v.qcount - Indices for quadrat counts of vector point lists.

       James Darrell McCauley
       when he was at: Agricultural Engineering Purdue University

       Modified for GRASS 5.0 by Eric G. Miller (2000-10-28)
       Modified for GRASS 5.7 by R. Blazek (2004-10-14)

v.qcount  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.

       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.
       Figure1:Realizationoftwo-dimensionalPoissonprocessesof50pointsontheunitsquareexhibiting(a)completespatialrandomness,(b)regularity,and(c)clustering.

       Various indices and statistics measure departure from CSR. The v.qcount function implements six different
       quadratcount  indices  that  are  described  in  Cressie  (1991; p. 590-591)[1] and in Ripley (1981; p.
       102-106)[2] and summarized in Table 1.
       Table1:IndicesforQuadratCountData.AdaptedfromCressie[1],thistableshowsthestatisticscomputedforthequadratsinFigure2.

       These indices are computed as follows: v.qcount chooses nquadrads circular quadrats of radius radius 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.
       Figure2:Randomlyplacedquadrats(n=100)with584samplepoints.

       The number of points is written as category to the output map (and not to an attribute table).

       vector, statistics, point pattern

       Timestamp not working for header part of counts output. (2000-10-28)

v.qcount  - Indices for quadrat counts of vector point lists.

       This  program  may  not  work  properly  with  lat-long  data.  It uses hypot() in two files: count.c and
       findquads.c.

Generalreferencesinclude:

       [1] Noel A. C. Cressie. StatisticsforSpatialData.   Wiley  Series  in  Probability  and  Mathematical
       Statistics. John Wiley & Sons, New York, NY, 1st edition, 1991.

       [2] Brian D. Ripley. SpatialStatistics.  John Wiley \& Sons, New York, NY, 1981.

       Referencestotheindicesinclude:

       [3]  R. A. Fisher, H. G. Thornton, and W. A. Mackenzie.  The accuracy of the plating method of estimating
       the density of bacterial populations.  AnnalsofAppliedBiology, 9:325-359, 1922.

       [4] F. N. David and P. G. Moore. Notes on  contagious  distributions  in  plant  populations.  AnnalsofBotany, 18:47-53, 1954.

       [5] J. B. Douglas.  Clustering and aggregation.  SankhyaB, 37:398-417, 1975.

       [6] M. Lloyd. Mean crowding.  JournalofAnimalEcology, 36:1-30, 1967.

       [7]  M.  Morista. Measuring the dispersion and analysis of distribution patterns. MemoiresoftheFacultyofScience,KyushuUniversity,SeriesE.Biology, 2:215-235, 1959.

       Amoredetailedbackgroundisgiveninthetutorial:

       [8] James Darrell McCauley 1993. Complete Spatial Randomness and Quadrat  Methods  -  GRASS  Tutorial  on
       v.qcount

v.random,v.distance,v.neighbors,v.perturb

       Available at: v.qcount source code (history)

       Accessed: Friday Apr 04 01:20:32 2025

       Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

       © 2003-2025 GRASS Development Team, GRASS GIS 8.4.1 Reference Manual

GRASS 8.4.1                                                                                     v.qcount(1grass)

v.qcountv.qcount--helpv.qcount  [-g]  input=name  [layer=string]   [output=name]  nquadrats=integerradius=float  [--overwrite]
       [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:-g
           Print results in shell script style

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:input=name[required]
           Name of input vector map
           Or data source for direct OGR access

       layer=string
           Layer number or name (’-1’ for all layers)
           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.
           Default: -1output=name
           Name for output quadrat centers map (number of points is written as category)

       nquadrats=integer[required]
           Number of quadrats

       radius=float[required]
           Quadrat radius