Question

I’m using OpenCV 2.4.2 and Point Cloud Library 1.6.0.

My program is working fine until I add the line…

#include <pcl/segmentation/segment_differences.h>

This causes errors when I try to compile. I get…

Error   93  error C2872: 'flann' : ambiguous symbol C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl\kdtree\kdtree_flann.h  424
Error   94  error C2872: 'flann' : ambiguous symbol C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl\kdtree\kdtree_flann.h  425
Error   95  error C2872: 'flann' : ambiguous symbol C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl\kdtree\kdtree_flann.h  427
Error   96  error C2872: 'flann' : ambiguous symbol C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl\kdtree\kdtree_flann.h  514
Error   97  error C2872: 'flann' : ambiguous symbol C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl\kdtree\kdtree_flann.h  520

C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl/kdtree/kdtree_flann.h(520): error C2872: 'flann' : ambiguous symbol
              could be 'flann'
              or       'cv::flann'

So it looks like the Flann files that come with OpenCV are getting a conflict with the Flann files in PCL.

Any suggestions?

Edit

There is a similar question here
PCL, OpenCV and flann conflict
but it’s a slightly different error…

Edit 2

so in my main.cpp file I previously had

using namespace pcl;
using namespace cv;

I commented these two out and updated the program to use cv::Mat etc.

but I still get errors during compile when I add…

#include <pcl/segmentation/segment_differences.h>

C:\Program Files (x86)\PCL 1.6.0\include\pcl-1.6\pcl/kdtree/kdtree_flann.h(520): error C2872: 'flann' : ambiguous symbol 
          could be 'flann' 
          or       'cv::flann'

I’ve just tried renaming include\opencv2\flann\ to include\opencv2\flanncv\ and updating the includes in a bunch of opencv headers to this new flanncv directory. I’m still getting the above error…

Answer 1

So a fix for this without having to rebuild things is to add a null namespace to it

change instances of
flann::something
to
::flann::something

I think it’s effectivly telling it to use the global namespace and not the cv namespace.