[R-sig-Geo] Combine two polygons

[Roger Bivand]

On Fri, 28 Apr 2023, Michael Sumner wrote:

> fwiw, a method with geodata/terra
>
> cyp <- geodata::gadm(country = c("CYP", "XNC"), path = tempdir(), version =
> "3.6")
>
> terra::aggregate(cyp)
>

and as per 
https://github.com/r-spatial/evolution/blob/main/pkgapi_230305_refs.csv.

> see ?terra::writeVector to write it out
>
> (rgdal is very old and you should abandon it, it will be removed from
> support by the end of this year)

Thank you! Yes, sp will by default switch to using sf in place of rgdal 
for creating "CRS" objects, and under sp::spTransform in June, and all 
three retiring packages rgdal, rgeos, and maptools will be gone by October 
2023. An sp release will appear in May with a transition guide.

It seems that terra does not have an object corresponding to sp's "CRS" or 
sf's "crs". As far as I can see, one needs to create an empty 
SpatVector/SpatRaster object and assign a CRS, coerce to "Spatial", and 
extract its slot. If this makes sense, sp could use terra (and 
raster, needed for coercion) rather than sf where workflows did not 
otherwise use sf. Very grateful for input here or 
https://github.com/r-spatial/evolution/issues.

Roger

>
>
> (just as an aside, we can't hit the geodata vector urls directly with gdal
> as we can with the rasters, as they are in an R specific format)
>
> Cheers, Mike
>
>
> On Fri, Apr 28, 2023 at 10:52 AM Ben Tupper <btupper using bigelow.org> wrote:
>
>> Hi,
>>
>> You might try st_union() from the sf package
>> https://r-spatial.github.io/sf/articles/sf3.html#geometrical-operations
>>
>>
>>
>> On Thu, Apr 27, 2023 at 5:37 PM Miluji Sb <milujisb using gmail.com> wrote:
>>
>>> Dear all,
>>>
>>> I am using the country-level shapefile from GADM. I would like to merge
>>> Cyprus and North Cyprus into one polygon. Is this possible? I am using
>>> rgdal to read the shapefile, subset, and then rewrite it. Any help will
>> be
>>> highly appreciated.
>>>
>>> ##
>>> world <- readOGR("~/gadm36_levels_shp", layer = "gadm36_0")
>>>
>>> Best regards,
>>>
>>> Milu
>>>
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>>>
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>>
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>>
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>
>
>

-- 
Roger Bivand
Emeritus Professor
Department of Economics, Norwegian School of Economics,
Postboks 3490 Ytre Sandviken, 5045 Bergen, Norway.
e-mail: Roger.Bivand using nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en