Question

我想处理两个光栅图像（Ra和Rb），其中Ra是像素值本身，Rb是其邻居的值。以sum为例，假设有一个3 * 3的邻居，对于Ra中的每个像素，我将其值加到Rb中相邻像素的值，最后我会得到另一个图像。

R栅格包提供焦点功能，仅适用于一个图像输入，我尝试修改C ++代码（enter link description here）以接受使用Rcpp的两个图像输入。如果Rb的输入图像中没有缺失值，则修改后的代码可以很好地工作。但是，如果Rb中有NA，则R始终中止。具体而言，在第二次或第三次测试中止。它可能类似于this post。但是，如果输入Rb中没有NA，它就不会崩溃。好像我没有正确处理NA。我对C ++没有深入了解，有人可以帮我查一下吗？

这是我的cpp文件：

#include <Rcpp.h>
#include <R.h>
#include <Rinternals.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <Rmath.h>
#include "Rdefines.h"
#include "R_ext/Rdynload.h"

using namespace Rcpp;
// [[Rcpp::export]]
NumericVector focal_quantile(NumericVector xd, int ngbb, NumericVector sf) {
  //the imges are transfered to vector, ngbb is the size of the window  
  R_len_t i, j, k, q;
  int wrows = ngbb;
  int wcols = ngbb;
  int wn = wrows * wcols;

  int nrow = 6;//the input raste has 6 rows
  int ncol = 7;//the input raste has 7 cols

  int n = nrow * ncol;
  NumericVector xans(n);
  NumericVector xx(wn);

  int wr = floor(wrows / 2);
  int wc = floor(wcols / 2);

  int nwc = ncol - wc - 1;
  int col = 0;

  // first rows
  for (i = 0; i < ncol*wr; i++) {// the first row, the resutl is set as NA as the neighbor does not have nine values   
    xans[i] = R_NaReal; 
  }

  for (i = ncol*wr; i < (ncol * (nrow-wr)); i++) {//start from the second row
    col = i % ncol;
    if ((col < wc) | (col > nwc)) {//the first pixel of the second is also set as NA
      xans[i] = R_NaReal;
    } else {// to get the nine values in the 3*3 windows
      q = 0;
      for (j = -wr; j <= wr; j++) {
        for (k = -wc; k <= wc; k++) {
          xx[q] = xd[j * ncol + k + i]; 
          q++;
        }
      }
      xx = na_omit(xx);
      int n_qt = xx.size();
      if (n_qt > 0){//
        xans[i]=sum(xx)+100*sf[i];// here is the calculation, my goal is more complicated than this example
      } else {
        xans[i] = R_NaReal;//R_NaReal
      }

    }
  }
  // last rows
  for (i = ncol * (nrow-wr); i < n; i++) {  
    xans[i] = R_NaReal;
  }
  return(xans);
}

然后使用sourceCpp

编译它

生成示例数据以进行测试

  rr=raster(nrow=6,ncol=7)## example for Ra
  projection(rr)="+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84"
  rr[]=(2:43)*10
  rrqt=rr/43 ## example for Rb
  ##it works fine, if there is no NA in Ra
  #rr[1:10]=NA #window of global enviornment is refleshing and then aborts with such NAs 
  focal_quantile(rr[],3,rrqt[])

示例结果

 [1]       NA       NA       NA       NA       NA       NA       NA       NA 118918.6 130810.5 142702.3 154594.2 166486.0       NA       NA
[16] 202161.6 214053.5 225945.3 237837.2 249729.1       NA       NA 285404.7 297296.5 309188.4 321080.2 332972.1       NA       NA 368647.7
[31] 380539.5 392431.4 404323.3 416215.1       NA       NA       NA       NA       NA       NA       NA       NA

结果NA是可以接受的，因为窗口中没有九个值。对于这样的例子，我改变了光栅rr的值（没有NA）。它工作顺利。当我在rr中引入NA时，例如上面代码的第六行。全局环境窗口令人耳目一新，Rstudio中止。

会话信息

R version 3.3.0 (2016-05-03)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] Rcpp_0.12.11 raster_2.5-8 sp_1.2-3    

loaded via a namespace (and not attached):
[1] rgdal_1.2-5     tools_3.3.0     grid_3.3.0      lattice_0.20-35

非常感谢！

Answer 1

首先，您应该只使用#include <Rcpp.h>语句。您要添加的其他标题不需要或已包含在Rcpp.h中。

其次，在Rcpp中引用NA s的NumericVector值的正确方法是使用NA_REAL 不 R的R_NaReal。

第三，你有一个越界错误。如果将括号从[]切换到()，则检测到边界。 Rcpp 0.12.11的错误是：

“索引越界：[index = 3; extent = 3]。”

因此，这会创建一个触发RStudio崩溃的"Undefined Behavior" (UB)。

有问题的一行是：

xx(q) = xd(j * ncol + k + i); 
^^^^^

现在，您可能会说这没有意义，因为xx的长度永远不应该是3.但是，这一行有问题的原因是因为您正在更改{{1}中的值当您使用以下内容删除xx值时

NA

如果这是目标，你应该真正声明一个新的xx = na_omit(xx);向量，或者更新常量以确保避免越界错误。

实施

xy

测试用例：

#include <Rcpp.h>

// [[Rcpp::export]]
Rcpp::NumericVector focal_quantile(Rcpp::NumericVector xd,
                                   int ngbb,
                                   Rcpp::NumericVector sf) {
  //the imges are transfered to vector, ngbb is the size of the window  
  R_len_t i, j, k, q;
  int wrows = ngbb;
  int wcols = ngbb;
  int wn = wrows * wcols;

  int nrow = 6;//the input raste has 6 rows
  int ncol = 7;//the input raste has 7 cols

  int n = nrow * ncol;
  Rcpp::NumericVector xans(n);
  Rcpp::NumericVector xx(wn);

  int wr = floor(wrows / 2);
  int wc = floor(wcols / 2);

  int nwc = ncol - wc - 1;
  int col = 0;

  // first rows
  for (i = 0; i < ncol*wr; i++) {// the first row, the resutl is set as NA as the neighbor does not have nine values   
    xans[i] = NA_REAL; 
  }

  for (i = ncol*wr; i < (ncol * (nrow-wr)); i++) {//start from the second row
    col = i % ncol;
    if ((col < wc) | (col > nwc)) {//the first pixel of the second is also set as NA
      xans[i] = NA_REAL;
    } else {// to get the nine values in the 3*3 windows
      q = 0;
      for (j = -wr; j <= wr; j++) {
        for (k = -wc; k <= wc; k++) {
          xx[q] = xd[j * ncol + k + i]; 
          q++;
        }
      }
      Rcpp::NumericVector xx_subset = na_omit(xx);
      int n_qt = xx_subset.size();
      if (n_qt > 0){//
        xans[i]=sum(xx_subset)+100*sf[i];// here is the calculation, my goal is more complicated than this example
      } else {
        xans[i] = NA_REAL;//NA_REAL
      }

    }
  }

  // last rows
  for (i = ncol * (nrow-wr); i < n; i++) {  
    xans[i] = NA_REAL;
  }
  return(xans);
}

输出：

library("raster")
rr = raster(nrow=6,ncol=7)## example for Ra
projection(rr) = "+proj=lcc +lat_1=48 +lat_2=33 +lon_0=-100 +ellps=WGS84"
rr[] = (2:43)*10
rrqt = rr/43 ## example for Rb
rr[1:10] = NA 
focal_quantile(rr[],3,rrqt[])

旁注

如果您查看要翻译的代码，请注意有naonly部分后跟na组件。所以，翻译不一定是1-1。

R使用带有NA输入的Rcpp崩溃/中止

1 个答案:

实施