Computes the Receiver Operating Characteristic curve for a point pattern or a fitted point process model.
roc(X, ...)# S3 method for ppp
roc(X, covariate, ..., high = TRUE)
Function value table (object of class "fv")
which can be plotted to show the ROC curve.
Point pattern (object of class "ppp" or "lpp")
or fitted point process model
(object of class "ppm", "kppm", "slrm"
or "lppm").
Spatial covariate. Either a function(x,y),
a pixel image (object of class "im"), or
one of the strings "x" or "y" indicating the
Cartesian coordinates.
Logical value indicating whether the threshold operation should favour high or low values of the covariate.
Arguments passed to as.mask controlling the
pixel resolution for calculations.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.
This command computes Receiver Operating
Characteristic curve. The area under the ROC is computed by auc.
For a point pattern X and a covariate Z, the
ROC is a plot showing the ability of the
covariate to separate the spatial domain
into areas of high and low density of points.
For each possible threshold \(z\), the algorithm calculates
the fraction \(a(z)\) of area in the study region where the
covariate takes a value greater than \(z\), and the
fraction \(b(z)\) of data points for which the covariate value
is greater than \(z\). The ROC is a plot of \(b(z)\) against
\(a(z)\) for all thresholds \(z\).
For a fitted point process model, the ROC shows the ability of the fitted model intensity to separate the spatial domain into areas of high and low density of points. The ROC is not a diagnostic for the goodness-of-fit of the model (Lobo et al, 2007).
(For spatial logistic regression models (class "slrm")
replace “intensity” by “probability of presence”
in the text above.)
Lobo, J.M., Jimenez-Valverde, A. and Real, R. (2007) AUC: a misleading measure of the performance of predictive distribution models. Global Ecology and Biogeography 17(2) 145--151.
Nam, B.-H. and D'Agostino, R. (2002) Discrimination index, the area under the ROC curve. Pages 267--279 in Huber-Carol, C., Balakrishnan, N., Nikulin, M.S. and Mesbah, M., Goodness-of-fit tests and model validity, Birkhauser, Basel.
auc