Question

我正在尝试将HDF4文件（代表每日海冰浓度）限制为R中的栅格对象。但是，HDF文件本身不包含经度/纬度网格或投影信息，因此应从另一个hdf中提取此类信息文件。

数据格式上的here说：

Data Format
Sea ice concentration maps with two different color scales are available as PNG image. The NIC color scale uses the same colors as the National Ice Center, the "visual" color scale uses white and shades of grey.
There is one file per day per region per color scale.
Sea ice concentration data are available as HDF4 files: There is one file per day per region. Each file contains one two-dimensional array of the sea ice concentration in a polar stereographic grid.
The longitude and latitude coordinates of each pixel in a the HDF4 file are saved in extra files, one file per region for each available resolution.
They are found here: https://seaice.uni-bremen.de/data/grid_coordinates/,  sorted by hemisphere and grid resolution (see also the README file https://seaice.uni-bremen.de/data/grid_coordinates/README).
GEOTIFF files use the NIC color scale and were tested to work with QGIS. Ice concentrations are scaled between 0 and 100, land and missing values are set to 120 (older files: SIC: 0-200, land/NaN: 255).

我尝试使用R通过以下代码加载website：

> require(raster)
> CurrTemp <- tempfile()
> download.file(url = "https://seaice.uni-bremen.de/data/amsre/asi_daygrid_swath/s6250/2003/feb/Antarctic/asi-s6250-20030214-v5.hdf", destfile = CurrTemp, mode = "wb", quiet = T)
> Map1 <- readAll(raster(CurrTemp))
> plot(Map1)
> Map1
class       : RasterLayer 
dimensions  : 1328, 1264, 1678592  (nrow, ncol, ncell)
resolution  : 1, 1  (x, y)
extent      : 0, 1264, 0, 1328  (xmin, xmax, ymin, ymax)
coord. ref. : NA 
data source : in memory
names       : file43fc5b4e68de 
values      : 0, 100  (min, max)

将地图作为栅格对象加载到R中，但坐标错误且没有投影。根据{{3}}，应从this map中提取坐标。

请让我知道如何将这些hdf文件转换为具有正确坐标和投影的栅格对象。

谢谢。

Answer 1

我使用了一个geotiff文件，它们也可以用来查找范围和crs。

library(raster)
raster('asi-AMSR2-s6250-20180922-v5.tif')
#class       : RasterLayer 
#dimensions  : 1328, 1264, 1678592  (nrow, ncol, ncell)
#resolution  : 6250, 6250  (x, y)
#extent      : -3950000, 3950000, -3950000, 4350000  (xmin, xmax, ymin, ymax)
#coord. ref. : +proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs 
#data source : asi-AMSR2-s6250-20180922-v5.tif 
#names       : asi.AMSR2.s6250.20180922.v5 
#values      : 0, 255  (min, max)

现在我知道我能做到

library(raster)
CurrTemp <- tempfile()
download.file(url = "https://seaice.uni-bremen.de/data/amsre/asi_daygrid_swath/s6250/2003/feb/Antarctic/asi-s6250-20030214-v5.hdf", destfile = CurrTemp, mode = "wb", quiet = T)
r <- raster(CurrTemp)

extent(r) <- c(-3950000, 3950000, -3950000, 4350000)
crs(r) <- "+proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs "
# writeRaster(r, 'my_asi-s6250-20030214-v5.tif')

“其他hdf”文件具有单元格的经度/纬度值，但这不是您要的，因为数据没有lon / lat坐标参考系统。

将HDF4转换为栅格；经度/纬度网格的数据在另一个HDF文件中可用

1 个答案: