writeValues() inadvertently rounds values

[pat-s]

I'd expect the values written to a SpatRaster not to be rounded.

library(terra)
#> terra version 1.3.22
r <- rast(nrow = 3, ncol = 4)
writeStart(r, filename = tempfile(fileext = ".tif"))
#> $row
#> [1] 1
#> 
#> $nrows
#> [1] 3
#> 
#> $n
#> [1] 1
v <- c(
  66.3484211266179, 67.8992571263675, 65.2368599385505, 60.0851186590024,
  65.1888453571109, 61.7919525966071, 63.1428918602016, 62.2687846669139,
  63.3999659927921, 65.7038877386742, 68.5510667370152, 58.9081320478074
)
writeValues(r, v, 1, 3)
writeStop(r)
#> class       : SpatRaster 
#> dimensions  : 3, 4, 1  (nrow, ncol, nlyr)
#> resolution  : 90, 60  (x, y)
#> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=longlat +datum=WGS84 +no_defs 
#> source      : file12a0919f3184f.tif 
#> name        :    lyr.1 
#> min value   : 58.90813 
#> max value   : 68.55107

all.equal(as.numeric(values(r)), v)
#> [1] "Mean relative difference: 2.71163e-08"

^{Created on 2021-09-04 by the reprex package (v2.0.1)}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value                                      
#>  version  R version 4.1.1 Patched (2021-08-27 r80829)
#>  os       macOS Big Sur 10.16                        
#>  system   x86_64, darwin17.0                         
#>  ui       X11                                        
#>  language (EN)                                       
#>  collate  en_US.UTF-8                                
#>  ctype    en_US.UTF-8                                
#>  tz       Europe/Zurich                              
#>  date     2021-09-04                                 
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version    date       lib source                            
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#> 
#> [1] /Users/pjs/Library/R/x86_64/4.1/library
#> [2] /Library/Frameworks/R.framework/Versions/4.1/Resources/library

[pat-s]

Seems like I just need to set the proper datatype:

library(terra)
#> terra version 1.3.22
r <- rast(nrow = 3, ncol = 4)
writeStart(r, filename = tempfile(fileext = ".tif"), datatype = "FLT8S")
#> $row
#> [1] 1
#> 
#> $nrows
#> [1] 3
#> 
#> $n
#> [1] 1
v <- c(
  66.3484211266179, 67.8992571263675, 65.2368599385505, 60.0851186590024,
  65.1888453571109, 61.7919525966071, 63.1428918602016, 62.2687846669139,
  63.3999659927921, 65.7038877386742, 68.5510667370152, 58.9081320478074
)
writeValues(r, v, 1, 3)
writeStop(r)
#> class       : SpatRaster 
#> dimensions  : 3, 4, 1  (nrow, ncol, nlyr)
#> resolution  : 90, 60  (x, y)
#> extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
#> coord. ref. : +proj=longlat +datum=WGS84 +no_defs 
#> source      : file1d1f2ffcbadf.tif 
#> name        :    lyr.1 
#> min value   : 58.90813 
#> max value   : 68.55107

all.equal(as.numeric(values(r)), v)
#> [1] TRUE

^{Created on 2021-09-06 by the reprex package (v2.0.1)}

[rhijmans]

That is correct. Use FLT8S for higher precision (and a larger file size).