add WKT conversion

* adds `st_astext` and `st_asewkb`
* enables `lwgeom_to_wkt` through `CPL_sfc_to_wkt`

DESCRIPTION

@@ -40,4 +40,5 @@ Collate:
 	perimeter.R
 	clockwise.R
 	geod.R
+	wkt.R
 RoxygenNote: 6.0.1

NAMESPACE

@@ -29,6 +29,8 @@ S3method(st_transform_proj,sf)
 S3method(st_transform_proj,sfc)
 S3method(st_transform_proj,sfg)
 export(lwgeom_extSoftVersion)
+export(st_asewkt)
+export(st_astext)
 export(st_force_polygon_cw)
 export(st_geod_area)
 export(st_geod_azimuth)

R/RcppExports.R

@@ -81,6 +81,10 @@ CPL_force_polygon_cw <- function(sfc) {
     .Call('_lwgeom_CPL_force_polygon_cw', PACKAGE = 'lwgeom', sfc)
 }
 
+CPL_sfc_to_wkt <- function(sfc, precision) {
+    .Call('_lwgeom_CPL_sfc_to_wkt', PACKAGE = 'lwgeom', sfc, precision)
+}
+
 CPL_proj_version <- function(b = FALSE) {
     .Call('_lwgeom_CPL_proj_version', PACKAGE = 'lwgeom', b)
 }

R/wkt.R

@@ -0,0 +1,31 @@
+#' Return Well-known Text representation of simple feature geometry
+#'
+#' Return Well-known Text representation of simple feature geometry or coordinate reference system
+#' @param x object of class `sfg`, `sfc` or `crs``
+#' @param precision number of digits to print
+#' @param EWKT Use Postgis Enhanced WKT (includes srid)
+#' @name st_astext
+#' @details The returned WKT representation of simple feature geometry conforms to the
+#' [simple features access](http://www.opengeospatial.org/standards/sfa) specification and extensions (if `EWKT = TRUE`),
+#' [known as EWKT](http://postgis.net/docs/using_postgis_dbmanagement.html#EWKB_EWKT), supported by
+#' PostGIS and other simple features implementations for addition of SRID to a WKT string.
+#' @md
+#' @examples 
+#' library(sf)
+#' pt <- st_sfc(st_point(c(1.0002,2.3030303)), crs = 4326)
+#' st_astext(pt, 3, TRUE)
+#' @export
+st_astext <- function(x, precision = 12, EWKT = FALSE) {
+  if (!EWKT) st_crs(x) <- NA_crs_
+  CPL_sfc_to_wkt(x, precision = precision)
+}
+
+#' @name st_astext
+#' @inheritParams st_astext
+#' @details `st_asewkt()` returns the Well-Known Text (WKT) representation of 
+#' the geometry with SRID meta data.
+#' @md
+#' @export
+st_asewkt <- function(x, precision) {
+  st_astext(x, precision, EWKT = TRUE)
+}

lwgeom.Rproj

@@ -17,3 +17,4 @@ AutoAppendNewline: Yes
 BuildType: Package
 PackageUseDevtools: Yes
 PackageInstallArgs: --no-multiarch --with-keep.source
+PackageRoxygenize: rd,collate,namespace

src/RcppExports.cpp

@@ -246,6 +246,18 @@ BEGIN_RCPP
     return rcpp_result_gen;
 END_RCPP
 }
+// CPL_sfc_to_wkt
+Rcpp::CharacterVector CPL_sfc_to_wkt(const Rcpp::List sfc, const int precision);
+RcppExport SEXP _lwgeom_CPL_sfc_to_wkt(SEXP sfcSEXP, SEXP precisionSEXP) {
+BEGIN_RCPP
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
+    Rcpp::traits::input_parameter< const Rcpp::List >::type sfc(sfcSEXP);
+    Rcpp::traits::input_parameter< const int >::type precision(precisionSEXP);
+    rcpp_result_gen = Rcpp::wrap(CPL_sfc_to_wkt(sfc, precision));
+    return rcpp_result_gen;
+END_RCPP
+}
 // CPL_proj_version
 std::string CPL_proj_version(bool b);
 RcppExport SEXP _lwgeom_CPL_proj_version(SEXP bSEXP) {
@@ -293,6 +305,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_lwgeom_CPL_perimeter", (DL_FUNC) &_lwgeom_CPL_perimeter, 2},
     {"_lwgeom_CPL_is_polygon_cw", (DL_FUNC) &_lwgeom_CPL_is_polygon_cw, 1},
     {"_lwgeom_CPL_force_polygon_cw", (DL_FUNC) &_lwgeom_CPL_force_polygon_cw, 1},
+    {"_lwgeom_CPL_sfc_to_wkt", (DL_FUNC) &_lwgeom_CPL_sfc_to_wkt, 2},
     {"_lwgeom_CPL_proj_version", (DL_FUNC) &_lwgeom_CPL_proj_version, 1},
     {"_lwgeom_CPL_linesubstring", (DL_FUNC) &_lwgeom_CPL_linesubstring, 4},
     {NULL, NULL, 0}

src/lwgeom.cpp

@@ -244,3 +244,15 @@ Rcpp::List CPL_force_polygon_cw(Rcpp::List sfc) {
   }
   return sfc_from_lwgeom(lwgeom_cw);
 }
+
+// [[Rcpp::export]]
+Rcpp::CharacterVector CPL_sfc_to_wkt(const Rcpp::List sfc, const int precision) {
+  std::vector<LWGEOM *> lwgeom_cw = lwgeom_from_sfc(sfc);
+  size_t wkt_size = 0;
+  Rcpp::CharacterVector out;
+  for (size_t i = 0; i < lwgeom_cw.size(); i++) {
+    out.push_back(lwgeom_to_wkt(lwgeom_cw[i], WKT_EXTENDED, precision, &wkt_size));
+  }
+  return out;
+}
+

tests/testthat/test-as_text.R

@@ -0,0 +1,21 @@
+context("test-as_text.R")
+library(sf)
+
+test_that("Prints Points", {
+  pt <- st_sfc(st_point(c(1.0002,2.3030303)), crs = 4326)
+  expect_equal(st_astext(pt, 3), "SRID=4326;POINT(1 2.3)")
+  expect_equal(st_astext(pt, 3, FALSE), "POINT(1 2.3)")
+  expect_equal(st_astext(pt, 4, FALSE), "POINT(1 2.303)")
+  expect_equal(st_astext(pt, 10, FALSE), "POINT(1.0002 2.3030303)")
+})
+
+test_that("Prints Polygons and Lines", {
+  pol <- st_sfc(st_polygon(list(
+    rbind(c(0,0),c(0.5,0),c(0.5,0.5),c(0.5,0),c(1,0),c(1,1),c(0,1),c(0,0))
+    )))
+  txt <- "POLYGON((0 0,0.5 0,0.5 0.5,0.5 0,1 0,1 1,0 1,0 0))"
+  expect_equal(st_astext(pol), txt)
+  ln <- st_cast(pol, "LINESTRING")
+  txt <- "LINESTRING(0 0,0.5 0,0.5 0.5,0.5 0,1 0,1 1,0 1,0 0)"
+  expect_equal(st_astext(ln), txt)
+})