R help - Jun 2003 - Isocontour-lines of spatial data on a rectangular grid (not plots!)

Dear R-Listers,

I have spatial data on an equidistant rectangular grid, similar to
topographic data. I know that there are quite a few R-packages or base
functions that provide nice iso-contours plot, but I don't want a plot, just
the smoothed isocontour line of ONE level (e.g. 10 mm).

Data sets are large, so it would be preferable if the availability of
regular grid data could be exploited, and the fact that I only need ONE
isocontour line.  Polynomial fits are not adequate, but loess works nicely
for the plots. Akima/interp might be a little too general, and if I remember
Brian Ripley's comments correctly, the coefficients are "only for
internal
use".

Can someone suggest me a package?


Dieter Menne

On Mon, 16 Jun 2003, Dieter Menne wrote:
> Dear R-Listers,
> 
> I have spatial data on an equidistant rectangular grid, similar to
> topographic data. I know that there are quite a few R-packages or base
> functions that provide nice iso-contours plot, but I don't want a plot,
just
> the smoothed isocontour line of ONE level (e.g. 10 mm).
> 
> Data sets are large, so it would be preferable if the availability of
> regular grid data could be exploited, and the fact that I only need ONE
> isocontour line.  Polynomial fits are not adequate, but loess works nicely
> for the plots. Akima/interp might be a little too general, and if I
remember
> Brian Ripley's comments correctly, the coefficients are "only for
internal
> use".
> 
> Can someone suggest me a package?
> 
A similar question:

https://www.stat.math.ethz.ch/pipermail/r-help/2003-May/032907.html

was asked by Renaud Lancelot in late May. The source package for clines is 
at:

http://www.stat.auckland.ac.nz/~paul/R/clines_1.0.tar.gz

which returns chosen contours from an input matrix as used in contour().

Roger
> 
> Dieter Menne
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 
-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no

Hi Dieter,

The "sm" (smoothing methods library) of Bowman and Azzalini (Bowman,
AW
& Azzalini A (1997) Applied Smoothing Techniques for Data Analysis: The 
Kernel Approach with S-Plus Illustrations, Clarendon Press, Oxford).

Check out pages 9 and 10 (Figure 1.8).

I don't know how large is large for you as a data set, so I can't say 
how well it goes. I would say it goes as well as anything else.

Rohan Sadler

Dieter Menne wrote:
>Dear R-Listers,
>
>I have spatial data on an equidistant rectangular grid, similar to
>topographic data. I know that there are quite a few R-packages or base
>functions that provide nice iso-contours plot, but I don't want a plot,
just
>the smoothed isocontour line of ONE level (e.g. 10 mm).
>
>Data sets are large, so it would be preferable if the availability of
>regular grid data could be exploited, and the fact that I only need ONE
>isocontour line.  Polynomial fits are not adequate, but loess works nicely
>for the plots. Akima/interp might be a little too general, and if I remember
>Brian Ripley's comments correctly, the coefficients are "only for
internal
>use".
>
>Can someone suggest me a package?
>
>
>Dieter Menne
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>
-- 
PhD Student, Ecosystems Research Group (ERGO)
School of Plant Biology (Botany), Faculty of Natural & Agricultural
Sciences,
The University of Western Australia, 35 Stirling Highway, Crawley  WA  6009,
Australia

Ph:  +61 8 9380 7914
Fax: +61 8 9380 7925
email: rsadler at agric.uwa.edu.au
ERGO's web site:<http://www.botany.uwa.edu.au/ergo>