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 Post subject: Detect elliptical parts in a 2d laserscan
PostPosted: Mon Jun 11, 2012 1:24 pm 
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Joined: Mon May 14, 2012 4:35 pm
Posts: 5
Hi,

I have to write a C++ Programm which is able to detect an elliptical part in a 2d laserscan.
My scaner gives x,y Data from the scene.
The next step after i have detected the elliptical Part is to say from which area of an completely elliptic circumference the detected part is.
I have breake down the Scan into segments which i check with the alglib::lsfitlinear().
But i think lsfitlinear is not the right method for this task because much segments of even lines are detected as an elliptical part. The sample data for lsfitlinear came from a scan segment representing the ellipse i'm searching for.
Now i have no idea how to continue or which method is the right for this task.
Here my code:
Code:
alglib::ae_int_t info;
   alglib::ae_int_t M = 1;
   alglib::real_1d_array c;
   alglib::lsfitreport rep;

   alglib::real_2d_array sample;
   alglib::real_1d_array experimentalData;

   //create segment from file
   Segment seg = this->createSampleSegmentFromFile("./samples/sample.txt", 130);

   //translate sample in the origin
   double avgXdist = this->calcAvgXDistance(seg);
   double avgYdist = this->calcAvgYDistance(seg);
   this->transformer->translateSegment(seg, -avgXdist, -avgYdist);
   
   //create real_2d_array sample
   sample = this->createReal2DArrayFromSegment(seg);

   Segment s;
   ScanPoint p1;
   ScanPoint p2;

   
   for (int i = 0; i < scan->getSegments()->size(); i++)
   {
      s = scan->getSegments()->at(i);

      p1 = s.getSegmentPoints()->at(0);
      p2 = s.getSegmentPoints()->at(s.getSegmentPoints()->size() - 1);

      s.setAvgDist(this->calcAvgDistance(s));
      s.setEuclidainDist(this->calcEuclidDist(p1, p2));

      //translate segment to be examined in the origin
      double avgSegXdist = this->calcAvgXDistance(s);
      double avgSegYdist = this->calcAvgYDistance(s);
      this->transformer->translateSegment(s, -avgSegXdist, -avgSegYdist);

      //create experimental data array
      experimentalData = this->createReal1DArrayFormSegment(s);
      
      //do fitting
      if (experimentalData.length() <= sample.rows()
         && s.getAvgDist() <= 6000
         && s.getAvgDist() >= 1500
         && s.getEuclidianDist() <= 1800)
      {

         //rotate Segment 360°
         for (int j = 0; j < 36; j++)
         {
         
            alglib::lsfitlinear(experimentalData, sample, experimentalData.length(),
               M, info, c, rep);
   
            //rotiere um 10°
            this->transformer->rotateSegment(s, 10);

            //std::cout<<"Fitting by: " << j << "°" << "\n";
         }

         scan->getSegments()->at(i).setAvgErr(rep.avgerror);
         scan->getSegments()->at(i).setMaxErr(rep.maxerror);

         if (scan->getSegments()->at(i).getAvgErr() < 150)
         {
            scan->getSegments()->at(i).setIsStation(true);
         }

         std::cout<<"is station: "<<scan->getSegments()->at(i).getIsStation()<<"\n";
         std::cout<<"SegNr: " << i << "  AvgERR: "<<rep.avgerror <<"\n";
         std::cout<<"SegNr: " << i << "  MaxERR: "<<rep.maxerror <<"\n";
         std::cout<<"euclid Dist: " << s.getEuclidianDist() <<"\n";
      }
      else
      {
         std::cout<<"Segment NR: "<< i <<  "is to large" <<"\n\n";
      }
   }


PLEASE HELP! -.-


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 Post subject: Re: Detect elliptical parts in a 2d laserscan
PostPosted: Tue Jun 12, 2012 8:11 am 
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Site Admin

Joined: Fri May 07, 2010 7:06 am
Posts: 878
Can you post some pictures which illustrate your problem? It is hard to understand specifics without graphical representation.


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 Post subject: Re: Detect elliptical parts in a 2d laserscan
PostPosted: Tue Jun 12, 2012 9:49 am 
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Joined: Mon May 14, 2012 4:35 pm
Posts: 5
Hi,

many thanks for your very quick answer.
Here some pics to illustrate my problem and the results.
The sample.png represents the real_2d_array "sample" in my code. It is recorded with a minimum distance so that it gets maximal amount of x,y Points for fitting.
The fittingResult.png shows the result of lsfitlinear(). If the avgErr for an Segment is < 150 i estimate that this segment is an elliptical part an painted red. But as you can see the straight line is also an elliptical part and has even an avgErr < 30, but why?
The faildetect.png shows some more wrong detected segments.
Perhabs it is because i do some transformations on the segments but without these transformations i got worse results.

best regards
christian


Attachments:
faildetect.png
faildetect.png [ 8.21 KiB | Viewed 4007 times ]
fittingResult.png
fittingResult.png [ 12.29 KiB | Viewed 4007 times ]
sample.png
sample.png [ 3.72 KiB | Viewed 4007 times ]
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 Post subject: Re: Detect elliptical parts in a 2d laserscan
PostPosted: Mon Jun 18, 2012 8:29 am 
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Joined: Mon May 14, 2012 4:35 pm
Posts: 5
nobody any idea?


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