R: Plot Pixel Image on Linear Network

plot.linim {spatstat.linnet} | R Documentation

## Plot Pixel Image on Linear Network

### Description

Given a pixel image on a linear network, the pixel values are displayed either as colours or as line widths.

### Usage

    ## S3 method for class 'linim'
    plot(x, ..., style = c("colour", "width"),
                 scale, adjust = 1, fatten = 0,
                 negative.args = list(col=2),
                 legend=TRUE,
                 leg.side=c("right", "left", "bottom", "top"),
                 leg.sep=0.1,
                 leg.wid=0.1,
                 leg.args=list(),
                 leg.scale=1,
                 zlim,
                 box=FALSE,
                 do.plot=TRUE)

### Arguments

`x` | The pixel image to be plotted. An object of class `"linim"`.
`...` | Extra graphical parameters, passed to `plot.im` if `style="colour"`, or to `polygon` if `style="width"`.
`style` | Character string (partially matched) specifying the type of plot. See Details.
`scale` | Physical scale factor for representing the pixel values as line widths.
`adjust` | Adjustment factor for the conversion of pixel value to line width, when `style="width"`.
`fatten` | Distance by which the line segments should be thickened, when `style="colour"`.
`negative.args` | A list of arguments to be passed to `polygon` specifying how to plot negative values of `x` when `style="width"`.
`legend` | Logical value indicating whether to plot a legend (colour ribbon or scale bar).
`leg.side` | Character string (partially matched) indicating where to display the legend relative to the main image.
`leg.sep` | Factor controlling the space between the legend and the image.
`leg.wid` | Factor controlling the width of the legend.
`leg.scale` | Rescaling factor for annotations on the legend. The values on the numerical scale printed beside the legend will be multiplied by this rescaling factor.
`leg.args` | List of additional arguments passed to `image.default`, `axis` or `text.default` to control the display of the legend. These may override the `...` arguments.
`zlim` | The range of numerical values that should be mapped. A numeric vector of length 2. Defaults to the range of values of `x`.
`box` | Logical value indicating whether to draw a bounding box.
`do.plot` | Logical value indicating whether to actually perform the plot.

### Details

This is the `plot` method for objects of class `"linim"`. Such an object represents a pixel image defined on a linear network.

If `style="colour"` (the default) then the pixel values of `x` are plotted as colours, using `plot.im`. The mapping from pixel values to colours is determined by any additional arguments `...` which are passed to `plot.im`.

If `style="width"` then the pixel values of `x` are used to determine the widths of thick lines centred on the line segments of the linear network. The mapping from pixel values to line widths is determined by the arguments `scale` and `adjust`. The plotting of colours and borders of the lines is controlled by the additional arguments `...` which are passed to `polygon`. A different set of colours and borders can be assigned to negative pixel values by passing a list of arguments in `negative.args` as shown in the Examples.

A legend is displayed alongside the plot if `legend=TRUE` (the default). The legend displays the relationship between pixel values and colours (if `style="colour"`) or between pixel values and line widths (if `style="width"`).

The plotting of the legend itself is controlled by the arguments `leg.side`, `leg.sep`, `leg.wid`, `leg.scale` and the list of arguments `leg.args`, which are described above. If `style="colour"`, these arguments are mapped to the arguments `ribside`, `ribsep`, `ribwid`, `ribscale` and `ribargs` respectively, which are passed to `plot.im`.

### Value

If `style="colour"`, the result is an object of class `"colourmap"` specifying the colour map used. If `style="width"`, the result is a numeric value `v` giving the physical scale: one unit of pixel value is represented as `v` physical units on the plot.

The result also has an attribute `"bbox"` giving a bounding box for the plot. The bounding box includes the ribbon or scale bar, if present, but not the main title.

### Thin lines

When `style="colour"` it often appears that the lines are drawn too thin. This occurs because `x` is a pixel image, in which the only pixels that have a defined value are those which lie directly over the network. To make the lines appear thicker in the plot, use the argument `fatten`. The domain of the image will be expanded by a distance equal to `fatten/2` in every direction using `dilation.owin`; the pixel values will be extrapolated to this expanded domain using `nearestValue`. This may improve the visual appearance of the plot.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

### References

Ang, Q.W., Baddeley, A. and Nair, G. (2012) Geometrically corrected second-order analysis of events on a linear network, with applications to ecology and criminology. Scandinavian Journal of Statistics 39, 591–617.

### See Also

`linim`, `plot.im`, `polygon`

### Examples

      X <- linfun(function(x,y,seg,tp){y^2+x}, simplenet)
      X <- as.linim(X)

      plot(X, main="Colour represents function value")
      plot(X, fatten=0.02, main="fattened")

      plot(X, style="width", main="Width proportional to function value")

      # signed values
      f <- linfun(function(x,y,seg,tp){y-x}, simplenet)
      plot(f, style="w", main="Negative values in red")

      plot(f, style="w", negative.args=list(density=10),
           main="Negative values are hatched")

[Package spatstat.linnet version 2.3-1 Index]