simxReadProximitySensor not working on python & matlab

[Space]

Hi,

I am using matlab and python to simulate the navigation of my robot a pioneer p3dx.
for this, i added a Sick 2D laser on the robot but each time i try to get the data from it it returns 0.

before you ask, the connection with Vrep is working as i get the handle value of the laser and my version of python is 2.7 and matlab 2010, see below :

Code: Select all

[~,laserScannerHandle] = vrep.simxGetObjectHandle(clientID,'LaserScanner_2D',vrep.simx_opmode_oneshot_wait); 
for t =1:0.1:200
     [~,detectionState,detectedPointL,detectedObjectHandle,detectedSurfaceNormalVector] = vrep.simxReadProximitySensor(clientID,laserScannerHandle,vrep.simx_opmode_streaming);
     [~,detectionState,detectedPointL,detectedObjectHandle,detectedSurfaceNormalVector] = vrep.simxReadProximitySensor(clientID,laserScannerHandle,vrep.simx_opmode_buffer)

thank you for your replay

[coppelia]

You have several problems. The first is that object LaserScanner_2D is not a proximity sensor! It is a shape.

Then, ALWAYS check the first return value, that will tell you if some sort of error happended, or if a time-out happended.

Finally, since your laser scanner is scanning several points in a second, if you try to read the proximity sensor as you are doing it, you will only get very sparse data. The best to do is to pack all the points for an entire scan into a string signal, and read that string signal from the Matlab side.

Cheers

[Space]

Hi,

thank you for your replay.
May i ask you what are the functions to use? i am a bit new on manipulating Vrep.

thanks in advance!

[coppelia]

On V-REP side, try with simPackFloats and simSetStringSignal. On the Matlab side, use simxGetStringSignal and simxUnpackFloats.

Cheers

[Space]

Hi Coppelia,

i tried to run the code

on the Vrep side :

Code: Select all

	laserScannerHandle=simGetObjectHandle("LaserScanner_2D")
	laserScannerObjectName=simGetObjectName(laserScannerHandle)
	communicationTube=simTubeOpen(0,laserScannerObjectName..'_2D_SCANNER_DATA',1)
	
	data=simTubeRead(communicationTube)
        if (data) then
	    laserDetectedPoints=simUnpackFloats(data)
	end

on the matlab side :

Code: Select all

[~,data] = vrep.simxGetStringSignal(clientID,'data',vrep.simx_opmode_streaming)
          if (data)
       laserDetectedPoints= vrep.simUnpackFloats(data);
	end

getting through the docs, i am not sure how to get the signal on simxGetStringSignal

thanks for your help

[coppelia]

The simplest is to put something like that in the code that generates the sensor points:

Code: Select all

if (sim_call_type==sim_childscriptcall_sensing) then 

...

	if #points>0 then
		local ptsPacked=simPackFloats(points)
		simSetStringSignal("myPts",ptsPacked)
	else
		simClearStringSignal("myPts")
	end
end

and on the Matlab side:

Code: Select all

[res,data]=vrep.simxGetStringSignal(clientID,'myPts',vrep.simx_opmode_buffer)
...

Make sure you understand how to use data streaming with the remote API.

Cheers

[Space]

Hi coppelia,

after applying the program, I get an error message :

Lua API call error: [string "SCRIPT LaserScanner_2D"]:64: One of the function's argument type is not correct. (simSetFloatSignal)

it seems like MyPts is note defined.

I am a bit lost!!!

Thanks

[coppelia]

Sorry, made a mistake in my previous post, but corrected it now. Basically it should be simSetStringSignal, not simSetFloatSignal, and simClearStringSignal, not simClearFloatSignal.

Sorry about that.

[Space]

Thank you!

I will try it

[Space]

Hi again,

on the matlab side :

Code: Select all

[~,data]=vrep.simxGetStringSignal(clientID,'myPts',vrep.simx_opmode_buffer);
    
    [data]=simxUnpackFloats(data) 

still don't get my data!!