Unexpected behaviour with spatSample(method='stratified', ext=...,)

[barnabasharris]

I'm not sure I understand the behavior of the following. I'm trying to take stratified samples of a categorical raster using spatSample, whilst also using the ext=... argument to limit the area of the raster to sample. However, the sample locations returned are positioned along the top of the raster. If I remove method='stratified' then the expected behaviour occurs.

library(terra)
r <-  rast(xmin=-2,  xmax=-1, ymin=51,  ymax=52,  crs='EPSG:4326',  resolution=0.01,  vals = sample(letters[1:4], 10000, replace=T))
r.grid <- rast(xmin=-2, xmax=-1, ymin=51, ymax=52, crs='EPSG:4326', resolution=0.1)
r.pol <- as.polygons(r.grid)
r.pol$id <- paste0('p',1:nrow(r.pol))

plot(r)
lines(r.grid)

r.samp.strat <- spatSample(r, size=40, method='stratified', replace=T,  ext = ext(r.pol[45,]),  xy=T )
points(r.samp.strat[,1:2], col='red')

r.samp.default <- spatSample(r,  size=40, method='random', replace=T, ext = ext(r.pol[45,]),  xy=T )
points(r.samp.default[,1:2], col='blue')

R version 4.4.0 (2024-04-24)
Platform: x86_64-pc-linux-gnu
Running under: Ubuntu 20.04.6 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/openblas-pthread/libblas.so.3 
LAPACK: /usr/lib/x86_64-linux-gnu/openblas-pthread/liblapack.so.3;  LAPACK version 3.9.0

locale:
 [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C               LC_TIME=en_GB.UTF-8       
 [4] LC_COLLATE=en_GB.UTF-8     LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8   
 [7] LC_PAPER=en_GB.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       

time zone: Europe/London
tzcode source: system (glibc)

attached base packages:
[1] parallel  stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] patchwork_1.2.0        ggplot2_3.5.1          tibble_3.2.1          
 [4] stringr_1.5.1          Microsoft365R_2.4.0    here_1.0.1            
 [7] janitor_2.2.0          broom_1.0.6            qs_0.26.3             
[10] cobalt_4.5.5           marginaleffects_0.23.0 spatialRF_1.1.4       
[13] WeightIt_1.3.1         ENMevalDEV_2.0.4       magrittr_2.0.3        
[16] tidyr_1.3.1            dplyr_1.1.4            purrr_1.0.2           
[19] terra_1.7-78          

loaded via a namespace (and not attached):
  [1] RColorBrewer_1.1-3   rstudioapi_0.16.0    farver_2.1.1         ENMeval_2.0.4       
  [5] fs_1.6.3             vctrs_0.6.5          base64enc_0.1-3      rstatix_0.7.2       
  [9] leafsync_0.1.0       htmltools_0.5.7      virtualspecies_1.6   raster_3.6-26       
 [13] cellranger_1.1.0     pROC_1.18.5          caret_6.0-94         GenSA_1.1.14        
 [17] huxtable_5.5.6       parallelly_1.36.0    KernSmooth_2.23-24   htmlwidgets_1.6.4   
 [21] plyr_1.8.9           stars_0.6-5          lubridate_1.9.3      elbow_0.0.0.9000    
 [25] lifecycle_1.0.4      iterators_1.0.14     pkgconfig_2.0.3      fastmap_1.1.1       
 [29] Matrix_1.6-5         R6_2.5.1             future_1.33.1        snakecase_0.11.1    
 [33] AzureAuth_1.3.3      digest_0.6.34        colorspace_2.1-1     furrr_0.3.1         
 [37] rprojroot_2.0.4      RSpectra_0.16-1      leafem_0.2.3         crosstalk_1.2.1     
 [41] ggpubr_0.6.0         lwgeom_0.2-14        fansi_1.0.6          timechange_0.3.0    
 [45] httr_1.4.7           polyclip_1.10-6      abind_1.4-5          compiler_4.4.0      
 [49] proxy_0.4-27         withr_3.0.0          doParallel_1.0.17    backports_1.5.0     
 [53] carData_3.0-5        viridis_0.6.5        DBI_1.2.3            AzureGraph_1.3.4    
 [57] ggforce_0.4.2        ggsignif_0.6.4       MASS_7.3-60.0.1      lava_1.7.3          
 [61] rappdirs_0.3.3       tmaptools_3.1-1      leaflet_2.2.2        classInt_0.4-10     
 [65] ModelMetrics_1.2.2.2 tools_4.4.0          units_0.8-5          tmap_3.3-4          
 [69] future.apply_1.11.1  nnet_7.3-19          glue_1.7.0           leafgl_0.1.1        
 [73] nlme_3.1-165         grid_4.4.0           sf_1.0-16            reshape2_1.4.4      
 [77] generics_0.1.3       recipes_1.0.9        predicts_0.1-11      gtable_0.3.4        
 [81] class_7.3-22         dismo_1.3-14         data.table_1.15.0    RApiSerialize_0.1.3 
 [85] RcppProgress_0.4.2   sp_2.1-4             xml2_1.3.6           stringfish_0.16.0   
 [89] car_3.1-2            utf8_1.2.4           foreach_1.5.2        pillar_1.9.0        
 [93] ggspatial_1.1.9      splines_4.4.0        tweenr_2.0.3         lattice_0.22-5      
 [97] survival_3.7-0       tidyselect_1.2.0     spatialrisk_0.7.1    knitr_1.45          
[101] gridExtra_2.3        stats4_4.4.0         xfun_0.42            hardhat_1.3.1       
[105] colourvalues_0.3.9   timeDate_4032.109    stringi_1.8.3        codetools_0.2-19    
[109] filematrix_1.3       cli_3.6.2            RcppParallel_5.1.7   rpart_4.1.23        
[113] munsell_0.5.0        dichromat_2.0-0.1    Rcpp_1.0.12          readxl_1.4.3        
[117] globals_0.16.2       png_0.1-8            XML_3.99-0.16.1      ggh4x_0.2.8         
[121] gower_1.0.1          assertthat_0.2.1     geohashTools_0.3.3   listenv_0.9.1       
[125] viridisLite_0.4.2    ipred_0.9-14         scales_1.3.0         prodlim_2023.08.28  
[129] e1071_1.7-14         ggridges_0.5.6       crayon_1.5.2         rlang_1.1.3         
[133] rvest_1.0.4 

[rhijmans]

Thank you for reporting this bug. Fixed.

[barnabasharris]

No worries. Thanks for an awesome package!