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How to make a boost::shared_ptr<T> for global var

asked 2013-03-12 10:17:36 -0500

MartinW gravatar image

updated 2013-03-12 10:20:24 -0500

Hello all,

I was wondering how to create a boost::shared_ptr<T> global variable for a tf::TransformListener object? I am encountering the same problem as in this question posted a while ago but I don't know enough about boost::shared_ptr<T>.

Can someone explain how I can declare and initialize boost::shared_ptr<T> with respect to tf::TransformListener? Many thanks in advance.

Kind Regards, Martin

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answered 2013-03-12 10:31:15 -0500

Hi Martin,

boost::shared_ptr<tf::TransformListener> tf_ptr;

...

int main(int argc, const char* argv []) {

  ros::init(argc, argv, "my_node");
  tf_ptr.reset(new tf::TransformListener);

  ... do more stuff here. Use tf_ptr as a regular pointer for the most part ...

  return 0;
}

The comments in this thread also explain the same answer.

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Thanks for the quick reply piyushk! I tried this but now I am back to getting the error: reference to ‘transform’ is ambiguous. candidates are: tf::StampedTransform transform. Do I need to make StampedTransform a shared_ptr too? the variable transform is what I need in my callback

MartinW gravatar image MartinW  ( 2013-03-12 10:47:15 -0500 )edit

Can you give the code sample producing that.

dornhege gravatar image dornhege  ( 2013-03-12 10:53:33 -0500 )edit

Hey dornhege, I put the code into another answer (forgetting that I could edit my own question haha)

MartinW gravatar image MartinW  ( 2013-03-12 11:05:27 -0500 )edit
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answered 2013-03-12 11:02:54 -0500

MartinW gravatar image

updated 2013-03-12 11:09:25 -0500

Hey @dornhege and @piyushk,

Thanks for taking the time to reply to my questions! However, I am still getting some errors so I am just going to post a little bit of my code here and maybe you can help me fix the problems.

So my global variables for the transform are:

tf::StampedTransform transform;
boost::share_ptr<tf::TransformListener> transform_ptr;

Then I have my

int main (int argc, char** argv)
{

ros::init (argc, argv, "SitAssessManager");

transform_ptr.reset(new tf::TransformListener);
ros::NodeHandle n;

try{
transform_ptr->waitForTransform("/base_link","/camera_depth_optical_frame",ros::Time::now(),ros::Duration(3));
        transform_ptr->lookupTransform("/base_link", "/camera_depth_optical_frame",ros::Time::now(), transform);
        }
    catch (tf::TransformException ex){
        ROS_WARN("Base to camera transform unavailable %s", ex.what());
        }

while(n.ok())
{
ros::spinOnce();
loop_rate.sleep();
}

Where in my Kinect frames callback I use a vector3f point and use transform to go from the frame to frame just by: t_point = transform*point;

Here is the compiling error:

 In function ‘void callback(const PointCloud2ConstPtr&)’:
  /martin/ros_workspace/SituationAssessmentManager/src/H20.cpp:559:13: error: reference to ‘transform’ is ambiguous
  /martin/ros_workspace/SituationAssessmentManager/src/H20.cpp:80:22: error: candidates are: tf::StampedTransform transform
  /usr/include/c++/4.6/bits/stl_algo.h:4907:5: error:                 template<class _IIter1, class _IIter2, class _OIter, class _BinaryOperation> _OIter std::transform(_IIter1, _IIter1, _IIter2, _OIter, _BinaryOperation)
  /usr/include/c++/4.6/bits/stl_algo.h:4871:5: error:                 template<class _IIter, class _OIter, class _UnaryOperation> _OIter std::transform(_IIter, _IIter, _OIter, _UnaryOperation)
  /martin/ros_workspace/SituationAssessmentManager/src/H20.cpp:718:96: error: reference to ‘transform’ is ambiguous
  /martin/ros_workspace/SituationAssessmentManager/src/H20.cpp:80:22: error: candidates are: tf::StampedTransform transform

So the error shows up from both calls to 'transform', once in the callback and once in main

Thanks again!

Kind Regards, Martin

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Comments

@martin: Can you post a link to the entire file? This is a pretty nasty error.

piyushk gravatar image piyushk  ( 2013-03-12 19:59:38 -0500 )edit

Do you have a using namespace std; anywhere? In any case: renaming transform to something else should fix that error.

dornhege gravatar image dornhege  ( 2013-03-13 01:00:49 -0500 )edit

Yea, I had using namespace std; before I declared it. After I changed the name, it fixed the error! Thanks for all the help!

MartinW gravatar image MartinW  ( 2013-03-14 07:57:05 -0500 )edit
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answered 2013-03-12 10:26:31 -0500

dornhege gravatar image

You should only encounter the problem if you create the pointer before calling ros::init(). The shared pointer itself should not create any TransformListener on its own.

So, the new to be put in the shared_ptr needs to come after ros::init.

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Well, I have it set as a global variable at the top of my program: <tf::TransformListener> listener and <tf::TransformListener> transform. Then I have a function called getTransform() where I run the transformation code listener.waitForTransform and listener.lookupTransform ... continued

MartinW gravatar image MartinW  ( 2013-03-12 10:31:36 -0500 )edit

Then for my main() I run init first just like every other program I've made and I make a call to getTransform() right before entering a while(n.ok()) loop where the callback uses the global transform variables. I'm not using any pointers now because I don't understand how to use the them

MartinW gravatar image MartinW  ( 2013-03-12 10:33:13 -0500 )edit

If it's static variables and not pointers, you'll get exactly the problems that you have. See the answer by @piyushk for a shared_ptr sample.

dornhege gravatar image dornhege  ( 2013-03-12 10:52:02 -0500 )edit

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Asked: 2013-03-12 10:17:36 -0500

Seen: 2,921 times

Last updated: Mar 12 '13