cartesian controller, help for attachTipFrame()

[valeriosperati]

Please, about cartesian controller (with icub simulator) I was trying the code here Defining a Different Effector.

Question 1: which headers should I include for class iCubFinger?
I tried them but I'm not sure:

#include <iCub/iKin/iKinFwd.h>
#include <iCub/iKin/iKinHlp.h>
#include <iCub/iKin/iKinInv.h>
#include <iCub/iKin/iKinIpOpt.h>
#include <iCub/iKin/iKinSlv.h>
#include <iCub/iKin/iKinVocabs.h>

Question 2: should I include some particular library in CMakeLists?
Right now, when I try to compile I get several undefined reference:

CMakeFiles/exe.dir/myIcub.cpp.o: In function `myIcub::initParam(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >)':         
myIcub.cpp:(.text+0x5678): undefined reference to `iCub::iKin::iCubFinger::iCubFinger(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
myIcub.cpp:(.text+0x763b): undefined reference to `vtable for iCub::iKin::iCubFinger'
myIcub.cpp:(.text+0x76a8): undefined reference to `iCub::iKin::iKinLimb::~iKinLimb()'
CMakeFiles/exe.dir/myIcub.cpp.o: In function `iCub::iKin::iCubFinger::~iCubFinger()':
myIcub.cpp:(.text._ZN4iCub4iKin10iCubFingerD2Ev[_ZN4iCub4iKin10iCubFingerD5Ev]+0x3): undefined reference to `vtable for iCub::iKin::iCubFinger'
myIcub.cpp:(.text._ZN4iCub4iKin10iCubFingerD2Ev[_ZN4iCub4iKin10iCubFingerD5Ev]+0x5f): undefined reference to `iCub::iKin::iKinLimb::~iKinLimb()'
CMakeFiles/exe.dir/myIcub.cpp.o: In function `iCub::iKin::iCubFinger::~iCubFinger()':
myIcub.cpp:(.text._ZN4iCub4iKin10iCubFingerD0Ev[_ZN4iCub4iKin10iCubFingerD5Ev]+0x3): undefined reference to `vtable for iCub::iKin::iCubFinger'
myIcub.cpp:(.text._ZN4iCub4iKin10iCubFingerD0Ev[_ZN4iCub4iKin10iCubFingerD5Ev]+0x5e): undefined reference to `iCub::iKin::iKinLimb::~iKinLimb()'
collect2: error: ld returned 1 exit status
CMakeFiles/exe.dir/build.make:830: recipe for target 'exe' failed

I guess I need the proper library in TARGET_LINK_LIBRARIES, which currently is:

TARGET_LINK_LIBRARIES(exe ${OpenCV_LIBS} ${YARP_LIBRARIES} itpp Qt5::Widgets)

Thanks, Valerio

[pattacini]

Hi @valeriosperati

You ought to:

1. include iKinFwd.h
2. link against iKin, thus:

   find_package(ICUB REQUIRED)
   target_link_libraries(exe iKin)

[valeriosperati]

Perfect! Thanks

[valeriosperati]

Please, I need clarification about the use of code, in particular I'm comparing Defining a Different Effector and How to use the iCubFinger forward kinematics.

It is not clear to me if the following piece of code, computing the Matrix tipFrame

iencs->getEncoders(encs.data());
yarp::sig::Vector joints;
finger.getChainJoints(encs,joints);
yarp::sig::Matrix tipFrame=finger.getH((M_PI/180.0)*joints);

Vector tip_x=tipFrame.getCol(3);
Vector tip_o=yarp::math::dcm2axis(tipFrame);
icart->attachTipFrame(tip_x,tip_o); 

must be used only once, during initialisation of cartesian controller, or if I need to recompute it everytime before a call to
icart->goToPose(xd,od);

As I read here, the helper method getChainJoints() is based on the values of encoders, so I was wondering if I need to refresh it -through a call to iencs->getEncoders(encs.data())- before each new cartesian command.
Thanks

[pattacini]

Anytime you move the finger's joints, then you have to update the matrix tipFrame and let the Cartesian Controller know about that.

In practice, this won't happen so often, thereby the workflow could be:

1. Put the finger in the configuration whose tip you'd like to control.
2. Read the finger's joints once (making sure you'll obtain a fresh update).
3. Compute the matrix tipFrame.
4. Call attachTipFrame only once.
5. Run your control by calling goToPose as many times as you need, in the assumption that the finger won't move.
6. Remember to restore the default control point by means of removeTipFrame (or through context switching).

[valeriosperati]

Ok, so if I have to recompute for some reason the index finger joints, I have to redo all the steps you say, right?.
A last question: in this last case do I have to call removeTipFrame() before calling again AttachTipFrame()?
Thanks

[pattacini]

1. Yep 👍
2. Nope, you can skip the removeTipFrame and proceed straight to attachTipFrame.

[valeriosperati]

Thanks!
Valerio