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ros-planning / navigation_experimental

Experimental navigation techniques for ROS robots.

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Backward and turn motion primitives

LotfiZ opened this issue · comments

commented

Hi folks,

I dont know if its relevant to ask this here so please close the issue if not.

I wanted to generate motion primitives using the Matlab script genmprim_unicycle.m and i was not able to generate a particular motion that is : backward and turn. I dont know why because i thought its just the opposite of the forward and turn motion, this is my setup :

%0 degreees  
    basemprimendpts0_c = zeros(numberofprimsperangle, 4); %x,y,theta,costmult   
    %x aligned with the heading of the robot, angles are positive  
    %counterclockwise  
    %0 theta change  
    basemprimendpts0_c(1,:) = [1 0 0 forwardcostmult];  
    basemprimendpts0_c(2,:) = [8 0 0 forwardcostmult];  
    basemprimendpts0_c(3,:) = [-1 0 0 backwardcostmult];  
    %1/16 theta change  
    basemprimendpts0_c(4,:) = [8 1 1 forwardandturncostmult];  
    basemprimendpts0_c(5,:) = [8 -1 -1 forwardandturncostmult];  
    %backward and turn  
    basemprimendpts0_c(6,:) = [-8 -1 1 backwardandturncostmult];  
    basemprimendpts0_c(7,:) = [-8 1 -1 backwardandturncostmult];

And i obtained this for 0 degrees :
mprim

As you can see, forward and turn/backward and turn are not generated the same way. Do you have some idea about this ?

Thank you !

commented

That's not the full modified portion of the script. Please post your full modified script.

commented

Hi Martin, thank you for the quick reply. I did not post the full script because i just added the backward and turn motion into the original script : https://github.com/sbpl/sbpl/blob/4d654845aa3b92aa1b4282a342e9011bac95aeb9/matlab/mprim/genmprim_unicycle.m .
I had a quick look to the script that you provide and i think that the case why the genmprim_unicycle.m does not generate the backward and turn motion correctly is because of this condition (im not sure) : https://github.com/sbpl/sbpl/blob/4d654845aa3b92aa1b4282a342e9011bac95aeb9/matlab/mprim/genmprim_unicycle.m#L221
if l < 0 fprintf(1, 'WARNING: l = %d < 0 -> bad action start/end points\n', l); l = 0; end;

Thank you !