Add st_startpoint

.Rbuildignore

@@ -4,3 +4,5 @@ appveyor.yml
 codecov.yml
 ^docs$
 tic.R
+^.*\.Rproj$
+^\.Rproj\.user$

DESCRIPTION

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

NAMESPACE

@@ -46,6 +46,7 @@ export(st_perimeter)
 export(st_perimeter_2d)
 export(st_snap_to_grid)
 export(st_split)
+export(st_startpoint)
 export(st_subdivide)
 export(st_transform_proj)
 import(sf)

R/RcppExports.R

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

R/startpoint.R

@@ -0,0 +1,17 @@
+#' Return the start and end points from lines
+#' 
+#' @param x line of class \code{sf}, \code{sfc} or \code{sfg}
+#' @export
+#' @details see \url{https://postgis.net/docs/ST_StartPoint.html} and \url{https://postgis.net/docs/ST_EndPoint.html}.
+#' @return \code{sf} object representing start and end points
+#' @examples
+#' library(sf)
+#' m = matrix(c(0, 1, 2, 0, 1, 4), ncol = 2)
+#' l = st_sfc(st_linestring(m))
+#' lwgeom::st_startpoint(l)
+#' l2 = st_sfc(st_linestring(m), st_linestring(m[3:1, ]))
+#' lwgeom::st_startpoint(l2)
+st_startpoint = function(x) {
+  m <- CPL_startpoint(st_geometry(x))
+  st_sfc(lapply(seq_len(nrow(m)), function(i) st_point(m[i,])), crs = st_crs(x))
+}

src/RcppExports.cpp

@@ -246,6 +246,17 @@ BEGIN_RCPP
     return rcpp_result_gen;
 END_RCPP
 }
+// CPL_startpoint
+Rcpp::NumericMatrix CPL_startpoint(Rcpp::List sfc);
+RcppExport SEXP _lwgeom_CPL_startpoint(SEXP sfcSEXP) {
+BEGIN_RCPP
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
+    Rcpp::traits::input_parameter< Rcpp::List >::type sfc(sfcSEXP);
+    rcpp_result_gen = Rcpp::wrap(CPL_startpoint(sfc));
+    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 +304,7 @@ 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_startpoint", (DL_FUNC) &_lwgeom_CPL_startpoint, 1},
     {"_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 +244,21 @@ Rcpp::List CPL_force_polygon_cw(Rcpp::List sfc) {
   }
   return sfc_from_lwgeom(lwgeom_cw);
 }
+
+// [[Rcpp::export]]
+Rcpp::NumericMatrix CPL_startpoint(Rcpp::List sfc) {
+
+  std::vector<LWGEOM *> lwgeom_cw = lwgeom_from_sfc(sfc);
+  Rcpp::NumericMatrix m(lwgeom_cw.size(), 2);
+
+  POINT4D p;
+  for (size_t i = 0; i < lwgeom_cw.size(); i++) {
+    lwgeom_startpoint(lwgeom_cw[i], &p);
+    m(i, 0) = p.x;
+    m(i, 1) = p.y;
+  }
+
+  return m;
+  // next step: get it into sf form
+  // return sfc_from_lwgeom(lwgeom_cw);
+}