0

I have .nc file sizing around 651 MB with a couple of datasets (daily) (rr_mrg_19810101_20181231_ENACT.nc) data. I need to convert (rr_mrg_19810101_20181231_ENACT.nc) dataset to multiple GeoTIFF (one .tif for each time slice, monthly). Similarly, i want to read the time series. But I found

Error in .local(x, time, ...) : 
time must has the same length as the number of layers in RasterBrick][1]

Here is what i did

library(raster)
library(zoo)
library(rts)
       
TRF = brick("rr_mrg_19810101_20181231_ENACT.nc")
crs(TRF) <- "+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 
+towgs84=0,0,0"
Awash_Extent<-c(37,44, 7,12)
Awash_E_resize<- crop(TRF,Awash_Extent)

Awash_Month<-seq(as.Date('1981-01-01'),as.Date('2018-12-31'),by = 
"month")

rt <- rts(Awash_E_resize, Awash_Month) 

write.rts(Awash_E_resize, filename='Awash_TRF_1981_2018_mon.tif', 
overwrite=TRUE)

Can you help me on the issue?

Robert Hijmans
  • 40,301
  • 4
  • 55
  • 63
Addisu D
  • 17
  • 5

1 Answers1

1

Something as simple as this can do that

library(raster)
b <- brick("rr_mrg_19810101_20181231_ENACT.nc")
writeRaster(b, "timeslice.tif", bylayer=TRUE)

Based on your expanded question:

Read the values with terra (no need for other packages)

library(terra)    
TRF = rast("rr_mrg_19810101_20181231_ENACT.nc")
Awash_Extent<-c(37,44, 7,12)
Awash_E_resize<- crop(TRF,Awash_Extent)

I create something similar here:

A <- rast(ext(37,44, 7,12), nlyr=365)
values(A) <- runif(size(A))
terra::time(A) <- seq(as.Date('1981-01-01'), as.Date('1981-12-31'), 1)

Now aggregate by month:

m <- months(time(A))
f <- factor(m, levels=unique(m))

B <- tapp(A, m, fun=sum)
B
#class       : SpatRaster 
#dimensions  : 10, 10, 12  (nrow, ncol, nlyr)
#resolution  : 0.7, 0.5  (x, y)
#extent      : 37, 44, 7, 12  (xmin, xmax, ymin, ymax)
#coord. ref. : lon/lat WGS 84 
#source      : memory 
#names       :  January, February,    March,    April,      May,     June, ... 
#min values  : 12.49764, 10.47718, 11.80974, 11.29624, 11.01105, 10.83298, ... 
#max values  : 18.90536, 16.95743, 20.57114, 18.12099, 18.46543, 18.98500, ...

You could add a filename= argument to tapp, but if you want to save the layers as separate files you can use writeRaster instead. But with terra you need to provide the filenames yourself.

 fnames <- paste0("rain_", 1:nlyr(B), ".tif")
 writeRaster(B, fnames, overwrite=T)

(there is a warning about file_ext that you can ignore)

Robert Hijmans
  • 40,301
  • 4
  • 55
  • 63
  • Dear Robert Hijmans, Thank you for your help! To clarify it again rr_mrg_19810101_20181231_ENACT.nc is daily rainfall data. My intention is just to aggregate the daily information to month and export it as .tif for each monthly slice. – Addisu D Apr 23 '22 at 06:15
  • Please edit your question to say that, and can you show what you have tried? – Robert Hijmans Apr 23 '22 at 06:24
  • library(raster) b <- brick("rr_mrg_19810101_20181231_ENACT.nc") writeRaster(b, "timeslice.tif", bylayer=TRUE) Thank you This works nicely for daily basis. I need it for Monthly analysis. Thank you! – Addisu D Apr 23 '22 at 06:35
  • Dear Robert, Thank you again for your time and response. I followed the code to my dataset and found a change in spatial resolution of the area. What is wrong with that? – Addisu D Apr 23 '22 at 09:01