void graph2D_mod1()

{
   TCanvas *c = new TCanvas("c","Graph2D example",0,0,700,600);
   Double_t x, y, z, P = 15.;
   Int_t np = 100;
   TGraph2D *graph = new TGraph2D();
   TRandom *r = new TRandom();
  //Int_t const m[10], n[10],p[10];
  //Int_t *m;
   for (Int_t N=0; N<np; N++) {
      x = 2*P*(r->Rndm(N))-P;
      y = 2*P*(r->Rndm(N))-P;
      
      z=0; // setting z=0 causes problem with 3d graphics.
     // z=1.0; // this is ok, but is not ideal suitable for 2D image segmentation
      
      graph->SetPoint(N,x,y,z);
   }
  // gStyle->SetPalette(1);

     graph->Draw("TRIW");
     c->Update();
     
}