From 20959162d975121b5283c4875d761e179a955c2e Mon Sep 17 00:00:00 2001
From: Francesco Nattino <f.nattino@esciencecenter.nl>
Date: Tue, 9 Sep 2025 21:22:08 +0200
Subject: [PATCH 1/3] add test with fully occluded rays

this is failing for now
---
 tests/testthat/test-isovist.R | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/tests/testthat/test-isovist.R b/tests/testthat/test-isovist.R
index 7270c2f..ed53ab5 100644
--- a/tests/testthat/test-isovist.R
+++ b/tests/testthat/test-isovist.R
@@ -186,3 +186,14 @@ test_that("merge_isovists returns the merged polygon, with or without holes", {
   expected <- sf::st_union(isovists)
   expect_equal(actual, expected)
 })
+
+test_that("visor works with fully occluded rays", {
+  viewpoints <- sf::st_sfc(sf::st_point(c(0, 0)), sf::st_point(c(2, 0)))
+  occluders <- sf::st_sfc(
+    create_occluder(1, 0, 2, 1),
+    create_occluder(3, 1, 1, 1)
+  )
+  expect_no_error(
+    get_isovist(viewpoints, occluders = occluders, ray_length = 1)
+  )
+})

From 4496f9dad8d9a8ee7345828378c454b20dc6a47f Mon Sep 17 00:00:00 2001
From: Francesco Nattino <f.nattino@esciencecenter.nl>
Date: Wed, 10 Sep 2025 09:32:20 +0200
Subject: [PATCH 2/3] fix issue with fully occluded rays

---
 R/isovist.R | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/R/isovist.R b/R/isovist.R
index 336b6fb..df31816 100644
--- a/R/isovist.R
+++ b/R/isovist.R
@@ -159,10 +159,16 @@ occlude_rays <- function(rays, occluders = NULL) {
   # Filter the only features intersecting each others
   rays_intersect <- ray_geoms[ray_intersects_occluders]
   occluders_intersect <- occluder_geoms[occluder_intersects_rays]
+  occluders_intersect <- sf::st_union(occluders_intersect)
+
+  # Determine which rays are fully within the occluders and will thus be dropped
+  rays_within_occluders <- sf::st_within(rays_intersect,
+                                         occluders_intersect,
+                                         sparse = FALSE)
 
   # Determine the ray segments that do not overlap with the occluders. For each
-  # ray the segments form (multi)-linestrings
-  diffs <- sf::st_difference(rays_intersect, sf::st_union(occluders_intersect))
+  # ray the segments form (multi)-linestrings. Fully-occluded rays are dropped
+  diffs <- sf::st_difference(rays_intersect, occluders_intersect)
 
   # By casting `diffs` to linestrings, we keep only the first segment of each
   # ray, which, by construction, runs from the original viewpoint to the first
@@ -170,8 +176,12 @@ occlude_rays <- function(rays, occluders = NULL) {
   rays_occluded <- sf::st_cast(diffs, "LINESTRING", group_or_split = FALSE) |>
     suppressWarnings()
 
+  # Determine the indices of the partially-occluded rays, i.e. the ones that
+  # intersect the occluders and are not fully within the occluders
+  idx <- which(ray_intersects_occluders)[!rays_within_occluders]
+
   # Update the occluded ray geometries and return the sf(c) object
-  ray_geoms[ray_intersects_occluders] <- rays_occluded
+  ray_geoms[idx] <- rays_occluded
   sf::st_set_geometry(rays, ray_geoms)
 }
 

From 3ac03928ef66c52deefef5c92fd8a1592bede2aa Mon Sep 17 00:00:00 2001
From: Francesco Nattino <f.nattino@esciencecenter.nl>
Date: Wed, 10 Sep 2025 09:34:33 +0200
Subject: [PATCH 3/3] update changelog

---
 NEWS.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index 4efdfd3..13ba062 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -9,6 +9,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Added Zenodo and CRAN badges #15
 
+## Fixed
+
+- Isovist can now be computed also if some rays are fully occluded #17
+
 # Version 0.1.0 - 2025-04-03
 
 ## Added