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
Isocontour-lines of spatial data on a rectangular grid (not plots!)
3 messages · Dieter Menne, Roger Bivand, rohan sadler
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
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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
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