[R-sig-Geo] Spatial joins between sf and stars objects

[Julian M. Burgos]

Thanks Edzer, I should have checked if st_extract kept the order of the rows. In this case, a way to do it more generally is:

sf1 <- bind_cols(st_drop_geometry(sf1),
                 st_extract(st1, sf1))



Edzer Pebesma writes:

> st_join does a spatial join, which comes at a cost; since st_extract
> doesn't change the row order of the sf object, you could as well use
>
> st_extract(st1, sf1) %>% mutate(nums = sf1$nums)
>
> On 03/02/2021 17:10, Julian M. Burgos wrote:
>> Dear list,
>>
>> What would be the best way to do a spatial join between a sf object (of POINT geometry) and a star object, so the sf object gets the values of the corresponding pixels in the star object?  I have done using a combination of st_join and st_extract, but it feels a bit clunky.  Is there a better way?
>>
>> Here is what I have done:
>>
>> ## --------------------------------------------------------------
>> ## Load a stars object
>> st1 <- read_stars(system.file("tif/L7_ETMs.tif", package = "stars")) %>%
>>    slice(band, 1)
>>
>> ## Create an sf object
>>
>> set.seed(100)
>> bb <- st_bbox(st1)
>>
>> sf1 <- tibble(lon = runif(n = 10, min = bb[1], max = bb[3]),
>>                lat = runif(n = 10, min = bb[2], max = bb[4]),
>>                nums = 1:10) %>%
>>    st_as_sf(coords = c("lon", "lat"), crs = st_crs(st1))
>>
>> ## Do the spatial join
>>
>> sf1 <- st_extract(st1, sf1) %>%
>>      st_join(sf1)
>> ## --------------------------------------------------------------
>>
>> Thanks,
>>
>> Julian
>>
>> --
>> Julian Mariano Burgos, PhD
>> Hafrannsóknastofnun, rannsókna- og ráðgjafarstofnun hafs og vatna/
>> Marine and Freshwater Research Institute
>> Botnsjávarsviðs / Demersal Division
>>    Fornubúðir 5, IS-220 Hafnarfjörður, Iceland
>> http://www.hafogvatn.is/
>> Sími/Telephone : +354-5752037
>> Netfang/Email: julian.burgos using hafogvatn.is
>>
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--
Julian Mariano Burgos, PhD
Hafrannsóknastofnun, rannsókna- og ráðgjafarstofnun hafs og vatna/
Marine and Freshwater Research Institute
Botnsjávarsviðs / Demersal Division
  Fornubúðir 5, IS-220 Hafnarfjörður, Iceland
www.hafogvatn.is
Sími/Telephone : +354-5752037
Netfang/Email: julian.burgos using hafogvatn.is