[R-sig-Geo] Not perfect match between the bounding box for a EPSG when projected (st_bbox from sf)

[Manuel Spínola]

Thank you very much Roger.

Manuel

El vie, 26 mar 2021 a las 8:47, Roger Bivand (<Roger.Bivand using nhh.no>)
escribió:

> On Thu, 25 Mar 2021, Manuel Spínola wrote:
>
> > Dear list members,
> >
> > I am working with the epsg 5367.
> >
> > The information for this epsg according to this website (
> > https://epsg.io/5367) is:
> >
> > WGS84 bounds:
> > -90.45 2.15
> > -81.43 11.77
> >
> > Projected bounds:
> > -218963.01 239235.14
> > 780173.56 1302793.77
> >
> > When I create a box with st_bbox from the package sf and transform the
> > object I don't get the same bounding box that I was expecting.  Is it a
> > fair expectation?
>
> No. Firstly, epsg.io is not an EPSG service. Secondly, two different
> definitions are offered. I think that this works (sf 0.9-8):
>
> pts1 <- st_sfc(list(st_point(c(-90.45, 2.15)), st_point(c(-81.43,
>   11.77))), crs="OGC:CRS84")
> st_transform(pts1, "EPSG:5367")
> # POINT (-218962 239233.5)
> # POINT (780173.7 1302793)
> o <- sf_proj_pipelines("OGC:CRS84", "EPSG:5367")
> o$definition
> st_transform(pts1, "EPSG:5367", pipeline = o$definition[1])
> # POINT (-218962 239233.5)
> # POINT (780173.7 1302793)
> # Costa Rica - onshore and offshore, accuracy 1.0 m, code 8969 [grid]
> st_transform(pts1, "EPSG:5367", pipeline = o$definition[2])
> # POINT (-218963 239235.1)
> # POINT (780173.6 1302794)
> # Costa Rica - onshore and offshore, accuracy 1.0 m, code 5376 (default)
> # [grid]
>
> So, as in https://github.com/r-spatial/sf/issues/1634, treating epsg.io
> as
> authoritative (especially when there are different transformation
> pipelines in play) may be unhelpful.sf/PROJ chooses a different pipeline
> as default than epsg.io.
>
> This roundtrips:
>
> st_transform(st_transform(pts1, "EPSG:5367"), "OGC:CRS84")
> # POINT (-90.45 2.15)
> # POINT (-81.43 11.77)
> # Costa Rica - onshore and offshore, accuracy 1.0 m, code 8969 [grid]
>
> but for epsg.io's default, one needs to intervene manually to choose
> pipelines both ways that are not sf's default choices.
>
> Of course, here I am not using the bounding box polygon, because its
> projected version is not a rectangle, so its bounding box expands the
> range, especially further from the equator.
>
> Hope this clarifies,
>
> Roger
>
> >
> > b <- st_bbox(c(xmin = -90.45, xmax = -81.43, ymax = 11.77, ymin = 2.15),
> > crs = st_crs(4326))
> >
> > b <- st_as_sfc(b)
> >
> > b_5367 <- st_transform(b, crs = 5367)
> >
> > b_5367
> >
> > Geometry set for 1 feature
> > Geometry type: POLYGON
> > Dimension:     XY
> > Bounding box:  xmin: -218962 ymin: 237951.9 xmax: 785959.7 ymax: 1309622
> > Projected CRS: CR05 / CRTM05POLYGON ((-218962 239233.5, 785959.7
> 237951.9, ...
> >
> >
> >
> >
>
> --
> Roger Bivand
> 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



-- 
*Manuel Spínola, Ph.D.*
Instituto Internacional en Conservación y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspinola using una.cr <mspinola using una.ac.cr>
mspinola10 using gmail.com
Teléfono: (506) 8706 - 4662
Personal website: Lobito de río <https://sites.google.com/site/lobitoderio/>
Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/>

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