[R] smooth contour lines

[Duncan Murdoch]

  On 27/09/2010 11:11 AM, Czerminski, Ryszard wrote:
> Is there an easy way to control smoothness of the contour lines?
>
> In the plot I am working on due to the undersampling the contour
> lines I am getting are jugged, but it is clear "by eye" these should
> be basically straight lines.

Straight lines should come out straight in our current scheme.  I 
suspect your data contains rounding error or other noise, so the actual 
contours aren't straight.

Curves are currently an issue:  the contouring scheme will generate 
polygonal contours.  If the grid you pass is too coarse, you'll see it.  
For example,

 > x <- 1:5
 > y <- 1:5
 > z <- outer(x, y, function(x,y) (x-2)^2 + (y-3)^2)
 > contour(x,y,z)

gives ugly contours.  The solution to this problem is to use a finer grid:

 > x <- seq(1, 5, len=20)
 > y <- seq(1, 5, len=20)
 > z <- outer(x, y, function(x,y) (x-2)^2 + (y-3)^2)
 > contour(x,y,z)

makes them look quite smooth.  So for your problem, I'd fit a nice 
smooth model to your data, then evaluate it on a fine grid, and you'll 
get nice smooth contours.

Duncan Murdoch

> In maps package I found smooth.map function, but maybe there is a more
> generic way
> of accomplishing the same thing.
>
> Ideally there would be an option to control smoothness of the contour
> lines
> in contourplot(), or levelplot(), but I cannot find a way to do it.
>
> Best regards,
>
> Ryszard Czerminski
> AstraZeneca Pharmaceuticals LP
> 35 Gatehouse Drive
> Waltham, MA 02451
> USA
> 781-839-4304
> ryszard.czerminski at astrazeneca.com
>
>
> --------------------------------------------------------------------------
> Confidentiality Notice: This message is private and may ...{{dropped:11}}
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.