Connectivity Index
Description
Calculate the connectivity index of an image.
Usage
1 2 3 4 5 6 7 8 
Arguments
x 
Default: m by n numeric matrix giving the field for which the shape index is to be calculated.

thresh 
Set values under (strictly less than) this threshold to zero, and calculate the connectivity index for the resulting image. If NULL, no threshold is applied. 
connect.method 
character string giving the 
time.point 
numeric or character indicating which time point from the “SpatialVx” verification set to select for analysis. 
model 
numeric indicating which forecast model to select for the analysis. 
... 
Not used. 
Details
The connectivity index is introduced in AghaKouchak et al. (2011), and is designed to automaticlaly determine how connected an image is. It is defined by
Cindex = 1  (NC  1)/(sqrt(NP) + NC),
where 0 <= Cindex <= 1 is the connectivity index (values close to zero are less connected, and values close to 1 are more connected), NP is the number of nonzero pixels, and NC is the number of isolated clusters.
The function connected
from package spatstat is used to identify the number of isolated clusters.
Value
numeric giving the connectivity index.
Author(s)
Eric Gilleland
References
AghaKouchak, A., Nasrollahi, N., Li, J., Imam, B. and Sorooshian, S. (2011) Geometrical characterization of precipitation patterns. J. Hydrometerology, 12, 274–285, doi:10.1175/2010JHM1298.1.
See Also
connected
, as.im
, Sindex
, Aindex
Examples
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21  data(geom000)
Cindex(geom000)
data(pert000)
Cindex(pert000)
## Not run:
# Two separate areas with highly structured shapes, but far away from each other.
data(pert006)
data(ICPg240Locs)
hold < make.SpatialVx(pert000, pert006, loc=ICPg240Locs,
projection=TRUE, map=TRUE, loc.byrow = TRUE,
field.type="Precipitation", units="mm/h",
data.name=c("ICP Perturbed Cases", "pert000", "pert006"))
plot(hold, set.pw=TRUE)
Cindex(hold)
## End(Not run)

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