Hi Ruben,

> From looking at the code I do not see how this can happen. Can you provide
us all the code including the creation of both solvers and the calls to the
forward kinematics.

This is my main.cpp:

#include <chain.hp

#include <chainfksolver.hp

#include <chainfksolverpos_recursive.hp

#include <frames_io.hp

#include <stdio.h>
#include <iostream>

using namespace KDL;

void solve( KDL::Chain& chain )
{
// Create solver based on kinematic chain
ChainFkSolverPos_recursive fksolver = ChainFkSolverPos_recursive(chain);

// Create joint array
unsigned int nj = chain.getNrOfJoints();
KDL::JntArray jointpositions = JntArray(nj);

// Assign some values to the joint positions
for(unsigned int i=0;i<nj;i++){
jointpositions(i)=(double)i;
}

// Create the frame that will contain the results
KDL::Frame cartpos;

// Calculate forward position kinematics
bool kinematics_status;
kinematics_status = fksolver.JntToCart(jointpositions,cartpos);
if(kinematics_status>=0){
std::cout << cartpos <<std::endl;
printf("%s \n","Succes, thanks KDL!");
}else{
printf("%s \n","Error: could not calculate forward kinematics :(");
}
}

int main( int argc, char** argv )
{
//Definition of a kinematic chain & add segments to the chain
KDL::Chain chain;

chain.addSegment(Segment(Joint(Joint::RotZ),Frame(Vector(0.0,0.0,1.020))));

chain.addSegment(Segment(Joint(Joint::RotX),Frame(Vector(0.0,0.0,0.480))));

chain.addSegment(Segment(Joint(Joint::RotX),Frame(Vector(0.0,0.0,0.645))));
chain.addSegment(Segment(Joint(Joint::RotZ)));

chain.addSegment(Segment(Joint(Joint::RotX),Frame(Vector(0.0,0.0,0.120))));
chain.addSegment(Segment(Joint(Joint::RotZ)));

std::cout << std::endl << "Chain without offsets:" << std::endl;
solve(chain);

//Definition of a kinematic chain & add segments to the chain
KDL::Chain chain2;
chain2.addSegment(Segment(Joint(Joint::RotZ, 1.0,
1.0),Frame(Vector(0.0,0.0,1.020))));
chain2.addSegment(Segment(Joint(Joint::RotX, 1.0,
2.0),Frame(Vector(0.0,0.0,0.480))));
chain2.addSegment(Segment(Joint(Joint::RotX, 1.0,
3.0),Frame(Vector(0.0,0.0,0.645))));
chain2.addSegment(Segment(Joint(Joint::RotZ, 1.0, 4.0)));
chain2.addSegment(Segment(Joint(Joint::RotX, 1.0,
5.0),Frame(Vector(0.0,0.0,0.120))));
chain2.addSegment(Segment(Joint(Joint::RotZ, 1.0, 6.0)));

std::cout << std::endl << "Chain with offsets:" << std::endl;
solve(chain2);
}

The output is

Chain without offsets:
[[ -0.369277, -0.923162, -0.1068;
0.472269, -0.285396, 0.833973;
-0.800373, 0.257528, 0.541371]
[ -0.012816, -0.394852, 0.705764]]
Succes, thanks KDL!

Chain with offsets:
[[ -0.369277, -0.923162, -0.1068;
0.472269, -0.285396, 0.833973;
-0.800373, 0.257528, 0.541371]
[ -0.012816, -0.394852, 0.705764]]
Succes, thanks KDL!

I am using Orocos KDL revision 3d6b7c225cb7 from the repository (created by
you with the comment "cmake: make sure PyKDL gets intalled in the right
directory, not super robust though") and g++ 4.6.2 with MinGW, but the
effect was the same when I tried VC 2008 Express.

Thank you for your answer!

Bye,
Benjamin

>

Hi Benjamin,

On Fri, Aug 17, 2012 at 7:00 AM, Benjamin Bihler
<benjamin [dot] bihler [..] ...> wrote:
> Hi Ruben,
>
> did you find time to look at my example. Does it show the same behavior on
> your system? Thanks!

I have found some time to look at it, and I can confirm that this is a
bug. I think I have an idea where it comes from (segment.cpp,
calculation of f_tip at construction time) But I have not found a
solution for it yet.

> Bye,
> Benjamin

Ruben

>
> -----Ursprüngliche Nachricht-----
> Von: ruben [dot] smits [..] ... [mailto:ruben [dot] smits [..] ...]
> Im Auftrag von Ruben Smits
> Gesendet: Dienstag, 14. August 2012 11:45
> An: Benjamin Bihler
> Cc: orocos-users [..] ...
> Betreff: Re: [Orocos-users] KDL Joint offsets do not work
>
> Hi Benjamin,
>
> On Thu, Aug 2, 2012 at 9:25 AM, Benjamin Bihler
> <benjamin [dot] bihler [..] ...> wrote:
>>
>> Hi,
>>
>> I have the feeling that the offsets in the joints of KDL kinematic
>> chains do not work. If I modify the forward kinematic chain example
>> from http://www.orocos.org/kdl/examples to define the chain like this
>>
>> //Definition of a kinematic chain & add segments to the chain
>> KDL::Chain chain;
>> chain.addSegment(Segment(Joint(Joint::RotZ, 1.0,
>> 1.0),Frame(Vector(0.0,0.0,1.020))));
>> chain.addSegment(Segment(Joint(Joint::RotX, 1.0,
>> 2.0),Frame(Vector(0.0,0.0,0.480))));
>> chain.addSegment(Segment(Joint(Joint::RotX, 1.0,
>> 3.0),Frame(Vector(0.0,0.0,0.645))));
>> chain.addSegment(Segment(Joint(Joint::RotZ, 1.0, 4.0)));
>> chain.addSegment(Segment(Joint(Joint::RotX, 1.0,
>> 5.0),Frame(Vector(0.0,0.0,0.120))));
>> chain.addSegment(Segment(Joint(Joint::RotZ, 1.0, 6.0)));
>>
>> and if I then enter the same joint positions as before, the result is
>> exactly the same. Shouldn’t it be different? I expected it to be as if
>> I had added 1 to the first joint position, 2 to the second one and so
>> on. Did I miss anything?
>
> From looking at the code I do not see how this can happen. Can you provide
> us all the code including the creation of both solvers and the calls to the
> forward kinematics.
>
>
> Ruben
>
>> Thank you for your help!
>>
>>
>> Benjamin
>>
>> --
>> Orocos-Users mailing list
>> Orocos-Users [..] ...
>> http://lists.mech.kuleuven.be/mailman/listinfo/orocos-users
>
>
>
>
> --
> Ruben Smits, Phd
> Chief Technology Officer
> Intermodalics BVBA
> +32479511786
> www.intermodalics.eu
>

On Aug 14, 2012, at 03:23 , Benjamin Bihler wrote:

> Hello,
>
> may I ask again: does anyone use the KDL joint offsets (i.e. define offsets different from zero) in combination with forward/inverse kinematics solvers? As far as I understand their definition, the results should change if I set offsets during the definition of the kinematic chain. But this is not the case here.
>
> I have debugged into the KDL::Joint::pose method and the offsets there are definitely different from zero. Therefore why do I get exactly the same results as if the offsets were zero?

Do you have a test case you can provide us, that demonstrates this?
S