Diggle's Heather Data
The spatial mosaic of vegetation of the heather plant (Calluna vulgaris) recorded in a 10 by 20 metre sampling plot in Sweden.
A list with three entries, representing the same data at different spatial resolutions:
||original heather data, 100 by 200 pixels|
||current heather data, 256 by 512 pixels|
Each of these entries is an object of class
containing a binary pixel mask.
Notes on data
These data record the spatial mosaic of vegetation of the heather plant (Calluna vulgaris) in a 10 by 20 metre sampling plot near Jadraas, Sweden. They were recorded and first analysed by Diggle(1981).
heather contains three different versions of the data
that have been analysed by different writers over the decades.
Data as originally digitised by Diggle in 1983 at 100 by 200 pixels resolution (i.e. 10 pixels = 1 metre).
These data were entered by hand in the form of a run-length encoding (original file no longer available) and translated by a program into a 100 by 200 pixel binary image.
There are known to be some errors in the image which arise from errors in counting the run-length so that occasionally there will be an unexpected 'spike' on one single column.
A fine scale digitisation of the original map, prepared by CWI (Centre for Computer Science, Amsterdam, Netherlands) in 1994.
The original hand-drawn map was scanned by Adrian Baddeley Adrian.Baddeley@curtin.edu.au, and processed by Chris Jonker, Henk Heijmans and Adrian Baddeley Adrian.Baddeley@curtin.edu.au to yield a clean binary image of 778 by 1570 pixels resolution.
The version of the heather data currently supplied on Professor Diggle's website. This is a 256 by 512 pixel image. The method used to create this image is not stated.
History of analysis of data
The data were recorded, presented and analysed by Diggle (1983). He proposed a Boolean model consisting of discs of random size with centres generated by of a Poisson point process.
Renshaw and Ford (1983) reported that spectral analysis of the data suggested the presence of strong row and column effects. However, this may have been attributable to errors in the run-length encoding of the original data.
Hall (1985) and Hall (1988, pp 301-318) took a bootstrap approach.
Ripley (1988, pp. 121-122, 131-135] used opening and closing functions to argue that a Boolean model of discs is inappropriate.
Cressie (1991, pp. 763-770) tried a more general Boolean model.
Cressie, N.A.C. (1991) Statistics for Spatial Data. John Wiley and Sons, New York.
Diggle, P.J. (1981) Binary mosaics and the spatial pattern of heather. Biometrics 37, 531-539.
Hall, P. (1985) Resampling a coverage pattern. Stochastic Processes and their Applications 20 231-246.
Hall, P. (1988) An introduction to the theory of coverage processes. John Wiley and Sons, New York.
Renshaw, E. and Ford, E.D. (1983) The interpretation of process from pattern using two-dimensional spectral analysis: Methods and problems of interpretation. Applied Statistics 32 51-63.
Ripley, B.D. (1988) Statistical Inference for Spatial Processes. Cambridge University Press.