📄 gslib help page file formats.htm
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<H2>GSLIB Help Page: File Formats</H2></CENTER>
<DL>
<DT><IMG height=14 alt=o src="GSLIB Help Page File Formats.files/ball.red.gif"
width=14> <STRONG>Data Files:</STRONG>
<UL>
<LI>Although users are strongly encouraged to customize the programs,
workable main programs are useful starting points. The main programs read
and write data with a format similar to the menu-driven Geo-EAS package. The
format, described below, is a simple ASCII format with no data compression
or alphanumeric characters.
<P></P>
<LI>The data file format is a simplified Geo-EAS format, hence with no
allowance for the user to specify explicitly the input format. The data
values are always read with free format. The accessibility of the source
code allows this to be easily changed.
<LI>The following conventions are used by the ``simplified Geo-EAS format''
used by GSLIB data files:
<UL>
<LI>The first line in the file is taken as a title and is possibly
transferred to output files.
<LI>The second line should be a numerical value specifying the number of
numerical variables <B>nvar</B> in the data file.
<LI>The next <B>nvar</B> lines contain character identification labels and
additional text (optional) that describe each variable.
<LI>The following lines, from <B>nvar</B>+3 until the end of the file, are
considered as data points and must have <B>nvar</B> numerical values per
line. Missing values are typically considered as large negative or
positive numbers (e.g., less than -1.0e21 or greater than 1.0e21). The
number of data will be the number of lines in the file minus <B>nvar</B>+2
minus the number of missing values. The programs read numerical values and
<I>not</I> alphanumeric characters; alphanumeric variables may be
transformed to integers or the source code modified. </LI></UL><PRE>Clustered 140 primary and secondary data
5
Xlocation
Ylocation
Primary
Secondary
Declustering Weight
39.5 18.5 .06 .22 1.619
5.5 1.5 .06 .27 1.619
38.5 5.5 .08 .40 1.416
20.5 1.5 .09 .39 1.821
</PRE></LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help Page File Formats.files/ball.red.gif"
width=14> <STRONG>Grid Definition:</STRONG>
<UL>
<LI>Regular grids of data points or block values are often considered as
input or output. The conventions used throughout GSLIB are:
<UL>
<LI>The <I>X</I> axis is associated to the east direction. Grid node
indices <I>ix</I> increase from 1 to <I>nx</I> in the positive <I>x</I>
direction, i.e., to the east.
<LI>The <I>Y</I> axis is associated to the north direction. Grid node
indices <I>iy</I> increase from 1 to <I>ny</I> in the positive <I>y</I>
direction, i.e., to the north.
<LI>The <I>Z</I> axis is associated to the elevation. Grid node indices
<I>iz</I> increase from 1 to <I>nz</I> in the positive <I>z</I> direction,
i.e., upward. </LI></UL>
<LI>The user can associate these three axes to any coordinates system that
is appropriate for the problem at hand. For example, if the phenomenon being
studied is a stratigraphic unit, then some type of stratigraphic coordinates
relative to a marker horizon could make the most sense. The user must
perform the coordinate transformation; there is no allowance for rotation or
stratigraphic grids within the existing set of subroutines.
<LI>The coordinate system is established by specifying the coordinates at
the center of the first block (<I>xmn,ymn,zmn</I>), the number of
blocks/grid nodes (<I>nx,ny,nz</I>), and the size/spacing of the
blocks/nodes (<I>xsiz,ysiz,zsiz</I>).
<LI>Sometimes a special ordering is used to store a regular grid. This
avoids the requirement of storing node coordinates or grid indices. The
ordering is point by point to the east, then row by row to the north, and
finally level by level upward, i.e., <I>x</I> cycles fastest, then <I>y</I>,
and finally <I>z</I>. The index location of any particular node
<I>ix,iy,iz</I> can be located by:<BR>loc = (iz-1)*nx*ny + (iy-1)*nx + ix
<BR>Given the above one-dimensional index location of a node the three
coordinate indices can be calculated as<BR>iz = 1 + int( (loc-1)/(nx*ny) )
<BR>iy = 1 + int( (loc-(iz-1)*nx*ny)/nx ) <BR>ix = loc - (iz-1)*nx*ny -
(iy-1)*nx <BR></LI></UL>
<DT><IMG height=14 alt=o src="GSLIB Help Page File Formats.files/ball.red.gif"
width=14> <STRONG>Parameter Files:</STRONG>
<UL>
<LI>The default driver programs read the name of a parameter file from
standard input. If the parameter file is named for the program and has a
``.par'' extension, then simply keying a carriage return will be sufficient
(e.g., the program <TT>gam</TT> would automatically look for
<TT>gam.par</TT>). All of the program variables and names of input/output
files are contained in the parameter file. A typical parameter file:
<P><PRE> Parameters for GAM
******************
START OF PARAMETERS:
../data/true.dat \file with data
2 1 2 \ number of variables, column numbers
-1.0e21 1.0e21 \ trimming limits
gam.out \file for variogram output
1 \grid or realization number
50 0.5 1.0 \nx, xmn, xsiz
50 0.5 1.0 \ny, ymn, ysiz
1 0.5 1.0 \nz, zmn, zsiz
2 10 \number of directions, number of lags
1 0 0 \ixd(1),iyd(1),izd(1)
0 1 0 \ixd(2),iyd(2),izd(2)
1 \standardize sill? (0=no, 1=yes)
2 \number of variograms
1 1 1 \tail variable, head variable, variogram type
1 1 3 \tail variable, head variable, variogram type
</PRE>
<LI>The user can have as many lines of comments at the top of the file as
desired, but formatted input is started immediately after the characters
``START'' are found at the beginning of a line. Some in-line documentation
is available to supplement the detailed documentation provided in this
electronic help and the actual book. </LI></UL></DT></DL><IMG height=8 alt=---
src="GSLIB Help Page File Formats.files/line.blue.gif" width=652>
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