R help - Mar 2009 - Plot contour inside a polygon

Dear,

I am trying to plot contours (with filled.contour function) inside UK area, so
that no contours are plotted over the sea. I was wondering if anyone can help me
with this task and if I can get any suggestions how to do that.


Thank you,

Irina

Irina Foss
Environmental Research Institute
North Highland College
UHI Millennium Institute
Castle Street
Thurso, Caithness
Scotland
KW14 7JD
United Kingdom

Tel:  +44 (0) 1847 889 587
Fax: +44 (0) 1847 890 014
http://www.eri.ac.uk/sub/staff.php?id=11

On 3/20/2009 8:40 AM, Irina Foss wrote:
> Dear,
> 
> I am trying to plot contours (with filled.contour function) inside UK area,
so that no contours are plotted over the sea. I was wondering if anyone can help
me with this task and if I can get any suggestions how to do that.

If you have a grid of values over a larger area than the UK, set the 
values outside the UK to NA, then contour won't draw contours there.

For example, to get contours only in the circle x^2 + y^2 < 1:

x <- seq(-1, 1, len=100)
y <- seq(-1, 1, len=100)
z <- outer(x, y, function(x,y) ifelse(x^2 + y^2 < 1, sin(x)+cos(y), NA))
contour(x,y,z)

theta <- seq(0, 2*pi, len=256)
lines(cos(theta), sin(theta))

The maps package contains map.where() to say what region a particular 
grid point is in; just check that it's a UK region.

Duncan Murdoch