Description Usage Arguments Details Value Author(s) References See Also Examples
Calculate the shape index (Sindex) as described in AghaKouchak et al. (2011)
1 2 3 4 5 6 7 8 9 
x 
Default: m by n numeric matrix giving the field for which the shape index is to be calculated.

thresh 
numeric giving a threshold under which (and including, i.e., <=) all values are set to zero, and the shape index is calculated for the nonzero (positivevalued) gridpoints. 
loc 
(optional) mn by 2 numeric matrix giving the grid point locations. If NULL, the expanded grid with x=1:m and y=1:n is used. 
time.point 
numeric or character indicating which time point from the “SpatialVx” verification set to select for analysis. 
obs, model 
numeric indicating which observation/forecast model to select for the analysis. 
... 
Not used. 
The shape index introduced in AghaKouchak et al. (2011) is defined as
Sindex = Pmin/P,
where for n = the number of positivevalued grid points, Pmin = 4*sqrt(n) if floor(sqrt(n)) = sqrt(n), and Pmin = 2 * floor(2*sqrt(n)+1) otherwise. P is the permieter of the nonzero grid points. Range is 0 to 1. Values closer to 1 indicate shapes that are closer to circular.
numeric with named components:
Sindex 
the shape index 
Pmin,P 
the numerator and denominator (perimeter) that make the Sindex. 
For “SpatialVx” objects, the routine is applied to both the verification and forecast objects so that a tworow matrix is returned containing the above vectors for each field.
Eric Gilleland
AghaKouchak, A., Nasrohllahi, N., Li, J., Imam, B. and Sorooshian, S. (2011) Geometrical characterization of precipitation patterns. J. Hyrdometeorology, 12, 274–285, doi:10.1175/2010JHM1298.1.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24  # Recreate Fig. 7a from AghaKouchak et al. (2011).
tmp < matrix(0, 8, 8)
tmp[3,2:4] < 1
tmp[5,4:6] < 1
tmp[7,6:7] < 1
Sindex(tmp)
## Not run:
# Two separate areas with highly structured shapes, but far away from each other.
data( "pert000" )
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 = "ICP Perturbed Cases", obs.name = "pert000",
model.name = "pert006" )
plot( hold )
Sindex( hold )
## End(Not run)

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