在坐标处提取MODIS数据

Question

我试图在特定位置提取MODIS辐射数据，但是我的代码始终返回NA。问题似乎是我没有正确使用图块中的位置信息。

我将很高兴获得解决方案的帮助。

{

    prod <- "MCD18A2"
    lon <- (-93.62)
    lat <- 42.03
    buffer <- 0.3
    dates <- paste0("2011-12-0",1:2)

    library(MODIS)
    library(rgdal)
    library(sp)

    # create a spatial object from the coordinate(s)
    coordinates = SpatialPoints(coords=cbind(lon, lat), proj4string = CRS('+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0'))
    sinus = CRS("+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs")

    # transform the coordinates
    coordinates_sinus = spTransform(coordinates, sinus)

    e <- extent(lon-buffer, lon+buffer, lat-buffer, lat+buffer)
    tileLayer <- getTile(e)

    target.file <- getHdf(product=prod,
                          begin=dates[1],
                          end=dates[length(dates)],
                          tileH=tileLayer@tileH,
                          tileV=tileLayer@tileV, 
                          # extent=tileLayer@extent, 
                          checkIntegrity = FALSE)

    # convert to raster
    sds <- getSds(as.character(target.file$MCD18A2.006[1]))
    hdf_layer = raster(readGDAL(sds$SDS4gdal[1], as.is = TRUE))

    # extract data
    point = extract(hdf_layer, coordinates_sinus)
}