https://github.com/OctoMap/octomap/pull/433.patch
switch qt4/qt5 to qt5/qt6
qt6 just works as is
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f1eb31f3..6a4db7eb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,7 +6,7 @@ set(CMAKE_POSITION_INDEPENDENT_CODE ON)  # enables -fPIC in applicable compilers
 
 option(BUILD_OCTOVIS_SUBPROJECT "Build targets from subproject octovis" ON)
 option(BUILD_DYNAMICETD3D_SUBPROJECT  "Build targets from subproject dynamicEDT3D" ON)
-option(OCTOVIS_QT5 "Link Octovis against Qt5?" ON)
+option(OCTOVIS_QT6 "Link Octovis against Qt6?" ON)
 
 set(CMAKE_CXX_STANDARD 11)
 
diff --git a/octovis/CMakeLists.txt b/octovis/CMakeLists.txt
index 84fa3675..e6dd604c 100644
--- a/octovis/CMakeLists.txt
+++ b/octovis/CMakeLists.txt
@@ -65,17 +65,14 @@ set(INSTALL_TARGETS_DEFAULT_ARGS
 # libQGLViewer, if dependencies available
 SET( BUILD_VIEWER 0)
 
-option(OCTOVIS_QT5 "Link Octovis against Qt5?" ON)
+option(OCTOVIS_QT6 "Link Octovis against Qt6?" ON)
 
 # Look for required libraries:
 set(OpenGL_GL_PREFERENCE LEGACY)
 FIND_PACKAGE(OpenGL)
-if(NOT OCTOVIS_QT5)
-  FIND_PACKAGE(Qt4)
-endif(NOT OCTOVIS_QT5)
 
-IF (OpenGL-NOTFOUND OR Qt4-NOTFOUND)
-	MESSAGE ( "OpenGL and QT4 are required for octovis but could not be found.")
+IF (OpenGL-NOTFOUND)
+	MESSAGE ( "OpenGL is required for octovis but could not be found.")
 ELSE()
 	FIND_PACKAGE(QGLViewer)
 	IF(QGLViewer_FOUND)
diff --git a/octovis/CMakeLists_src.txt b/octovis/CMakeLists_src.txt
index 35bc1f20..6eaa31ad 100644
--- a/octovis/CMakeLists_src.txt
+++ b/octovis/CMakeLists_src.txt
@@ -1,5 +1,8 @@
 
-if(OCTOVIS_QT5)
+if(OCTOVIS_QT6)
+  find_package(Qt6 REQUIRED COMPONENTS Core Gui OpenGLWidgets Widgets Xml)
+  set(QT_LIBRARIES Qt6::Core Qt6::Gui Qt6::OpenGLWidgets Qt6::Widgets Qt6::Xml "${OPENGL_gl_LIBRARY}" "${OPENGL_glu_LIBRARY}")
+else(OCTOVIS_QT6)
   find_package(Qt5Core REQUIRED)
   find_package(Qt5Gui REQUIRED)
   find_package(Qt5OpenGL REQUIRED)
@@ -13,14 +16,7 @@ if(OCTOVIS_QT5)
     "${Qt5Widgets_INCLUDE_DIRS}"
     "${Qt5Xml_INCLUDE_DIRS}"
     )
-else(OCTOVIS_QT5)
-  # Qt4-support (more info: http://qtnode.net/wiki?title=Qt_with_cmake)
-  find_package(Qt4 REQUIRED)
-  set(QT_USE_QTOPENGL TRUE)
-  set(QT_USE_QTXML TRUE)
-  # include the files enabled above
-  include(${QT_USE_FILE})
-endif(OCTOVIS_QT5)
+endif(OCTOVIS_QT6)
 
 # Mac OS X seems to require special linker flags:
 IF(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
@@ -51,11 +47,11 @@ set(viewer_SRCS
 )	
 
 # Resource files (icons, ...)
-if(OCTOVIS_QT5)
+if(OCTOVIS_QT6)
+  QT6_ADD_RESOURCES(viewer_RES src/icons.qrc)
+else(OCTOVIS_QT6)
   QT5_ADD_RESOURCES(viewer_RES src/icons.qrc)
-else(OCTOVIS_QT5)
-  QT4_ADD_RESOURCES(viewer_RES src/icons.qrc)
-endif(OCTOVIS_QT5)
+endif(OCTOVIS_QT6)
 
 #found QGLViewer lib dir
 link_directories(${QGLViewer_LIBRARY_DIR})
@@ -74,11 +70,11 @@ SET(viewer_MOC_HDRS
 )
 
 # generate list of MOC srcs:
-if(OCTOVIS_QT5)
+if(OCTOVIS_QT6)
+  QT6_WRAP_CPP(viewer_MOC_SRCS ${viewer_MOC_HDRS})
+else(OCTOVIS_QT6)
   QT5_WRAP_CPP(viewer_MOC_SRCS ${viewer_MOC_HDRS})
-else(OCTOVIS_QT5)
-  QT4_WRAP_CPP(viewer_MOC_SRCS ${viewer_MOC_HDRS})
-endif(OCTOVIS_QT5)
+endif(OCTOVIS_QT6)
 
 # let cmake generate ui*.h files from .ui files (Qt Designer):
 SET(viewer_UIS
@@ -87,11 +83,11 @@ SET(viewer_UIS
     ${PROJECT_SOURCE_DIR}/include/octovis/ViewerSettingsPanel.ui
     ${PROJECT_SOURCE_DIR}/include/octovis/ViewerSettingsPanelCamera.ui
 )
-if(OCTOVIS_QT5)
+if(OCTOVIS_QT6)
+  QT6_WRAP_UI(viewer_UIS_H ${viewer_UIS})
+else(OCTOVIS_QT6)
   QT5_WRAP_UI(viewer_UIS_H ${viewer_UIS})
-else(OCTOVIS_QT5)
-  QT4_WRAP_UI(viewer_UIS_H ${viewer_UIS})
-endif(OCTOVIS_QT5)
+endif(OCTOVIS_QT6)
 
 # Don't forget to include output directory, otherwise
 # the UI file won't be wrapped!
@@ -101,6 +97,7 @@ include_directories(${CMAKE_CURRENT_BINARY_DIR} ${CMAKE_BINARY_DIR})
 # Library target 
 add_library(octovis-static STATIC ${viewerlib_SRCS})
 target_link_libraries(octovis-static
+  ${QT_LIBRARIES}
   ${OPENGL_gl_LIBRARY} 
   ${OPENGL_glu_LIBRARY} 
   ${OCTOMAP_LIBRARIES}
@@ -110,6 +107,7 @@ set_target_properties(octovis-static PROPERTIES OUTPUT_NAME octovis)
 
 add_library(octovis-shared SHARED ${viewerlib_SRCS})
 target_link_libraries(octovis-shared 
+  ${QT_LIBRARIES}
   ${OPENGL_gl_LIBRARY} 
   ${OPENGL_glu_LIBRARY} 
   ${OCTOMAP_LIBRARIES}
@@ -135,7 +133,6 @@ add_executable(octovis ${viewer_SRCS} ${viewer_UIS_H} ${viewer_MOC_SRCS} ${viewe
 
 target_link_libraries(octovis 
 #  ${QGLViewer_LIBRARIES}
-  ${QT_LIBRARIES}
   ${OCTOMAP_LIBRARIES}
   octovis-shared
 )