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
작은 영역을 자르려고하면 잘 동작합니다.때때로 작물이 범주 형 래스터에 NAs를 도입하는 이유는 무엇입니까?
ext <- extent(-68,-64,-2,2)
r1 <- crop(r,ext) # works fine
이 오류로 인해 writeRaster로 파일을 저장할 수 없지만 무슨 일이 일어나고 있는지 알 수 없습니다.
다른 사용자가 related question에서이 문제를 발견했습니다. 원래 래스터의 일부분이 잘리는 지에 따라 RAT (Raster Attribute Table)가 손상됩니다. 왜 이런 일이 일어나는 지 아직 모르겠다.
> 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
'sum (is.na (r1 []))'은 0을 반환합니다 ... 시각적으로 첫 번째 '자르기'의 결과를 확인 했습니까? – loki
@loki 네, 0을 반환합니다. 그리고'r1 [is.na (r1)]'은 NULL을 반환합니다. 첫 번째 작물이 정상적으로 그려집니다. – Rodrigo
경고는 아무 의미없이 발생합니까? – loki