[R-sig-Geo] WKT coordinate system string (PRJ) to PROJ.4

[boB Rudis]

This may not be optimal as it uses an external service:

  prj_to_epsg <- function(prj) {

    require(sp)
    require(httr)
    require(jsonlite)

    res <- GET("http://prj2epsg.org/search.json",
               query=list(exact=TRUE,
                          error=TRUE,
                          mode="wkt",
                          terms=prj))

    # one shld prbly do more error checking than this
    stop_for_status(res)

    dat <- fromJSON(content(res, as="text", flatten=TRUE))

    # NOTE: there could be more in dat$codes if prj was ambiguous
    CRS(paste0("+init=epsg:", dat$codes[1, "code"]))

  }

  prj <- paste0(readLines("110m_admin_1_states_provinces_shp.prj"))
  prj_to_epsg(prj)
  ## CRS arguments:
  ##  +init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84
  ## +towgs84=0,0,0

  prj_1 <- 'PROJCS["Transverse_Mercator",
    GEOGCS["GCS_OSGB 1936",
    DATUM["D_OSGB_1936",
    SPHEROID["Airy_1830",6377563.396,299.3249646]],
    PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",49],
    PARAMETER["central_meridian",-2],
    PARAMETER["scale_factor",0.9996012717],
    PARAMETER["false_easting",400000],
    PARAMETER["false_northing",-100000],
    UNIT["Meter",1]]'
  prj_to_epsg(prj_1)
  ## CRS arguments:
  ##  +init=epsg:27700 +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717
  ## +x_0=400000 +y_0=-100000 +datum=OSGB36 +units=m +no_defs +ellps=airy
  ## +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894

On Tue, Jan 5, 2016 at 5:09 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> Hello, is there any R-level way to convert a WKT/PRJ *coordinate system*
> string to PROJ.4 used by sp/rgdal?
>
> (Previously I've written out to SHP/PRJ, and read back in with rgdal, but
> that's obviously a bit naff.)
>
> (I know you can rgeos::readWKT and wkb::readWKB for *geometry*).
>
> Cheers, Mike.
>
>
>
>
> --
> Dr. Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> 203 Channel Highway
> Kingston Tasmania 7050 Australia
>
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>
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