问题描述
library(raster)
r <- raster('glc2000_v1_1') # http://forobs.jrc.ec.europa.eu/products/glc2000/products/glc2000_v1_1_Grid.zip
extent(r)
# class : Extent
# xmin : -180.0045
# xmax : 179.9955
# ymin : -56.01339
# ymax : 89.99554
ext <- extent(-69,-63,-3,3)
r1 <- crop(r,ext)
#Warning message:
#In .getRat(x, ratvalues, ratnames, rattypes) : NAs introduced by coercion
如果我尝试裁切较小的区域，效果很好.
If I try to crop a smaller area, it works fine.
ext <- extent(-68,-64,-2,2)
r1 <- crop(r,ext) # works fine
此错误使我无法使用writeRaster保存文件，但是我不知道发生了什么.
This error is preventing me from saving the file with writeRaster, but I have no idea of what's going on.
另一个用户在与相关的问题中找到了问题. RAT(栅格属性表)已损坏，具体取决于原始栅格的哪一部分被裁剪.仍然不知道为什么会这样.
Another user found the problem in a related question. The RAT (Raster Attribute Table) is being corrupted, depending on which part of the original raster is cropped. Still no idea why this happens.
> ext <- extent(-68,-64,-2,2) # The RAT is copied from the original
> r1 <- crop(r,ext)
> levels(r1)
[[1]]
ID COUNT CLASSNAMES
1 1 12875179 Tree Cover, broadleaved, evergreen
2 2 8688097 Tree Cover, broadleaved, deciduous, closed
3 3 4099003 Tree Cover, broadleaved, deciduous, open
4 4 15080165 Tree Cover, needle-leaved, evergreen
5 5 8054159 Tree Cover, needle-leaved, deciduous
6 6 5606446 Tree Cover, mixed leaf type
7 7 579763 Tree Cover, regularly flooded, fresh water
8 8 115705 Tree Cover, regularly flooded, saline water
9 9 4269938 Mosaic: Tree Cover / Other natural vegetation
10 10 587270 Tree Cover, burnt
11 11 3195387 Shrub Cover, closed-open, evergreen
12 12 15605651 Shrub Cover, closed-open, deciduous
13 13 17560702 Herbaceous Cover, closed-open
14 14 23573022 Sparse herbaceous or sparse shrub cover
15 15 3089962 Regularly flooded shrub and/or herbaceous cover
16 16 21692769 Cultivated and managed areas
17 17 4025653 Mosaic: Cropland / Tree Cover / Other natural vegetation
18 18 3921904 Mosaic: Cropland / Shrub and/or grass cover
19 19 24629888 Bare Areas
20 20 471034157 Water Bodies
21 21 10660085 Snow and Ice
22 22 378999 Artificial surfaces and associated areas
23 23 29056 No Data
> ext <- extent(-69,-63,-3,3) # The RAT is corrupted
> r1 <- crop(r,ext)
> levels(r1)
[[1]]
ID COUNT CLASSNAMES
1 1 8688097 Tree Cover, broadleaved, deciduous, open
2 2 4099003 Tree Cover, needle-leaved, evergreen
3 3 15080165 Tree Cover, needle-leaved, deciduous
4 4 8054159 Tree Cover, mixed leaf type
5 5 5606446 Tree Cover, regularly flooded, fresh water
6 6 579763 Tree Cover, regularly flooded, saline water
7 7 115705 Mosaic
8 8 4269938 Tree Cover / Other natural vegetation
9 9 587270 Tree Cover, burnt
10 10 3195387 Shrub Cover, closed-open, evergreen
11 11 15605651 Shrub Cover, closed-open, deciduous
12 12 17560702 Herbaceous Cover, closed-open
13 13 23573022 Sparse herbaceous or sparse shrub cover
14 14 3089962 Regularly flooded shrub and/or herbaceous cover
15 15 21692769 Cultivated and managed areas
16 16 4025653 Mosaic
17 17 3921904 Cropland / Tree Cover / Other natural vegetation
18 18 24629888 Mosaic
19 19 471034157 Cropland / Shrub and/or grass cover
20 20 10660085 Bare Areas
21 21 378999 Water Bodies
22 22 29056 Snow and Ice
23 23 NA Artificial surfaces and associated areas
24 12875179 NA No Data
推荐答案
该错误消息指示栅格属性表发生了某些错误.该问题与标签上的特殊字符有关.
The error message indicated something wrong happening with the Raster Attribute Table. The problem is related with special characters on the labels.
尤其是看来，半列(:)会以某种方式导致裁剪后的栅格中的类名称分裂".因此，两者
In particular, it appears that semicolumns (:) causes somehow a "splitting" of the class names in the cropped raster. Therefore, as soon as both
和
裁剪范围中包含
个像素，由于多个Mosaic标签导致RAT损坏，从而无法正确保存文件.
pixels were included in the cropped extent, the RAT got corrupted due to multiple Mosaic labels, preventing correct saving of the file.
整理"类名，例如:
levels(r)[[1]]$CLASSNAMES <- stringr::str_replace(levels(r)[[1]]$CLASSNAMES , ":", "-")
解决了问题.
这篇关于为什么农作物有时会在分类栅格上引入NA?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！