.TH v.qcount 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.qcount\fR\fR  \- Indices for quadrat counts of vector point lists.
.SH KEYWORDS
vector, statistics, point pattern
.SH SYNOPSIS
\fBv.qcount\fR
.br
\fBv.qcount \-\-help\fR
.br
\fBv.qcount\fR [\-\fBg\fR] \fBinput\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]   [\fBoutput\fR=\fIname\fR]  \fBnquadrats\fR=\fIinteger\fR \fBradius\fR=\fIfloat\fR  [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-g\fR" 4m
.br
Print results in shell script style
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector map
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name (\(cq\-1\(cq for all layers)
.br
A single vector map can be connected to multiple database tables. This number determines which table to use. When used with direct OGR access this is the layer name.
.br
Default: \fI\-1\fR
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output quadrat centers map (number of points is written as category)
.IP "\fBnquadrats\fR=\fIinteger\fR \fB[required]\fR" 4m
.br
Number of quadrats
.IP "\fBradius\fR=\fIfloat\fR \fB[required]\fR" 4m
.br
Quadrat radius
.SH DESCRIPTION
\fIv.qcount\fR computes six different quadrat count statistics that provide
a measure of how much an user defined point pattern departs from a complete
spatial random point pattern.
.PP
Points are distributed following a complete spatial randomness (CSR) pattern
if events are equally likely to occur anywhere within an area. There are two
types departure from a CSR: regularity and clustering. Figure 1 gives an example
of a complete random, regular and a clustered pattern.
.br
\fIFigure 1: Realization of two\-dimensional Poisson processes of 50 points on
the unit square exhibiting (a) complete spatial randomness, (b) regularity, and
(c) clustering.\fR
.PP
Various indices and statistics measure departure from CSR. The
\fIv.qcount\fR function implements six different \fIquadrat count\fR
indices that are described in Cressie (1991; p. 590\-591)[1] and in Ripley (1981;
p. 102\-106)[2] and summarized in Table 1.
.br
\fITable 1: Indices for Quadrat Count Data. Adapted from
Cressie [1], this table shows the statistics computed for the
quadrats in Figure 2.\fR
.PP
These indices are computed as follows: \fIv.qcount\fR chooses
\fBnquadrads\fR circular quadrats of radius \fBradius\fR such that they are
completely within the bounds of the current region and no two quadrats overlap.
The number of points falling within each quadrat are counted and indices are
calculated to estimate the departure of point locations from complete spatial
randomness. This is illustrated in Figure 2.
.br
\fIFigure 2: Randomly placed quadrats (n = 100) with 584 sample points.\fR
.PP
The number of points is written as category to the \fBoutput\fR map (and not
to an attribute table).
.SH NOTES
This program may not work properly with lat\-long data. It uses
\fIhypot()\fR in two files: \fIcount.c\fR and
\fIfindquads.c\fR.
.SH SEE ALSO
\fI
v.random,
v.distance,
v.neighbors,
v.perturb
\fR
.SH REFERENCES
\fBGeneral references include:\fR
.PP
[1] Noel A. C. Cressie. \fIStatistics for Spatial Data\fR.
Wiley Series in Probability and Mathematical Statistics. John Wiley
& Sons, New York, NY, 1st edition, 1991.
.PP
[2] Brian D. Ripley. \fISpatial Statistics\fR.
John Wiley \(rs& Sons, New York, NY, 1981.
.PP
\fBReferences to the indices include:\fR
.PP
[3] R. A. Fisher, H. G. Thornton, and W. A. Mackenzie.
The accuracy of the plating method of estimating the density of
bacterial populations.
\fIAnnals of Applied Biology\fR, 9:325\-359, 1922.
.PP
[4] F. N. David and P. G. Moore. Notes on contagious distributions in
plant populations. \fIAnnals of Botany\fR, 18:47\-53, 1954.
.PP
[5] J. B. Douglas.  Clustering and aggregation.
\fISankhya B\fR, 37:398\-417, 1975.
.PP
[6] M. Lloyd. Mean crowding.
\fIJournal of Animal Ecology\fR, 36:1\-30, 1967.
.PP
[7] M. Morista. Measuring the dispersion and analysis of distribution
patterns. \fIMemoires of the Faculty of Science, Kyushu University, Series E.
Biology\fR, 2:215\-235, 1959.
.PP
\fBA more detailed background is given in the tutorial:\fR
.PP
[8] James Darrell McCauley 1993. Complete Spatial Randomness and Quadrat Methods \-
GRASS Tutorial on v.qcount
.SH KNOWN ISSUES
Timestamp not working for header part of counts output. (2000\-10\-28)
.SH AUTHORS
James Darrell McCauley
.br
when he was at:
Agricultural Engineering
Purdue University
.PP
Modified for GRASS 5.0 by Eric G. Miller (2000\-10\-28)
.br
Modified for GRASS 5.7 by R. Blazek (2004\-10\-14)
.SH SOURCE CODE
.PP
Available at: v.qcount source code (history)
.PP
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Full index
.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual