z</I>.
<LI><B>nxlag, nylag</B> and <B>nzlag:</B> the number of lags to compute in
the <I>X, Y</I> and <I>Z</I> directions
<LI><B>dxlag, dylag</B> and <B>dzlag:</B> the lag tolerances or ``cell
sizes'' in the <I>X, Y</I> and <I>Z</I> directions
<LI><B>minpairs:</B> the minimum number of pairs needed to define a
variogram value (set to missing if fewer than <B>minpairs</B> is found).
<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 <I>nvarg</I>
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><IMG height=14 alt=o src="GSLIB Help VARMAP.files/ball.red.gif" width=14>
<STRONG>Application notes:</STRONG>
<UL>
<LI>Directions of anisotropy are usually evident from a variogram map.
Visualization of a variogram volume is best done using a graphical routine
that allows continuous sectioning of the volume along any of
</LI></UL></DT></DL><IMG height=8 alt=---
src="GSLIB Help VARMAP.files/line.blue.gif" width=652>
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