Creating a better contour plot

fabstr · August 20, 2021, 10:10am

Please read tips for efficient and successful posting and posting code

ROOT Version: 6.22/00
Platform: Ubuntu 20.04.1 LTS (WSL2)
Compiler: GNU or GCC

Hello,
I have created a contour plot of the magnetic flux density of an octupole magnet. But I think there is a better way to do it. My code is little bit messy and I want my plot to show the contour line of the magnetic field by a radial distance less than 50 mm. My code is shown below and I want to improve the code so that my contour plot can become much simpler to interpret. I have two x and y positions and the magnetic field flux (B_mag = sqrt(B_x^2 + B_y^2 + B_z^")) that I want to plot.

#include "TFile.h"
#include "TTree.h"
#include "TCanvas.h"
#include "TH1F.h"
#include <iostream>

using namespace std;


void Contour_Plot(){

const Int_t NRGBs = 5;
  const Int_t NCont = 99;

  Double_t stops[NRGBs] = { 0.00, 0.34, 0.61, 0.84, 1.00 };
  Double_t red[NRGBs]   = { 0.00, 0.00, 0.87, 1.00, 0.51 };
  Double_t green[NRGBs] = { 0.00, 0.81, 1.00, 0.20, 0.00 };
  Double_t blue[NRGBs]  = { 0.51, 1.00, 0.12, 0.00, 0.00 }; 
  TColor::CreateGradientColorTable(NRGBs, stops, red, green, blue, NCont);   
  gStyle->SetNumberContours(NCont);
  
  TGraph2D *g=new TGraph2D("Test_data.txt","%lg %lg %lg");
  	
  g->SetNpx(200);
  g->SetNpy(200);
  g->SetTitle("Contour plot of the magnetic flux density (T) in the x-y plane");
  g->GetHistogram()->GetXaxis()->SetTitle("x (m)");
  g->GetHistogram()->GetYaxis()->SetTitle("y (m)");
  TCanvas *c = new TCanvas("c", "c");
  g->SetLineColor(kWhite);
  g->SetLineWidth(1);
  g->SetLineStyle(1);
  g->Draw("COLZ CONT3");
  g->GetHistogram()->GetYaxis()->SetRangeUser(-50.0, 50.0);
  g->GetHistogram()->GetXaxis()->SetRangeUser(-50.0, 50.0);
  c->SetRealAspectRatio();
  c->Modified(); c->Update();
   
   gPad->Update();
}

couet · August 20, 2021, 10:47am

Can you also post Test_data.txt ?

fabstr · August 20, 2021, 11:40am

Sure,
the first and second column is the x and y positions. The third, fourth and fifth columns are the magnetic field in the x,y and z directions. I reduced all the data due to the limited size that can be allowed here.

-0.0540000000000000	-0.0540000000000000	1.8540000000000001	2.1671304156105324	2.1671337870455591	0.6314719501482401
-0.0540000000000000	-0.0440000000000000	1.8540000000000001	1.1681125191097685	2.0362095130334983	0.6498627194105220
-0.0540000000000000	-0.0340000000000000	1.8540000000000001	0.3727889845003144	1.7396170659902923	0.6635834512715635
-0.0540000000000000	-0.0240000000000000	1.8540000000000001	-0.2186941242957418	1.3151506489580644	0.6732812742968249
-0.0540000000000000	-0.0140000000000000	1.8540000000000001	-0.6062520496906045	0.8004806203684057	0.6794100800985956
-0.0540000000000000	-0.0040000000000000	1.8540000000000001	-0.7898391311537749	0.2332117708771450	0.6822525940713834
-0.0540000000000000	0.0060000000000000	1.8540000000000001	-0.7694363593058535	-0.3490819919563398	0.6819384596644275
-0.0540000000000000	0.0160000000000000	1.8540000000000001	-0.5450460651273676	-0.9088346736663232	0.6784534261235351
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0.0160000000000000	0.0260000000000000	1.8540000000000001	-0.2317972573193159	-0.1020502569780614	0.7113848496969191
0.0160000000000000	0.0360000000000000	1.8540000000000001	-0.4192075473519968	-0.0016584690604614	0.7028151074653066
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0.0360000000000000	-0.0140000000000000	1.8540000000000001	0.0391475006763130	0.3720607773919850	0.7036627864866746
0.0360000000000000	-0.0040000000000000	1.8540000000000001	0.1615663010481042	0.1108086056023269	0.7061801224753511
0.0360000000000000	0.0060000000000000	1.8540000000000001	0.1479650884067642	-0.1654600424297698	0.7059018421385806
0.0360000000000000	0.0160000000000000	1.8540000000000001	-0.0016554581134653	-0.4192051344932485	0.7028154132756816
0.0360000000000000	0.0260000000000000	1.8540000000000001	-0.2872856989462327	-0.6128791322493964	0.6967805800408962
0.0360000000000000	0.0360000000000000	1.8540000000000001	-0.7089037496163725	-0.7089110615787392	0.6875175856887622
0.0360000000000000	0.0460000000000000	1.8540000000000001	-1.2664682767586253	-0.6696801005442448	0.6745847974104981
0.0460000000000000	-0.0540000000000000	1.8540000000000001	-2.0768373189223484	1.3516159057965345	0.6465830434572202
0.0460000000000000	-0.0440000000000000	1.8540000000000001	-1.2256503463394848	1.3715339616664797	0.6639254807964547
0.0460000000000000	-0.0340000000000000	1.8540000000000001	-0.5480430542791122	1.2259156230955572	0.6768514975446511
0.0460000000000000	-0.0240000000000000	1.8540000000000001	-0.0441188249700912	0.9525008146334069	0.6859842524645069
0.0460000000000000	-0.0140000000000000	1.8540000000000001	0.2860634725384427	0.5889255951863570	0.6917554226738947
0.0460000000000000	-0.0040000000000000	1.8540000000000001	0.4424725260211417	0.1727721729990598	0.6944320414400411
0.0460000000000000	0.0060000000000000	1.8540000000000001	0.4250952653557947	-0.2584021996148475	0.6941361329111045
0.0460000000000000	0.0160000000000000	1.8540000000000001	0.2339329282749119	-0.6670466097091081	0.6908542865048398
0.0460000000000000	0.0260000000000000	1.8540000000000001	-0.1309985172786769	-1.0156005363412233	0.6844365881413943
0.0460000000000000	0.0360000000000000	1.8540000000000001	-0.6696634825488845	-1.2664738554210018	0.6745849519488839
0.0460000000000000	0.0460000000000000	1.8540000000000001	-1.3819961370878322	-1.3820147352361989	0.6608316869316060

couet · August 20, 2021, 1:43pm

Your macro gives me this plot, is it what you get also ?

fabstr · August 20, 2021, 1:48pm

Sorry,

I posted the wrong data. This should be right

-0.0540000000000000 -0.0540000000000000	3.1291660091856306
-0.0540000000000000 -0.0440000000000000	2.4357663254813104
-0.0540000000000000 -0.0340000000000000	1.8988370546339484
-0.0540000000000000 -0.0240000000000000	1.4935715663385722
-0.0540000000000000 -0.0140000000000000	1.2123979661311821
-0.0540000000000000 -0.0040000000000000	1.0694401270265372
-0.0540000000000000 0.0060000000000000	1.0857857113167149
-0.0540000000000000 0.0160000000000000	1.2583142407951051
-0.0540000000000000 0.0260000000000000	1.56476774280438
-0.0540000000000000 0.0360000000000000	1.9950949179004138
-0.0540000000000000 0.0460000000000000	2.5609205827938437
-0.0440000000000000 -0.0540000000000000	2.4357650823548265
-0.0440000000000000 -0.0440000000000000	1.8523885232988515
-0.0440000000000000 -0.0340000000000000	1.4227212987846838
-0.0440000000000000 -0.0240000000000000	1.114120694481642
-0.0440000000000000 -0.0140000000000000	0.9085561034473565
-0.0440000000000000 -0.0040000000000000	0.8067705848975394
-0.0440000000000000 0.0060000000000000	0.8183132965968253
-0.0440000000000000 0.0160000000000000	0.9416417012154975
-0.0440000000000000 0.0260000000000000	1.167290603008557
-0.0440000000000000 0.0360000000000000	1.49808724472905
-0.0440000000000000 0.0460000000000000	1.955552141849172
-0.0340000000000000 -0.0540000000000000	1.8988356262117414
-0.0340000000000000 -0.0440000000000000	1.4227211995110418
-0.0340000000000000 -0.0340000000000000	1.1051165602668966
-0.0340000000000000 -0.0240000000000000	0.9022477521024336
-0.0340000000000000 -0.0140000000000000	0.7811560061348227
-0.0340000000000000 -0.0040000000000000	0.725641026220933
-0.0340000000000000 0.0060000000000000	0.7317836189710558
-0.0340000000000000 0.0160000000000000	0.7998454407622148
-0.0340000000000000 0.0260000000000000	0.9354567815145595
-0.0340000000000000 0.0360000000000000	1.1581483284523184
-0.0340000000000000 0.0460000000000000	1.5037879249718333
-0.0240000000000000 -0.0540000000000000	1.493570414704141
-0.0240000000000000 -0.0440000000000000	1.114121029648856
-0.0240000000000000 -0.0340000000000000	0.9022481712306253
-0.0240000000000000 -0.0240000000000000	0.7944575170574648
-0.0240000000000000 -0.0140000000000000	0.7408403222186396
-0.0240000000000000 -0.0040000000000000	0.7181379637618363
-0.0240000000000000 0.0060000000000000	0.7206133078236815
-0.0240000000000000 0.0160000000000000	0.7486945136088412
-0.0240000000000000 0.0260000000000000	0.8104682470827466
-0.0240000000000000 0.0360000000000000	0.9342886845137425
-0.0240000000000000 0.0460000000000000	1.1746454245602445
-0.0140000000000000 -0.0540000000000000	1.2123968793187938
-0.0140000000000000 -0.0440000000000000	0.9085567763847663
-0.0140000000000000 -0.0340000000000000	0.781156749507556
-0.0140000000000000 -0.0240000000000000	0.7408406223138533
-0.0140000000000000 -0.0140000000000000	0.7276345597709936
-0.0140000000000000 -0.0040000000000000	0.7221641200047996
-0.0140000000000000 0.0060000000000000	0.7227930757971472
-0.0140000000000000 0.0160000000000000	0.7294479522619624
-0.0140000000000000 0.0260000000000000	0.7455091560753337
-0.0140000000000000 0.0360000000000000	0.7969341946312738
-0.0140000000000000 0.0460000000000000	0.9524688878502339
-0.0040000000000000 -0.0540000000000000	1.0694381184365775
-0.0040000000000000 -0.0440000000000000	0.8067708483663969
-0.0040000000000000 -0.0340000000000000	0.7256416165719507
-0.0040000000000000 -0.0240000000000000	0.7181382685654851
-0.0040000000000000 -0.0140000000000000	0.7221642156336473
-0.0040000000000000 -0.0040000000000000	0.7234193114202491
-0.0040000000000000 0.0060000000000000	0.7233470171938798
-0.0040000000000000 0.0160000000000000	0.7215278206992729
-0.0040000000000000 0.0260000000000000	0.717628805475584
-0.0040000000000000 0.0360000000000000	0.7328523913715066
-0.0040000000000000 0.0460000000000000	0.8413510822629487
0.0060000000000000 -0.0540000000000000	1.0857813595494574
0.0060000000000000 -0.0440000000000000	0.8183120389346672
0.0060000000000000 -0.0340000000000000	0.7317834695940554
0.0060000000000000 -0.0240000000000000	0.7206133737291783
0.0060000000000000 -0.0140000000000000	0.7227931779679931
0.0060000000000000 -0.0040000000000000	0.7233471089553617
0.0060000000000000 0.0060000000000000	0.723347289201317
0.0060000000000000 0.0160000000000000	0.7224152005114718
0.0060000000000000 0.0260000000000000	0.720670578702164
0.0060000000000000 0.0360000000000000	0.7399788215115453
0.0060000000000000 0.0460000000000000	0.8539948534660476
0.0160000000000000 -0.0540000000000000	1.2583064386978016
0.0160000000000000 -0.0440000000000000	0.941638038346347
0.0160000000000000 -0.0340000000000000	0.799844037908496
0.0160000000000000 -0.0240000000000000	0.7486941613004415
0.0160000000000000 -0.0140000000000000	0.7294480582563068
0.0160000000000000 -0.0040000000000000	0.7215280631881427
0.0160000000000000 0.0060000000000000	0.7224153586403432
0.0160000000000000 0.0160000000000000	0.7321391074169578
0.0160000000000000 0.0260000000000000	0.7551242466166437
0.0160000000000000 0.0360000000000000	0.8183439335377097
0.0160000000000000 0.0460000000000000	0.9884140393990776
0.0260000000000000 -0.0540000000000000	1.5647556672318639
0.0260000000000000 -0.0440000000000000	1.1672838922059983
0.0260000000000000 -0.0340000000000000	0.9354535955391516
0.0260000000000000 -0.0240000000000000	0.8104671816795672
0.0260000000000000 -0.0140000000000000	0.7455091812892316
0.0260000000000000 -0.0040000000000000	0.717629173365207
0.0260000000000000 0.0060000000000000	0.7206707931428092
0.0260000000000000 0.0160000000000000	0.7551241698130918
0.0260000000000000 0.0260000000000000	0.8294977380146555
0.0260000000000000 0.0360000000000000	0.9714211838901601
0.0260000000000000 0.0460000000000000	1.2316928688661168
0.0360000000000000 -0.0540000000000000	1.9950774688509785
0.0360000000000000 -0.0440000000000000	1.4980765963284857
0.0360000000000000 -0.0340000000000000	1.1581425050305691
0.0360000000000000 -0.0240000000000000	0.9342861297259811
0.0360000000000000 -0.0140000000000000	0.7969335392420885
0.0360000000000000 -0.0040000000000000	0.7328523603627136
0.0360000000000000 0.0060000000000000	0.7399784481744887
0.0360000000000000 0.0160000000000000	0.8183429540632309
0.0360000000000000 0.0260000000000000	0.971420135825857
0.0360000000000000 0.0360000000000000	1.2156396876049054
0.0360000000000000 0.0460000000000000	1.5835018099131666
0.0460000000000000 -0.0540000000000000	2.5608960225196875
0.0460000000000000 -0.0440000000000000	1.9555360450621848
0.0460000000000000 -0.0340000000000000	1.503777993595392
0.0460000000000000 -0.0240000000000000	1.174639803183654
0.0460000000000000 -0.0140000000000000	0.9524658690919564
0.0460000000000000 -0.0040000000000000	0.8413489289378872
0.0460000000000000 0.0060000000000000	0.8539921852139443
0.0460000000000000 0.0160000000000000	0.9884105622856332
0.0460000000000000 0.0260000000000000	1.2316892887950373
0.0460000000000000 0.0360000000000000	1.5834993096684047
0.0460000000000000 0.0460000000000000	2.0631472486927693

couet · August 20, 2021, 1:57pm

I simplified your macro:

void Contour_Plot(){
   const Int_t NCont = 50;
   gStyle->SetNumberContours(NCont);
   auto g = new TGraph2D("Test_data.txt","%lg %lg %lg");
   g->SetNpx(200);
   g->SetNpy(200);
   g->SetTitle("Contour plot of the magnetic flux density (T) in the x-y plane");
   g->GetHistogram()->GetXaxis()->SetTitle("x (m)");
   g->GetHistogram()->GetYaxis()->SetTitle("y (m)");
   g->SetLineWidth(1);
   g->SetLineStyle(1);
   g->Draw("colz cont3 ");
}

it gives me this plot:

What’s wrong with it ?

fabstr · August 20, 2021, 2:03pm

Yes, thanks for the help. Is it possible to remove some of the contour lines? I want to see the contour lines in the case when r <= 0.05.

couet · August 20, 2021, 2:04pm

Which value of contour level do you want to see ?

Wile_E_Coyote · August 21, 2021, 6:33pm

{
  const Int_t NRGBs = 5;
  const Int_t NCont = 99;
  Double_t stops[NRGBs] = { 0.00, 0.34, 0.61, 0.84, 1.00 };
  Double_t red[NRGBs]   = { 0.00, 0.00, 0.87, 1.00, 0.51 };
  Double_t green[NRGBs] = { 0.00, 0.81, 1.00, 0.20, 0.00 };
  Double_t blue[NRGBs]  = { 0.51, 1.00, 0.12, 0.00, 0.00 };
  TColor::CreateGradientColorTable(NRGBs, stops, red, green, blue, NCont);
  gStyle->SetNumberContours(NCont);
  //
  TGraph2D *g = new TGraph2D("Test_data.txt", "%lg %lg %lg");
  g->SetNpx(200);
  g->SetNpy(200);
  g->SetTitle("Contour plot of the magnetic flux density (T) in the x-y plane");
  g->GetHistogram()->SetXTitle("         x [m]");
  g->GetHistogram()->GetXaxis()->CenterTitle(kTRUE);
  g->GetHistogram()->GetXaxis()->SetTitleOffset(1.1);
  g->GetHistogram()->GetXaxis()->SetTitleSize(0.032);
  g->GetHistogram()->GetXaxis()->SetLabelSize(0.032);
  g->GetHistogram()->SetYTitle("         y [m]");
  g->GetHistogram()->GetYaxis()->CenterTitle(kTRUE);
  g->GetHistogram()->GetYaxis()->SetTitleOffset(1.3);
  g->GetHistogram()->GetYaxis()->SetTitleSize(0.032);
  g->GetHistogram()->GetYaxis()->SetLabelSize(0.032);
  g->GetHistogram()->GetZaxis()->SetLabelSize(0.032);
  g->Draw("colz");
  gPad->GetCanvas()->SetRealAspectRatio();
  gPad->Modified(); gPad->Update();
  //
  TH2 *h = (TH2*)g->GetHistogram()->Clone();
  h->SetLineColor(kWhite);
  h->SetLineWidth(1);
  h->SetLineStyle(1);
  Double_t dl = 0.05;
  Double_t lmin = dl * Int_t(h->GetMinimum() / dl);
#if 1 /* 0 or 1 */
  Int_t nlevels = 11;
#else /* 0 or 1 */
  Double_t lmax = 1.2;
  if (lmax <= lmin) lmax = lmin + 2 * dl;// just a precaution
  Int_t nlevels = 1 + Int_t((lmax - lmin) / dl + 0.5);
#endif /* 0 or 1 */
  Double_t *levels = new Double_t[nlevels];
  for (int i = 0; i < nlevels; i++) levels[i] = lmin + i * dl;
  h->SetContour(nlevels, levels);
  delete [] levels; // no longer needed
  h->Draw("cont3 same");
#if 1 /* 0 or 1 */
  TEllipse *e = new TEllipse(0., 0., 0.05); e->SetFillStyle(0); e->Draw();
#endif /* 0 or 1 */
  gPad->Modified(); gPad->Update();
}