对栅格执行空间操作时，terra 会将 INT1U 范围之外的值替换为 NA

Question

我正在使用来自 landfire.gov 的生物物理设置栅格数据集。当我最初使用 terra::rast() 读取数据集时，一切似乎都在工作。但是，当我尝试使用多边形裁剪数据时，0-255 范围之外的所有值都将替换为 NA。如果我尝试将此栅格投影到新的坐标参考系统，超出此范围的值也会被删除。谁能解释为什么这个栅格被限制为数据类型 INT1U 的值以及我如何绕过它？

下面我提供了一个可重现的代码示例，说明我如何尝试处理此数据集。此示例依赖于两个公共数据集：

1. Biophysical Settings from Landfire.gov
2. North Carolina state boundary from nconemap.gov（将其下载为 shapefile）

   library(terra)
   library(dplyr)
   library(sf)
   
   # Establish paths to required files.  
   # ** These will need to be replaced with your local paths
   bpsDirPath <- "./dataRaw/envTerr/LF2020_BPS_220_CONUS/"
   ncBoundaryPath <- "C:/Users/Eliot-KDV/Desktop/NCDOT_State_Boundary/NCDOT_State_Boundary.shp"
   
   
   # Read in biophysicall setting raster data
   bpsRaw <- terra::rast(paste0(bpsDirPath, "Tif/LC20_BPS_220.tif"))
   # Read in codebook for bps categories
   codeBook <- read.csv(paste0(bpsDirPath, "CSV_Data/LF20_BPS_220.csv"))
   # Read in North Carolina state boundary
   ncBoundary <- read_sf(ncBoundaryPath)
   
   # Set levels of biophysical setting to category names provided in codebook instead 
   #   of category codes.  This step is unnecessary but makes plot more readable 
   levels(bpsRaw) <- dplyr::select(codeBook, VALUE, BPS_NAME)
   
   # Take a look before any spatial operations, note that North Carolina countains
   #   numerous different levels
   plot(bpsRaw)
   
   # Transform ncBoundary to epsg:5070 so bps and ncBoundary share the same CRS
   ncBoundary <- st_transform(ncBoundary, "epsg:5070")
   
   # Crop bps to north carolina boundary
   bpsNc <- terra::crop(bpsRaw, vect(ncBoundary), mask = TRUE)
   
   # Look after cropping to NC boundary, now it only contains Open Water and 
   #   Barren-Rock/Sand/Clay
   plot(bpsNc)
   
   

   将生物物理设置栅格裁剪到北卡罗来纳州边界后，会显示警告“检测到的值超出数据类型 INT1U 的限制”。

   我尝试使用 terraOptions() 将默认数据类型设置为 INT2S 但无济于事。如果有人能解释为什么会发生这种情况以及我如何纠正它，那就太好了！

   更新：

   现有植被高度代码：

   # This does not work as expected
   library(terra)
   
   evhRaw <- terra::rast("./dataRaw/envTerr/LF2022_EVH_220_CONUS/Tif/LC22_EVH_220.tif")
   nc <- terra::vect("./dataTidy/cadastral/NCDOT_State_Boundary/NCDOT_State_Boundary.shp")
   ncp <- project(nc, evhRaw)
   evhNc <- terra::crop(evhRaw, ncp, mask = TRUE)
   
   # This is where the issue occurs
   evhNcPlane <- terra::project(evhNc, "epsg:2264")
   

   生物物理设置代码：

   # This code works as expected
   library(terra)
   
   bpsRaw <- terra::rast("./dataRaw/envTerr/LF2020_BPS_220_CONUS/Tif/LC20_BPS_220.tif")
   nc <- terra::vect("./dataTidy/cadastral/NCDOT_State_Boundary/NCDOT_State_Boundary.shp")
   ncp <- project(nc, bpsRaw)
   bpsNc <- terra::crop(bpsRaw, ncp, mask = TRUE)
   
   bpsNcPlane <- terra::project(bpsNc, "epsg:2264")
   
   

Answer 1

您使用的是当前版本的“terra”吗？我问是因为这对我很有效：

library(terra)
bpsRaw <- terra::rast("./LF2020_BPS_220_CONUS/Tif/LC20_BPS_220.tif"))
## this is how you change the category of interest
activeCat(bpsRaw) <- "BPS_NAME"

ncp <- project(nc, bpsRaw)
bpsNc <- terra::crop(bpsRaw, ncp, mask = TRUE)