library(sgeostat)
library(akima)


     data(akima)
     # linear interpolation
     akima.li <- interp(akima$x, akima$y, akima$z)
     image(akima.li$x,akima.li$y,akima.li$z)
     contour(akima.li$x,akima.li$y,akima.li$z,add=T)
     points(akima$x,akima$y)
 
     # increase smoothness
     akima.smooth <- interp(akima$x, akima$y, akima$z,
           xo=seq(0,25, length=100),  yo=seq(0,20, length=100))
     image(akima.smooth$x,akima.smooth$y,akima.smooth$z)
     contour(akima.smooth$x,akima.smooth$y,akima.smooth$z,add=T)
     points(akima$x,akima$y)
     # use triangulation library to
     # show underlying triangulation:
     library(tripack)
     plot(tri.mesh(akima),add=T,lty="dashed")
 
     # use only 15 points (interpolation only within convex hull!)
     akima.part <- interp(akima$x[1:15],akima$y[1:15],akima$z[1:15])
     image(akima.part$x,akima.part$y,akima.part$z)
     contour(akima.part$x,akima.part$y,akima.part$z,add=T)
     points(akima$x[1:15],akima$y[1:15])
 
     # spline interpolation, use 5 points to calculate derivatives
     akima.spl <- interp.old(akima$x, akima$y, akima$z,
           xo=seq(0,25, length=100),  yo=seq(0,20, length=100),ncp=5)
     image(akima.spl$x,akima.spl$y,akima.spl$z)
     contour(akima.spl$x,akima.spl$y,akima.spl$z,add=T)
     points(akima$x,akima$y)
 
     # example with duplicate points
     data(airquality)
     air <- airquality[(!is.na(airquality$Temp) &
                        !is.na(airquality$Ozone) &
                        !is.na(airquality$Solar.R)),]
     # gives an error:
     # air.ip <- interp(air$Temp,air$Solar.R,air$Ozone)
     # use mean of duplicate points:
     air.ip <- interp(air$Temp,air$Solar.R,air$Ozone,duplicate="mean")