Usage
exCon(M = NULL, x = seq(0, 1, length.out = nrow(M)), y = seq(0, 1,
length.out = ncol(M)), nlevels = 5, levels = pretty(range(M, na.rm =
TRUE), nlevels), browser = NULL, minify = TRUE)
Details
The computation of the contour lines is handled by
contourLines. The result here, however, is transposed so that the
output has the same orientation as the original matrix. This is necessary because
contour tranposes its output: "Notice that
contour interprets the z matrix as a table of
f(x[i], y[j]) values, so that the x axis corresponds to row number
and the y axis to column number, with column 1 at the bottom, i.e. a 90 degree
counter-clockwise rotation of the conventional textual layout."Interpretation
The contour lines are an interpolation of the data
in the matrix. The slices are the actual values in the matrix row or column
connected point-to-point. Thus a maximum in a slice may not correspond to
a peak in the contour plot.Browser Choice
The browser is called by
browseURL, which
in turn uses options("browser"). Exactly how this is handled
is OS dependent.RStudio Viewer
If browser is NULL, you are using RStudio, and a viewer is specified, this will be called. You can stop this by with options(viewer = NULL).Browser Choice (Mac)
On a Mac, the default browser is called
by /bin/sh/open
which in turn looks at which browser you have set in the system settings. You can
override your default with
browser = "/usr/bin/open -a 'Google Chrome'" for example.
Testing shows that on a Mac, Safari and Chrome perform correctly,
but in Firefox the mouse cursor is slightly offset from the guides. While it
doesn't look quite right, it works correctly (the guides determine which
slice is displayed).Browser Choice (Other Systems)
exCon has been tested
on a Windows 7
professional instance running in VirtualBox using Firefox and Chrome, and
runs correctly (Firefox has the same mouse position issue as mentioned above).Browser Choice & Performance
You can check the performance of
your browser at peacekeeper.futuremark.com The most relevant score for
exCon is the rendering category. In limited testing, Chrome does the best.Performance Limits (YMMV)
On a 4-year old MacBook Pro, with 8 Gb
RAM and an Intel Core i7 chip, a
4000 x 4000 matrix with 5 contour levels
requires about 30 seconds for R to create the contours. The web page displayed
by
Chrome 38 appears to be about 85 Mb in size and the guide movements lag the mouse
movements quite a bit, but it is still usable. Sometimes the page won't load.
The files on disk are about 159 Mb. Firefox 32 will load the 4K x 4K
matrix but performance is too sluggish. On the same computer, a
5000 x 5000 matrix with 5 contour levels
causes Chrome to crash. Testing on a newer Mac with 16 Gb RAM shows that
the browser may be the limiting factor rather than the RAM.