Recovering information from existing lattice plots.
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If positive, the maximum number of points to locate. If negative (default), unlimited.
The unit to use when reporting located points, by
The correction to apply if the plot has locally scaled axes. See Note below.
Additional arguments, passed on to related functions.
These may be subject to revision, but are currently:
getXY is an interactive function which returns
the locations of points on a plot selected using the
mouse (left click to select points; right click and
stop to end point collection; escape to abort without
returning any values).
It is a wrapper for the
grid.locator that behaves more like
locator, the equivalent function intended
for use with
getXY selections are not automatically
marked. Adding common plot parameters to the function
call overrides this behaviour, e.g. to add red symbols
ans <- getXY(col = "red", pch = 4, type = "b")
getXY also provides a mechanism to handle data plotted on
locally scaled axes. See Note below.
getLatLon is wrapper for
getXY for use
GoogleMap outputs and other similarly
georeferenced plots. See Note below.
screenLatticePlot is a crude plot screening function. It is
currently in development.
getXY returns the x and y coordinates of
the selected points on a plot as a list containing two
getLatLon returns the latitude and longitude
values of the selected points on a map as a list
containing two components,
getXY recovers the (x, y) coordinates of points selected
on a previously generated plot.
Some plots, use local scaling. For example, when plotting latitude, longitude data on a map a scale correction may be used to account for the curvature of the Earth. Similarly, if different data series are plotted on primary and secondary axes in a single plot, some or all data may be normalised. In such cases scaling may be local, i.e. what you actually plot may not be exactly what the annotation says it is.
getXY on such plots would recover the actual (x, y)
coordinates of the points selected.
However, corrections can be applied using
if it is supplied, to convert these to the same scale as the axes
annotation. The correction should be a function that can be
applied directly to a standard
getXY output (a list of
y values) and rescale x and y to give
their 'corrected' values.
getLatLon provides an example of the mechanism, and is
for use with georeferenced plots that have been locally scaled
RgoogleMaps functions like
y values and then
to convert the outputs of this step to a list format like that
This function makes extensive use of code developed by others.
lattice: Sarkar, Deepayan (2008) Lattice: Multivariate Data Visualization with R. Springer, New York. ISBN 978-0-387-75968-5
RgoogleMaps: Markus Loecher and Sense Networks (2011). RgoogleMaps: Overlays on Google map tiles in R. R package version 22.214.171.124. http://CRAN.R-project.org/package=RgoogleMaps