From ripley at stats.ox.ac.uk  Mon Oct  3 18:18:48 2005
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Mon, 3 Oct 2005 17:18:48 +0100 (BST)
Subject: [Rd] interpolation using akima (PR#8174)
In-Reply-To: <20051003161316.35D4A1DA5C@slim.kubism.ku.dk>
References: <20051003161316.35D4A1DA5C@slim.kubism.ku.dk>
Message-ID: <Pine.LNX.4.61.0510031716180.17627@gannet.stats>

Please do read the posting guide and FAQ, as we do ask you to do before 
sending a bug report.

1) Your version of R is not current.

2) akima is a contributed package and you are not the maintainer.

We do ask you not to `behave in this manner'.


On Mon, 3 Oct 2005 jonathan_lees at unc.edu wrote:

> Full_Name: Jonathan Lees
> Version: 2.0.1
> OS: linux-gnu
> Submission from: (NULL) (152.2.75.65)
>
>
> there is a problem with calculating the convex hull in 2-D interpolation using
> the codes interp fromt eh akima package:
>
> x =c(0.6505304, -1.1821562, -0.2600792,  0.7913716)
> y = c(1.0424226,  0.1754048, -1.4523334,  0.2349112)
> z =  c(0.000, 3.042, 0.370, 0.122)
>
>
>   EX = seq(from=min(x), to=max(x), length=100)
>    WHY = seq(from=min(y), to=max(y), length=100)
>
> ZZ = interp(x=x, y=y, z=z, xo=EX, yo=WHY, extrap=FALSE)
>
> plot(x,y, type='n')
> image(ZZ, add=TRUE)
> points(x,y)
> text(x,y,labels=z)
>
> BUG:
> Notice the convex hull is wrong.
> It includes only 3 of the 4 points provided.
> If you add another point near by it does some
> really wierd stuff.
> x = c(x,  -0.3950865)
> y = c(y,  -1.449117)
> z = c(z, .37)
>
>
>
> I do not think it should behave in this manner.


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595



[Rd] interpolation using akima (PR#8174)
Prof Brian Ripley