SpatialVx (version 1.0-3)

FeatureProps: Single Feature Properties

Description

Calculate properties for an identified feature.

Usage

FeatureProps(x, Im = NULL, which.props = c("centroid", "area", "axis", "intensity"),
    areafac = 1, q = c(0.25, 0.9), loc = NULL, ...)

Value

list object with components depending on the which.props argument. One or more of:

centroid

list with components x and y giving the centroid of the object.

area

numeric giving the area of the feature.

axis

list object of class FeatureAxis as returned by the same-named function.

Arguments

x

object of class “owin” containing a binary image matrix defining the feature.

Im

Matrix giving the original values of the field from which the feature was extracted. Only needed if the feature intensity is desired.

which.props

character vector giving one or more of “centroid”, “area”, “axis” and “intensity”. If “axis” is given, then a call to FeatureAxis is made.

areafac

numeric, in determining the lengths of the axes, they are multiplied by a factor of fac (e.g., if the grid points are k by k km each, then one could set this to k so that the resulting lengths are in terms of km rather than grid points.

q

numeric vector of values between 0 and 1 inclusive giving the quantiles for determining the intensity of the feature.

loc

optional argument giving a two-column matrix of grid locations for finding the centroid. If NULL, indices based on the dimension of x are used.

...

additional arguments to FeatureAxis.

Author

Eric Gilleland

Details

This function takes an owin image and returns several property values for that image, including: centroid, spatial area, major and minor axis angle/length, as well as the overall intensity of the field (cf., Davis et al., 2006a, b).

References

Davis, C. A., Brown, B. G. and Bullock, R. G. (2006a) Object-based verification of precipitation forecasts, Part I: Methodology and application to mesoscale rain areas. Mon. Wea. Rev., 134, 1772--1784.

Davis, C. A., Brown, B. G. and Bullock, R. G. (2006b) Object-based verification of precipitation forecasts, Part II: Application to convective rain systems. Mon. Wea. Rev., 134, 1785--1795.

Examples

data( "ExampleSpatialVxSet" )

x <- ExampleSpatialVxSet$vx

look <- disk2dsmooth(x,5)
u <- quantile(look,0.99)
sIx <- matrix(0, 100, 100)
sIx[ look > u] <- 1
look2 <- disjointer(sIx)[[1]]
look2 <- flipxy(look2)

FeatureProps(look2,
    which.props=c("centroid", "area", "axis"))