On 10/24/2010 02:55 PM, David Winsemius wrote:
On Oct 24, 2010, at 4:30 AM, Lorenzo Isella wrote:
Dear All,
I would like to plot a scalar (e.g. a temperature) on a
non-rectangular domain (or even better: I would simply like to be able
to draw a contour plot on an arbitrary 2D domain). I wonder if there
is any tool to achieve that with R. I did some online search in
particular on the list archives, found several queries similar to this
one but was not able to find any conclusive answer.
One implemented approach to this exists with the rms/Hmisc package
combination. The perimeter function is used to define a region within
which the are a sufficient number of cases and the perimeter object is
passed to the bplot function, which is a wrapper for a lattice
contourplot call. There is no reason you couldn't emulate
I am interested in the following 2 options
(1) just read a file of the form
x1 y1 z1
x2 y2 x2
... ... ...
xn yn zn
where the set of {xi} and {yi} are coordinates on an arbitrary domain
and {zi} are the values of the scalar for the corresponding {x,y}
coordinates.
(2) Sometimes the domain where I want to draw a contour plot is
nothing too fancy and the scalar itself is given by an analytical
function. Consider e.g. the case of a circle of radius R=pi/2 centered
about the origin and a function like
z=f(x,y)=abs(cos(y))
That defines the contours but does not restrict the domain.
NB: in this case a satisfactory solution could be to plot z on a
rectangular grid and then clip a circular region
To fix the ideas, the final result in this case (with a colorjet map)
should look like this
http://dl.dropbox.com/u/5685598/scalar_plot.pdf
And that color encoded output would not be the output of a contourplot
but is more like a levelplot or an image plot. Nonetheless, the
perimeter and bplot combination can deliver a similar result if you
supply either code or data as a suitable test case for analysis and
display.
I agree that contour plot was a misleading name for what I had in mind.
I'll try your suggestion and the one by Uwe about rgl and post again if
I had troubles. As to the domain of the function, at least in case (1),
that should arise from the collected data points in (x,y) if the
sampling is dense enough.
Cheers
Lorenzo
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