Recovering information from existing lattice plots.
getXY(n = -1, ..., unit = "native", scale.correction = NULL)getLatLon(...,
scale.correction = function(x) {
temp <- MercatorXY2LatLon(x$x, x$y)
as.list(as.data.frame(temp))
})
getXY returns the x and y coordinates of
the selected points on a plot as a list containing two
components, x and y.
getLatLon returns the latitude and longitude
values of the selected points on a map as a list
containing two components, lat and lon.
If positive, the maximum number of points to locate. If negative (default), unlimited.
The unit to use when reporting located points, by
default "native".
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:
trellis.focus for panel selection (if working with multi-panel
plots) and lpoints to set point properties (if marking selected
points). For getLatLon, additional arguments are also passed to
XY2LatLon for x, y to latitude, longitude rescaling.
Karl Ropkins
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 function
grid.locator that behaves more like
locator, the equivalent function intended
for use with plot outputs.
By default getXY selections are not automatically
marked. Adding common plot parameters to the function
call overrides this behaviour, e.g. to add red symbols
and lines.
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
with loaMapPlot and other similarly
georeferenced plots. See Note below.
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 1.1.9.6. http://CRAN.R-project.org/package=RgoogleMaps
In other packages: See grid.locator;
trellis.focus and lpoints in lattice.