如何对栅格 NA 值使用多种提取方法

Question

I'm quite new to r and coding and I'd appreciate any help please.

I have two data sets: A raster object with degree heating weeks (a remotely sensed measure of cumulative sea surface temperature). A set of coordinates recording where coral bleaching occurred.

I have successfully extracted the DHW values at each coordinate using the following: raster::extract(mydata, coords, method="simple")

However, there are many NA values. I believe that this is because many coordinates are close to the coast and occupy predominantly land-filled pixels.

I would like to use methods="bilinear" to interpolate values for the NA cells and methods="simple" for the non-NA cells. I would like the output to be one object.

I wrote the following function:

  if(is.na(dhw_raster[])){
    raster::extract(dhw_raster, coords, method="bilinear")
  } else {
    raster::extract(dhw_raster, coords, method="simple")
  }
}````




However, it returns only the method="simple" values, and this warning:

In if (is.na(dhw_raster[])) { :
  the condition has length > 1 and only the first element will be used

Any advice would be great :)

Answer 1

You can probably do something like this

x <- raster::extract(mydata, coords, method="simple")
y <- raster::extract(mydata, coords, method="bilinear")

And now replace the missing values in x with the values in y (and then use x )

i <- is.na(x)
x[i] <- y[i]