prj <- "+proj=stere +lat_0=-90 +lat_ts=-70 +datum=WGS84"
f <- "~/FastIce_70_2006.nc"
ex <- c(-2700000, -2700000 + 5625 * 1000, -2397000, -2397000 + 4700 * 1000)
nc <- ncdf4::nc_open(f)
print(nc) ## tells us metadata like
#> File ~/FastIce_70_2006.nc (NC_FORMAT_NETCDF4):
#>
#> 7 variables (excluding dimension variables):
#> double x[X] (Contiguous storage)
#> long_name: x co-ordinates
#> units: meters
#> description: Meters in polar stereographic projection (true latitude -70) for the centre of each pixel
#> double y[Y] (Contiguous storage)
#> long_name: y co-ordinates
#> units: meters
#> description: Meters in polar stereographic projection (true latitude -70) for the centre of each pixel
#> float latitude[X,Y] (Contiguous storage)
#> long_name: latitude
#> units: degrees_north
#> description: Latitude values for the centre of each pixel
#> float longitude[X,Y] (Contiguous storage)
#> long_name: longitude
#> units: degrees_east
#> description: Longitude values for the centre of each pixel
#> double area[X,Y] (Contiguous storage)
#> long_name: area
#> units: km2
#> description: Per-pixel grid area
#> int date_alt[time] (Contiguous storage)
#> long_name: alternative date format
#> description: Start date of 15 or 20-day image mosaic window in YYYYMMDD format
#> byte Fast_Ice_Time_series[X,Y,time] (Chunking: [938,784,4]) (Compression: level 1)
#> long_name: Fast Ice Time Series
#> description: Classified surface type: 0 = pack ice or ocean; 1 = continent; 2 = islands; 3 = ice shelf; 4 = fast ice; 5 = manual fast ice edge; 6 = auto fast ice edge.
#> FillValue: 0
#>
#> 3 dimensions:
#> time Size:24
#> long_name: time
#> units: days since 2000-1-1 0:0:0
#> description: Start date of 15- or 20-day image mosaic window.
#> calendar: proleptic_gregorian
#> X Size:5625 (no dimvar)
#> Y Size:4700 (no dimvar)
#>
#> 8 global attributes:
#> title: Fast ice time series
#> institution: Institute for Marine and Antarctic Studies, University of Tasmania
#> source: MODIS 15-day composite images and automated edge detection
#> history: Version 2.2
#> references: Fraser et al., 2020 (Earth System Science Data, submitted)
#> comment: This is the lat_ts=-70 version of the data - year 2006
#> contact: Alex Fraser ([email protected])
#> Conventions: CF-1.7
##Classified surface type: 0 = pack ice or ocean; 1 = continent; 2 = islands; 3 = ice shelf; 4 = fast ice; 5 = manual fast ice edge; 6 = auto fast ice edge.
time <- as.Date("2000-01-01") + ncdf4::ncvar_get(nc, "time")
ncdf4::nc_close(nc)
library(terra)
#> terra 1.8.10
r <- rast(f, "Fast_Ice_Time_series")
#> [1] "vobjtovarid4: **** WARNING **** I was asked to get a varid for dimension named X BUT this dimension HAS NO DIMVAR! Code will probably fail at this point"
#> [1] "vobjtovarid4: **** WARNING **** I was asked to get a varid for dimension named Y BUT this dimension HAS NO DIMVAR! Code will probably fail at this point"
set.ext(r, ext(ex))
set.crs(r, crs(prj))
points <- cbind(
lon = c(136.5, 140.2, 143.8), # Example longitudes
lat = c(-65.5, -65.3, -66.8) # Example latitudes
)
prjpoints <- project(points, to = prj, from = "EPSG:4326")
extract(r, prjpoints)
#> Fast_Ice_Time_series_1 Fast_Ice_Time_series_2 Fast_Ice_Time_series_3
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_4 Fast_Ice_Time_series_5 Fast_Ice_Time_series_6
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_7 Fast_Ice_Time_series_8 Fast_Ice_Time_series_9
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_10 Fast_Ice_Time_series_11 Fast_Ice_Time_series_12
#> 1 4 4 0
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_13 Fast_Ice_Time_series_14 Fast_Ice_Time_series_15
#> 1 4 4 4
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_16 Fast_Ice_Time_series_17 Fast_Ice_Time_series_18
#> 1 4 4 4
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_19 Fast_Ice_Time_series_20 Fast_Ice_Time_series_21
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0
#> Fast_Ice_Time_series_22 Fast_Ice_Time_series_23 Fast_Ice_Time_series_24
#> 1 0 0 0
#> 2 0 0 0
#> 3 0 0 0Created on 2025-01-20 with reprex v2.1.1