Fix regression in OBJ loader

Regression happened in #6047 If a OBJ file only defines vertices and vertex normals (same number), but no faces, then vertices and vertex normals should be associated one-to-one in the order they appear. This worked before, but since the mentioned pull request, normals would be zero in this case.
PointCloudLibrary · Feb 4, 2025 · 460d9fc · 460d9fc
1 parent 6e4eb4e
commit 460d9fc
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Showing 2 changed files with 52 additions and 2 deletions.
diff --git a/io/src/obj_io.cpp b/io/src/obj_io.cpp
@@ -550,6 +550,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PCLPointCloud2 &cloud,
 
   //vector[idx of vertex]<accumulated normals{x, y, z}>
   std::vector<Eigen::Vector3f> normal_mapping;
+  bool normal_mapping_used = false;
 
   // std::size_t rgba_field = 0;
   for (std::size_t i = 0; i < cloud.fields.size (); ++i)
@@ -662,6 +663,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PCLPointCloud2 &cloud,
             n = (n < 0) ? normal_idx + n : n - 1;
 
             normal_mapping[v] += normals[n];
+            normal_mapping_used = true;
           }
         }
         continue;
@@ -675,7 +677,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PCLPointCloud2 &cloud,
     return (-1);
   }
 
-  if (!normal_mapping.empty())
+  if (normal_mapping_used && !normal_mapping.empty())
   {
     for (uindex_t i = 0, main_offset = 0; i < cloud.width; ++i, main_offset += cloud.point_step)
     {
@@ -685,6 +687,16 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PCLPointCloud2 &cloud,
         memcpy(&cloud.data[main_offset + cloud.fields[f].offset], &normal_mapping[i][j], sizeof(float));
     }
   }
+  else if (cloud.width == normals.size())
+  {
+    // if obj file contains vertex normals (same number as vertices), but does not define faces,
+    // then associate vertices and vertex normals one-to-one
+    for (uindex_t i = 0, main_offset = 0; i < cloud.width; ++i, main_offset += cloud.point_step)
+    {
+      for (int j = 0, f = normal_x_field; j < 3; ++j, ++f)
+        memcpy(&cloud.data[main_offset + cloud.fields[f].offset], &normals[i][j], sizeof(float));
+    }
+  }
 
   double total_time = tt.toc ();
   PCL_DEBUG ("[pcl::OBJReader::read] Loaded %s as a dense cloud in %g ms with %d points. Available dimensions: %s.\n",
@@ -983,6 +995,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PolygonMesh &mesh,
 
   //vector[idx of vertex]<accumulated normals{x, y, z}>
   std::vector<Eigen::Vector3f> normal_mapping;
+  bool normal_mapping_used = false;
 
   // std::size_t rgba_field = 0;
   for (std::size_t i = 0; i < mesh.cloud.fields.size (); ++i)
@@ -1093,6 +1106,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PolygonMesh &mesh,
             n = (n < 0) ? vn_idx + n : n - 1;
 
             normal_mapping[v] += normals[n];
+            normal_mapping_used = true;
           }
         }
         mesh.polygons.push_back (face_vertices);
@@ -1107,7 +1121,7 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PolygonMesh &mesh,
     return (-1);
   }
 
-  if (!normal_mapping.empty())
+  if (normal_mapping_used && !normal_mapping.empty())
   {
     for (uindex_t i = 0, main_offset = 0; i < mesh.cloud.width; ++i, main_offset += mesh.cloud.point_step)
     {
@@ -1117,6 +1131,16 @@ pcl::OBJReader::read (const std::string &file_name, pcl::PolygonMesh &mesh,
         memcpy(&mesh.cloud.data[main_offset + mesh.cloud.fields[f].offset], &normal_mapping[i][j], sizeof(float));
     }
   }
+  else if (mesh.cloud.width == normals.size())
+  {
+    // if obj file contains vertex normals (same number as vertices), but does not define faces,
+    // then associate vertices and vertex normals one-to-one
+    for (uindex_t i = 0, main_offset = 0; i < mesh.cloud.width; ++i, main_offset += mesh.cloud.point_step)
+    {
+      for (int j = 0, f = normal_x_field; j < 3; ++j, ++f)
+        memcpy(&mesh.cloud.data[main_offset + mesh.cloud.fields[f].offset], &normals[i][j], sizeof(float));
+    }
+  }
 
   double total_time = tt.toc ();
   PCL_DEBUG ("[pcl::OBJReader::read] Loaded %s as a PolygonMesh in %g ms with %zu points and %zu polygons.\n",

diff --git a/test/io/test_io.cpp b/test/io/test_io.cpp
@@ -1144,6 +1144,32 @@ TEST(PCL, OBJRead)
   remove ("test_obj.mtl");
 }
 
+TEST(PCL, loadOBJWithoutFaces)
+{
+  std::ofstream fs;
+  fs.open ("test_obj.obj");
+  fs << "v -1.000000 -1.000000 1.000000\n"
+        "v -1.000000 1.000000 1.000000\n"
+        "v 1.000000 -1.000000 1.000000\n"
+        "v 1.000000 1.000000 1.000000\n"
+        "vn -1.0000 0.0000 0.0000\n"
+        "vn 0.0000 0.0000 -1.0000\n"
+        "vn 1.0000 0.0000 0.0000\n"
+        "vn 0.0000 1.0000 0.0000\n";
+
+  fs.close ();
+  pcl::PointCloud<pcl::PointNormal> point_cloud;
+  pcl::io::loadOBJFile("test_obj.obj", point_cloud);
+  EXPECT_EQ(point_cloud.size(), 4);
+  EXPECT_NEAR(point_cloud[0].normal_x, -1.0, 1e-5);
+  EXPECT_NEAR(point_cloud[1].normal_z, -1.0, 1e-5);
+  EXPECT_NEAR(point_cloud[2].normal_x, 1.0, 1e-5);
+  EXPECT_NEAR(point_cloud[3].normal_y, 1.0, 1e-5);
+  EXPECT_NEAR(point_cloud[1].normal_y, 0.0, 1e-5);
+  EXPECT_NEAR(point_cloud[3].normal_z, 0.0, 1e-5);
+  remove ("test_obj.obj");
+}
+
 //////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
 struct PointXYZFPFH33