如何使用栅格列表创建栅格马赛克? [英] How can I create raster mosaic using list of rasters?

问题描述

我需要创建几个光栅马赛克.我在 64 位 Windows 计算机上使用 Package raster version 2.0-31.我相信我做了功课，检查了所有可能的博客并向一些同事提出了这个问题，但仍然找不到解决方案.

I need to create several raster mosaics. I'm using Package raster version 2.0-31 on a 64bits windows computer. I believe I did my homework checking through all possible blogs and asking this question to some colleagues, but still can't find a solution.

我遇到的问题是，如果我的网格列在光栅对象中，我将无法创建马赛克.我发现 这个例子，我虽然我可以申请，但我得到一个奇怪的错误信息.下面的例子代表了我的问题:

The problem I have is that I can't create a mosaic if my grids are listed in a raster object. I found this example that I though I could apply, but not, I get a weird error message. The example below represents my problem:

r <- raster()
r1 <- crop(r, extent(-10, 10, -10, 10))
r2 <- crop(r, extent(0, 20, 0, 20))
r3 <- crop(r, extent(10, 30, 10, 30))

r1[] <- 1:ncell(r1)
r2[] <- 1:ncell(r2)
r3[] <- 1:ncell(r3)
rasters1 <- list(r1, r2, r3)

mos <- mosaic(rasters1,fun=mean)

这是我得到的错误:

Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function ‘mosaic’ for signature ‘"list", "missing"’

我还尝试了此处，但也没有用.

I also tried the function suggested in here, but didn't work either.

fmerge <- function(rasters1, fun, ...){
  ex <- raster(union(rasters1))
  res(ex) <- res(rasters1[[1]])
  for( i in 1:length(rasters1) )
    rasters[[i]] <- merge(rasters1[[i]], ex)
  rasters <- stack(rasters1)
  fun(rasters1, ...)
}

rfm <- fmerge(rasters1, mean, na.rm=T)

这是错误信息:

Error in raster(union(rasters1)) : 
  error in evaluating the argument 'x' in selecting a method for function 'raster': Error in as.vector(y) : argument "y" is missing, with no default

推荐答案

这似乎是较新版本的光栅的回归.您的示例代码在 raster 1.9-70(和 R 2.13.1)中按预期运行，但给出的错误与您在 raster 2.0-41(ad R 2.15.3)中收到的错误相同.您可能希望通过电子邮件向维护者 Robert J. Hijmans 指出这一点.

This seems to be a regression in newer versions of raster. Your example code runs as expected in raster 1.9-70 (and R 2.13.1) but gives the same error as you receive in raster 2.0-41 (ad R 2.15.3). You may wish to email the maintainer Robert J. Hijmans to point this out.

与此同时，这个问题是可以解决的.查看光栅 1.9-70 中的马赛克 和 mosaic in raster 2.0-41，可以看到接受列表的方法被移除了.相反，现在只有一种方法可以接受单个栅格.所以如果你有很多栅格，你应该像这样调用函数:

In the meantime, this problem can be worked around. Looking at the difference in code between mosaic in raster 1.9-70 and mosaic in raster 2.0-41, you can see that the method that accepted a list has been removed. Instead, there is now only a method that accepts individual rasters. So if you have lots of rasters, you are meant to call the function like this:

mos1 <- mosaic(r1, r2, r3, fun=mean)

这不是很方便，但是，如果您正在构建要动态镶嵌的栅格列表.R 确实有一个辅助函数可以在这种情况下为您提供帮助，do.call.do.call 所做的是接受一个函数和一个列表，并使用列表中的项目作为参数调用该函数.所以你可以使用它，只要你将 fun=mean 添加到你的参数列表中:

This isn't very convenient, however, if you are building your list of rasters to mosaic dynamically. R does have a helper function to help you in this kind of situation, do.call. What do.call does is take a function and a list, and it calls that function using the items in the list as arguments. So you can use this, as long as you add fun=mean to your argument list:

rasters1.mosaicargs <- rasters1
rasters1.mosaicargs$fun <- mean
mos2 <- do.call(mosaic, rasters1.mosaicargs)

您可以仔细检查这两种方法是否给出相同的结果:

You can double check that these two methods give the same results:

stopifnot(identical(mos1, mos2))

这可以包装成一个简单的便利函数，并绑定到相关的调用签名，因此您的原始代码无需修改即可运行:

This can be wrapped into a simple convenience function that and bound to the relevant call signature, so your original code will work unmodified:

setMethod('mosaic', signature(x='list', y='missing'), 
function(x, y, fun, tolerance=0.05, filename=""){
    stopifnot(missing(y))
    args <- x
    if (!missing(fun)) args$fun <- fun
    if (!missing(tolerance)) args$tolerance<- tolerance
    if (!missing(filename)) args$filename<- filename
    do.call(mosaic, args)
})

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