On Dec 2, 2013, at 8:02 PM, Mercutio Florid wrote:
> I want to map out a mostly flat area of land, 300 meters on a side.
>
>
> I want to make (x,y,z) triples where x and y vary between -150 and 150 and
> there is just one z value.
>
>
> Eventually I will try to use graphics to actually draw this, but my first
> problem is that I need to get 90601 values by interpolating just 13 actual
> measurements. The measurements are currently unsorted, which might cause
> errors with some functions, and they are in a matrix that looks like this:
> X Y Value
> 1 20 135 105
> 2 -127 69 106
> 3 -98 47 107
> 4 -39 69 105
> 5 49 47 105
> 6 108 69 107
> 7 -9 3 106
> 8 -39 3 106
> 9 -127 -63 105
> 10 -39 -41 108
> 11 -39 -107 106
> 12 79 -63 107
> 13 20 -129 107
I have no idea what sort of "interpolation would make sense here. There is an
'akima' package that does interpretation at irregularly located x-y
coordinates, but after doing a planar fit with scatter3d (which also lets you
look at the points in 3d, I think your points have a rather irregular
cliff-like structure.
rd.txt <- function (txt, header = TRUE, ...)
{
rd <- read.table(textConnection(txt), header = header, ...)
closeAllConnections()
rd
}
dat <- rd.txt(" X Y Value
1 20 135 105
2 -127 69 106
3 -98 47 107
4 -39 69 105
5 49 47 105
6 108 69 107
7 -9 3 106
8 -39 3 106
9 -127 -63 105
10 -39 -41 108
11 -39 -107 106
12 79 -63 107
13 20 -129 107")
library(car)
# will also need rgl
scatter3d(dat$X, dat$Y, dat$Value)
library(akima)
akima.li <- interp(dat$X, dat$Y, dat$Value,
xo=seq(min(dat$X), max(dat$X), length = 100),
yo=seq(min(dat$Y), max(dat$Y), length = 100))
persp(akima.li$z)
persp(akima.li$z, theta=30)
persp(akima.li$z, theta=45)
persp(akima.li$z, theta=60)
--
David.
>
>
> The syntax for the output seems pretty easy:
> x_coord<-seq(from=-150,to=150)
> y_coord<-seq(from=-150,to=150)
> planebreadth=301
> spaceArray<-array(0,c(planebreadth, planebreadth,1))
>
> But what I need to do is somehow interpolate 90601 values into spaceArray,
> based on just 13 measurements.
>
> I looked through some introductory R tutorials such as
>
> cran.r-project.org/doc/manuals/R-intro.html
>
> and I didn't see any examples that seemed to cover this kind of problem.
>
>
>
> I did some web searches and there seem to be many, many ways to do
> interpolation. There are packages like mgcv and DiceKriging. There are
> various packages that mention splines in their descriptions, such as cobs.
>
> What is the easiest way to interpolate this kind of data? Thanks.
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius
Alameda, CA, USA
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