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

[boB Rudis]

rgdal 1-1.4 (built from rforge) has "showP4" (and "showWKT"):

  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]]'

  showP4(prj_1)
  ## [1] "+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000
+y_0=-100000 +datum=OSGB36 +units=m +no_defs "

On Tue, Jan 5, 2016 at 6:20 AM, boB Rudis <bob at rudis.net> wrote:
> It's too early I guess as it didn't occur to me that if writing it out
> locally was naff using an external service is more so. The
> SpatialReference "importFromESRI()" function doesn't seem to be mapped
> in rgdal. That would be the function needed to avoid a
> write-out/external call.
>
> On Tue, Jan 5, 2016 at 5:57 AM, boB Rudis <bob at rudis.net> wrote:
>> 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
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at r-project.org
>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo