R中的2D线性插值

Question

我想在R中进行双线性插值，但我无法弄清楚如何使用akima interp函数来实现它，因为我得到一个矩阵半填充数字和一半NA 。这是我的问题的一个例子：

x = rep(c(1,2,3,6,9,12)/12,5)
y = seq(2709,3820,length = 30)
z = seq(9.2,16.5,length = 30)

inter_lin = interp(x,y,z,xo = seq(min(x),max(x),length=100),
                   yo = seq(min(y), max(y), length=100), linear=T)

我还尝试使用interp.surface.grid形式fields功能，但z必须是一个矩阵，其中包含我使用的所有x和y的值不能这样做。

修改 这是我实际拥有的y和z向量：

y = c(2931.076,2901.935,2868.635,2804.006,2760.297,2709.114,2983.466,2969.436,2954.808,2928.802,2915.815,2903.867,
      3043.365,3051.140,3057.960,3079.230,3103.015,3127.245,3118.090,3156.223,3194.574,3291.021,3380.687,3472.676,
      3195.631,3260.866,3331.776,3502.477,3658.052,3829.511)

z = c(10.280984,9.733925, 10.176117, 10.644877, 10.950297, 11.737252, 10.442495, 10.170472, 10.590579, 11.153778 ,11.501962,
  12.066833,11.000000, 11.025000, 11.450000, 12.125000, 12.550000, 12.875000, 12.142495, 11.870472, 12.390579, 13.053778,
  13.501962,14.066833,13.005984, 12.458925, 13.051117, 13.694877, 14.150297, 14.937252)

Answer 1

设置linear = FALSE和extrap = TRUE。

x = rep(c(1,2,3,6,9,12)/12,5)
y = seq(2709,3820,length = 30)
z = seq(9.2,16.5,length = 30)

inter_lin = interp(x,y,z,xo = seq(min(x),max(x),length=100),
                   yo = seq(min(y), max(y), length=100), linear=FALSE, extrap = TRUE)

我认为问题是在边界上插值，这会从边缘向内涟漪。通过线性插值允许外推 - 不 - 可以避免这个问题。

修改

如果插值域仅限于 数据的区域，则结果只是极好的。

library(akima)
library(spatialkernel)
library(fields)

# Create grid
grd <- expand.grid(x = seq(min(x),max(x),length=100), y = seq(min(y), max(y), length=100))

# Find points in convex hull
mask <- pinpoly(cbind(x, y)[chull(x, y),], as.matrix(grd))

# Crop grid to convex hull
grd <- grd[mask == 2,]

# Interpolate to points in convex hull
res <- interpp(x, y, z, xo = grd$x, yo = grd$y)

# Plot results
quilt.plot(res$x, res$y, res$z)