fix issue with vocab loading taking to long with system opencv

CMakeLists.txt

@@ -12,7 +12,7 @@ ExternalProject_Add(dbow2_src
   GIT_REPOSITORY https://github.com/dorian3d/DBoW2.git
   GIT_TAG master
   UPDATE_COMMAND ""
-  #PATCH_COMMAND ""
+  PATCH_COMMAND patch -p1 < ${CMAKE_CURRENT_LIST_DIR}/fix_fs_iter.patch
   CONFIGURE_COMMAND cd ../dbow2_src && cmake -DCMAKE_BUILD_TYPE=Release
                                              -DCMAKE_INSTALL_PREFIX:PATH=${CATKIN_DEVEL_PREFIX}
                                              -DBUILD_Demo=Off .

fix_fs_iter.patch

@@ -0,0 +1,36 @@
+diff --git a/include/DBoW2/TemplatedVocabulary.h b/include/DBoW2/TemplatedVocabulary.h
+index 6d8d621..c95e72e 100644
+--- a/include/DBoW2/TemplatedVocabulary.h
++++ b/include/DBoW2/TemplatedVocabulary.h
+@@ -1473,12 +1473,12 @@ void TemplatedVocabulary<TDescriptor,F>::load(const cv::FileStorage &fs,
+   m_nodes.resize(fn.size() + 1); // +1 to include root
+   m_nodes[0].id = 0;
+
+-  for(unsigned int i = 0; i < fn.size(); ++i)
++  for(auto iter = fn.begin(); iter != fn.end(); ++iter)
+   {
+-    NodeId nid = (int)fn[i]["nodeId"];
+-    NodeId pid = (int)fn[i]["parentId"];
+-    WordValue weight = (WordValue)fn[i]["weight"];
+-    std::string d = (std::string)fn[i]["descriptor"];
++    NodeId nid = (int)(*iter)["nodeId"];
++    NodeId pid = (int)(*iter)["parentId"];
++    WordValue weight = (WordValue)(*iter)["weight"];
++    std::string d = (std::string)(*iter)["descriptor"];
+
+     m_nodes[nid].id = nid;
+     m_nodes[nid].parent = pid;
+@@ -1493,10 +1493,10 @@ void TemplatedVocabulary<TDescriptor,F>::load(const cv::FileStorage &fs,
+
+   m_words.resize(fn.size());
+
+-  for(unsigned int i = 0; i < fn.size(); ++i)
++  for(auto iter = fn.begin(); iter != fn.end(); ++iter)
+   {
+-    NodeId wid = (int)fn[i]["wordId"];
+-    NodeId nid = (int)fn[i]["nodeId"];
++    NodeId wid = (int)(*iter)["wordId"];
++    NodeId nid = (int)(*iter)["nodeId"];
+
+     m_nodes[nid].word_id = wid;
+     m_words[wid] = &m_nodes[nid];