Merge pull request #975 from jmarshallnz/fix_st_difference

Fix st_difference on a single sfc so it works on entirely contained geometries correctly.

src/geos.cpp

@@ -956,8 +956,8 @@ Rcpp::List CPL_nary_difference(Rcpp::List sfc) {
 					contained = chk_(GEOSContains_r(hGEOSCtxt, out[tree_sel[j]].get(), geom.get()));
 					if (contained)
 						break;
-					// test if the items overlap with geom
-					if (chk_(GEOSOverlaps_r(hGEOSCtxt, geom.get(), out[tree_sel[j]].get()))) {
+					// test if the items intersect with geom
+					if (chk_(GEOSIntersects_r(hGEOSCtxt, geom.get(), out[tree_sel[j]].get()))) {
 						// if they do then erase overlapping parts from geom
 						geom = geos_ptr(GEOSDifference_r(hGEOSCtxt, geom.get(), out[tree_sel[j]].get()), hGEOSCtxt);
 						if (geom == nullptr)

tests/testthat/test_geos.R

@@ -240,6 +240,12 @@ test_that("st_difference works with fully contained geometries", {
 	#expect_equal(out1[[2]][[1]], correct_geom[[2]][[1]])
 	#expect_equal(out2[[1]][[1]], correct_geom[[1]][[1]])
 	#expect_equal(out2[[2]][[1]], correct_geom[[2]][[1]])
+	# check change in order
+	in3 = st_sfc(list(pl2, pl1))
+	correct_geom = list(pl2, st_difference(pl1, pl2))
+	out3 = st_difference(in3)
+	expect_equal(correct_geom[[1]], out3[[1]])
+	expect_equal(correct_geom[[2]], out3[[2]])
 })
 
 test_that("binary operations work on sf objects with common column names", {