This function gives access to a sampling scenario which is based on the mapping of radioactivity and the calculation of a radionuclide inventory within a water body. (A `firth' is a Scottish term for a long, narrow indentation of the sea coast at the mouth of a river.) Interest lies in nuclides which, on release into a water body, attach (absorb) to sediment in a manner which depends on the sediment particle size. Cobalt-60 and caesium-137 are examples of nuclides which exhibit this behaviour. In this sampling scenario, the map of sediment type is used to define regions of different particle size from which the sediment samples will be collected by grabs from a boat. The presence of strata therefore has to be considered, as the different types of material on the sea bed may affect the mean values of the measurements taken.
The function displays a map and gives graphical control over a variety of sampling strategies. Once the user has drawn a sample, some simple predictions over the whole firth can be produced. The geoR package is used to construct these predictions.
rp.firth(hscale = NA, col.palette = rev(heat.colors(40)), col.se = "blue", file = NA,
parameters = NA)a scaling parameter which expands (>1) or contracts (<1) the size of the plot within the panel. This can be useful for projection onto a screen, for example. The vertical scale is set to the same value as the horizontal scale, to ensure that the plot is square. The default values are 1 on Unix platforms and 1.4 on Windows platforms.
the colour palette used to display the predicted and true spatial surfaces.
the colour used to draw the standard error contours on the predicted surface.
the name of a file to which the sampled data will be written.
a list which can be used to change the parameters which control the simulated measurement data.
Nothing in returned.
The use of the function is discussed in detail in the paper by Bowman et al. (2008) referenced below.
Once the data have been sampled, a data file may be saved for further analysis external to the rp.firth function, using the file argument. A convenient way of saving to the current working directory, for example to a file named firth.dmp, is to set the file argument to file.path(getwd(), "firth.dmp"). The load function can then be applied to the saved file to create an object called mururoa.data, which is a three-column matrix with the x and y locations in columns 1 and 2 and the observed values in column 3.
Bowman, A.W., Crawford, E., Alexander, G. Gibson and Bowman, R.W. (2007). rpanel: Simple interactive controls for R functions using the tcltk package. Journal of Statistical Software, 17, issue 9.
Bowman, A.W., Gibson, I., Scott, E.M. and Crawford, E. (2008). Interactive Teaching Tools for Spatial Sampling. Journal of Statistical Software, 36, 13, 1--17.
# NOT RUN {
rp.firth()
# }
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