BFMagnet Class Reference

This class defines magnetic field of an analysis magnet. More...

#include <BFMagnet.h>

List of all members.

Public Types
	kJGG
	kRosie
	kNMagnet
enum	{ kJGG, kRosie, kNMagnet }
Public Member Functions
bool	BatX (const double *pos, double *b) const
	Returns magnetic field in kG at a given point.
bool	BatXrotZ (const double *pos, double *b, double ang) const
	Return field values if field is rotated by angle ang (in rad) about z-axis.
double	Bydl () const
double	ZMin () const
double	ZMax () const
int	NGridX () const
int	NGridY () const
int	NGridZ () const
int	MinGridX () const
int	MinGridY () const
int	MinGridZ () const
double	BfromMap (int x, int y, int z, int crd) const
	Returns the measurement from the map.
void	Init ()
	Reinitializes magnet, i.e.
bool	IsScaled () const
double	ByAtCenter ()
	Returns By at the center of the grid, using the actual measurement point rather than interpolation.
double *	CenterPos ()
void	Scale (double r)
	Scale the entire field map by a factor f.
void	SetByAtCenter (double by)
	Reinitializes B-field map, and scales it to get the right By at the central measurement point.
void	SetCenterPos (const double *pos)
	Shifts the center of the magnet to a given position.
void	SetCenterPos (double x, double y, double z)
	Shifts the center of the magnet to a given position.
void	SetUniformField (const double *b)
	This function sets the grid to a uniform field.
Static Public Member Functions
static BFMagnet &	JGG ()
	Return the reference to JGG magnet.
static BFMagnet &	Rosie ()
	Return the reference to Rosie magnet.
Private Member Functions
	BFMagnet (int mag)
	Constructor.
void	ReadFieldMap ()
Private Attributes
int	fId
	Magnet's id (kJGG or kRosie).
std::string	fMapFileName
int	fNGrid [3]
	Number of points in the grid in x, y, z.
int	fNGridMin [3]
	Point (0, 0, 0) is at the center, minimum is adjusted accordingly.
int	fNGridMax [3]
	Maximum is calculated based on fNGrid and fNGridMin.
double	fGridLen [3]
	Grid spacing, in cm.
double	fOffset [3]
	Magnet center in cm.
double	fZMin
	Minimum z where field is non-zero.
double	fZMax
	Maximum z where field is non-zero.
double ****	fMap
	Array of grid measurements for each coordinate.
double	fMaxB
bool	fIsScaled
double	fBydl
	Calculated Bdl for x=y=0;.
Static Private Attributes
static BFMagnet *	fsMagnet [kNMagnet] = {0, 0}

---

Detailed Description

This class defines magnetic field of an analysis magnet.

The field is assumed to be measured on a 3-D grid with uniformly separated points.

Definition at line 17 of file BFMagnet.h.

---

Member Enumeration Documentation

anonymous enum

Enumerator:

kJGG
kRosie
kNMagnet

Definition at line 19 of file BFMagnet.h.

       {
    kJGG,
    kRosie,
    kNMagnet
  };

---

Constructor & Destructor Documentation

BFMagnet::BFMagnet

(

int

mag

)

[private]

Constructor.

Needs to know which magnet it is.

Definition at line 52 of file BFMagnet.cxx.

References Init().

Referenced by JGG(), and Rosie().

                          :
  fId(mag),
  fMap(0),
  fIsScaled(false)
{
  Init();
}

---

Member Function Documentation

bool BFMagnet::BatX	(	const double *	x,
		double *	b
	)			const

Returns magnetic field in kG at a given point.

Coordinates must be in cm.

Parameters:

	pos	- (x, y, z) point coordinate
	b	- array which will get filled with (Bx, By, Bz)

Returns:

- true if the point is inside the grid, false otherwise. In the latter case, Bx = By = Bz = 0.

Definition at line 239 of file BFMagnet.cxx.

References fGridLen, fMap, fMaxB, fNGrid, fNGridMin, and fOffset.

Referenced by b_xyz(), BatXrotZ(), config_bfield(), and main().

{
  //
  // This is basically copied from rosy_magf.F in e907mc 
  // (which is copied from Donut/E872, which is copied from E771, which ...)
  // A minor improvement is how I deal with the ends of the map to get a smooth
  // transition from the last measured field values to the zero field assumed
  // outside the fieldmap region: I extend the grid by a layer and
  // consider any coordinate within that shell legal, i.e. increment
  // the field region by one grid spacing on all sides.
  //
  // Interpolation in three dimensions:
  // C           --B(1,2,2)-----------B(2,2,2)
  // C            /|                  /|
  // C         | / |                 / |
  // C         |/  |                /  |
  // C       --B(1,1,2)------------B(2,1,2)
  // C        /|   |               |   |
  // C       / |   |       *<------|----------BX,BY,BZ
  // C         |   |               |   |
  // C         |   |               |   |
  // C         |   B(1,2,1)--------|---B(2,2,1)      Z
  // C         |  /                |  /              ^   Y
  // C         | /                 | /               |  /
  // C         |/                  |/                | /
  // C       --B(1,1,1)------------B(2,1,1)          0 ----> X
  //          /|                  /|

  register int i, j, k, crd;

  // Reset field values to 0
  for (crd = 0; crd < 3; ++crd) b[crd] = 0.;

  // It'd be hard to track particles through mG fields...
  if (fMaxB < 1e-5 ) return true; 

  double xLoc[3];
  double gridPos[3]; //
  int gridN[3];   // grid coordinates of data surrounding (x[0],x[1],x[2])
  for (i = 0; i < 3; ++i) {
    xLoc[i] = x[i] - fOffset[i]; // Convert x[] position to grid position
    gridPos[i] = xLoc[i] / fGridLen[i];   // Compute grid coordinates
    gridPos[i] -= fNGridMin[i]; 
    
    if (gridPos[i]  <= 0.0 || gridPos[i] >= (fNGrid[i]-1)) {
      b[0] = b[1] = b[2] = 0.0;
      return false;
    }

    gridN[i] = (int) floor(gridPos[i]);
    gridPos[i] -= gridN[i];
  }

  // For linear interpolation, we can calculate the coefficient
  // for each of the 8 points surrounding the point of interest.
  // These coefficients are (obviously) the same for all 3
  // components of the B-field, so by using one set for all 3
  // components, we should save computational time.
  double xy = gridPos[0] * gridPos[1];
  double xz = gridPos[0] * gridPos[2];
  double yz = gridPos[1] * gridPos[2];
  double xyz = xy * gridPos[2];

  double coef[8] = {
    1 - gridPos[0] - gridPos[1] - gridPos[2] + xy + xz + yz - xyz,
    gridPos[2] - xz - yz + xyz,
    gridPos[1] - xy - yz + xyz,
    yz - xyz,
    gridPos[0] - xy - xz + xyz,
    xz - xyz,
    xy - xyz,
    xyz
  };

  // Loop through the 8 points of interest and add in the contribution
  // from each one to each of the components
  double* coefPtr = coef;
  for (i = gridN[0]; i < gridN[0]+2; ++i) {
    for (j = gridN[1]; j < gridN[1]+2; ++j) {
      for (k = gridN[2]; k < gridN[2]+2; ++k) {
    for (crd = 0; crd < 3; ++crd) {
      b[crd] += (*coefPtr) * fMap[i][j][k][crd]; 
    }
    ++coefPtr;
      }
    }
  }

  return true;
}

bool BFMagnet::BatXrotZ	(	const double *	pos,
		double *	b,
		double	ang
	)			const

Return field values if field is rotated by angle ang (in rad) about z-axis.

This can be used to remove potential bleed of By into Bx

Definition at line 430 of file BFMagnet.cxx.

References BatX().

Referenced by b_xyz_rotz().

{
  if (!BatX(pos, b)) return false;

  double ca = cos(ang);
  double sa = sin(ang);
  double bxp = b[0] * ca + b[1] * sa;
  double byp = -b[0] * sa + b[1] * ca;

  b[0] = bxp;
  b[1] = byp;

  return true;
}

double BFMagnet::BfromMap	(	int	x,
		int	y,
		int	z,
		int	crd
	)			const

Returns the measurement from the map.

Parameters:

	x	- grid position in x
	y	- grid position in y
	z	- grid position in z
	crd	- coordinate (0-2)

Definition at line 370 of file BFMagnet.cxx.

References fMap, and fNGrid.

Referenced by main().

{
  assert(x >= 0 && x < fNGrid[0]);
  assert(y >= 0 && y < fNGrid[1]);
  assert(z >= 0 && z < fNGrid[2]);
  assert(crd >= 0 && crd < 3);
  return fMap[x][y][z][crd];
}

double BFMagnet::ByAtCenter

(

)

Returns By at the center of the grid, using the actual measurement point rather than interpolation.

Definition at line 400 of file BFMagnet.cxx.

References fMap, and fNGridMin.

Referenced by AlignChamW0::AdjustBField(), TrackBeamPart::EndRun(), AlignChamW0::EndRun(), SPTrkBuilder::FitTPCTracks(), SetByAtCenter(), KalmanRefit::SetupManager(), KalmanReco::SetupManager(), and TheEnd().

{
  int i0 = -fNGridMin[0];
  int i1 = -fNGridMin[1];
  int i2 = -fNGridMin[2];
  return fMap[i0][i1][i2][1];
}

double BFMagnet::Bydl

(

)

const [inline]

Definition at line 31 of file BFMagnet.h.

References fBydl.

{return fBydl;}

double* BFMagnet::CenterPos

(

)

[inline]

Definition at line 50 of file BFMagnet.h.

References fOffset.

Referenced by AlignChamZ::EndRun(), TrkCandBuilder::MakeTrack(), and TPCRHitFind::NewRun().

{return fOffset;}

void BFMagnet::Init

(

)

Reinitializes magnet, i.e.

reads the field map again

Definition at line 64 of file BFMagnet.cxx.

References fBydl, fGridLen, fId, fMap, fMapFileName, fNGrid, fNGridMin, kJGG, kRosie, ReadFieldMap(), and SetCenterPos().

Referenced by BFMagnet(), and config_bfield().

{
  // Assume that the field data file lives in $SRT_PUBLIC_CONTEXT/Bfield
  fMapFileName = getenv("SRT_PRIVATE_CONTEXT");
  fMapFileName += "/Bfield/Maps/";
  switch (fId) {
  case kJGG:
    fMapFileName += "JGGfield.dat";
    break;

  case kRosie:
    fMapFileName += "Rosiefield.dat";
    break;

  default:
    abort();
  }

  struct stat buf;
  if (stat(fMapFileName.c_str(), &buf) != 0) {
    fMapFileName = getenv("SRT_PUBLIC_CONTEXT");
    fMapFileName += "/Bfield/Maps/";
    switch (fId) {
    case kJGG:
      fMapFileName += "JGGfield.dat";
      break;
      
    case kRosie:
      fMapFileName += "Rosiefield.dat";
      break;
      
    default:
      abort();
    }
    if (stat(fMapFileName.c_str(), &buf) != 0) {
      cout << "Couldn't find " << fMapFileName << endl;
      exit(-1);
    }
  }

  cout << "Loading field map from " << fMapFileName << endl;
  ReadFieldMap();

  SetCenterPos(0, 0, 0);

  // Calculate Bydl
  fBydl = 0;
  
  int ix = -fNGridMin[0];
  int iy = -fNGridMin[1];
  for (int i = 1; i < fNGrid[2] - 1; ++i) {
    fBydl += fGridLen[2] * fMap[ix][iy][i][1];
  }
  cout << "Bydl = " << fBydl << " kG*cm" << endl;
}

bool BFMagnet::IsScaled

(

)

const [inline]

Definition at line 47 of file BFMagnet.h.

References fIsScaled.

Referenced by config_bfield().

{ return fIsScaled; }

BFMagnet & BFMagnet::JGG

(

)

[static]

Return the reference to JGG magnet.

Definition at line 30 of file BFMagnet.cxx.

References BFMagnet(), fsMagnet, and kJGG.

Referenced by AlignChamW0::AdjustBField(), b_xyz(), b_xyz_rotz(), config_bfield(), TrackBeamPart::EndRun(), AlignChamZ::EndRun(), AlignChamW0::EndRun(), SPTrk::Fit(), SPTrkBuilder::FitTPCTracks(), gsFCN(), InitZslices(), main(), TPCRHitFind::NewRun(), AlignChamW0::NewRun(), KalmanRefit::SetupManager(), KalmanReco::SetupManager(), and TheEnd().

{
  
  if (!fsMagnet[kJGG]) fsMagnet[kJGG] = new BFMagnet(kJGG);
  return *fsMagnet[kJGG];
}

int BFMagnet::MinGridX

(

)

const [inline]

Definition at line 40 of file BFMagnet.h.

References fNGridMin.

Referenced by main().

{return fNGridMin[0];}

int BFMagnet::MinGridY

(

)

const [inline]

Definition at line 41 of file BFMagnet.h.

References fNGridMin.

Referenced by main().

{return fNGridMin[1];}

int BFMagnet::MinGridZ

(

)

const [inline]

Definition at line 42 of file BFMagnet.h.

References fNGridMin.

Referenced by main().

{return fNGridMin[2];}

int BFMagnet::NGridX

(

)

const [inline]

Definition at line 36 of file BFMagnet.h.

References fNGrid.

Referenced by main().

{return fNGrid[0];}

int BFMagnet::NGridY

(

)

const [inline]

Definition at line 37 of file BFMagnet.h.

References fNGrid.

Referenced by main().

{return fNGrid[1];}

int BFMagnet::NGridZ

(

)

const [inline]

Definition at line 38 of file BFMagnet.h.

References fNGrid.

Referenced by main().

{return fNGrid[2];}

void BFMagnet::ReadFieldMap

(

)

[private]

Definition at line 122 of file BFMagnet.cxx.

References fGridLen, fMap, fMapFileName, fMaxB, fNGrid, fNGridMax, fNGridMin, and getline().

Referenced by Init(), and SetByAtCenter().

{
  std::ifstream fin(fMapFileName.c_str());
  if (!fin) {
    cout << "The file " << fMapFileName << " could not be opened. \n"
     << "Magnetic field not read!" << endl;
    exit(-1);
  }

  string tmpStr;
  // Discard two comment lines (mandatory)
  getline(fin,tmpStr); 
  getline(fin,tmpStr);

  // Read grid size -- 3 numbers
  for (int i = 0; i < 3; ++i) fin >> fNGrid[i];

  // Read grid min point position, and initialize max point
  for (int i = 0; i < 3; ++i) {
    fin >> fNGridMin[i];
    fNGridMin[i]--;
    fNGrid[i] += 2;
    fNGridMax[i] = fNGridMin[i]  + fNGrid[i] - 1;
  }

  // Read grid cell spacing
  for (int i = 0; i < 3; ++i) {
    fin >> fGridLen[i];
    fGridLen[i] /= 10.0;  //convert mm to cm
  }

  double tmpVal;
  fin >> tmpVal;
  getline(fin, tmpStr); // Ignore line with nominal field
  getline(fin, tmpStr); // Ignore comment line 

  // Allocate memory for arrays to hold grid points
  bool reMakeMap = false;
  if (!fMap) {
    fMap = new double***[fNGrid[0]];
    reMakeMap = true;
  }

  // Now loop through all grid points, allocate memory
  // and read in field value
  fMaxB = 0;
  for (int i = 0; i < fNGrid[0]; ++i) {
    if (reMakeMap) fMap[i] = new double**[fNGrid[1]];
    for (int j = 0; j < fNGrid[1]; ++j) {
      if (reMakeMap) fMap[i][j] = new double*[fNGrid[2]];
      for (int k = 0; k < fNGrid[2]; ++k) {
    if (reMakeMap) fMap[i][j][k] = new double[3];
    for (int crd = 0; crd < 3; ++crd) {
      if ((i == 0) || i == (fNGrid[0] - 1) ||
          (j == 0) || j == (fNGrid[1] - 1) ||
          (k == 0) || k == (fNGrid[2] - 1)) {
        fMap[i][j][k][crd] = 0.0;
        continue;
      }

      if (!(fin >> tmpVal)) {
        cout << "Couldn't read values at (" 
         << i << ", " << j << ", " << k << ", " << crd 
         << ") from " << fMapFileName << endl;
        exit(-1);
      }
      tmpVal *= 10.0;  // Convert from T to kG
      if (fabs(tmpVal) > fMaxB) fMaxB = fabs(tmpVal);
      fMap[i][j][k][crd] = tmpVal;
    }
      }
    }
  }

  getline(fin, tmpStr);
  getline(fin, tmpStr);
  assert(tmpStr.find(" all done...") != string::npos);
  fin.close();
}

BFMagnet & BFMagnet::Rosie

(

)

[static]

Return the reference to Rosie magnet.

Definition at line 41 of file BFMagnet.cxx.

References BFMagnet(), fsMagnet, and kRosie.

Referenced by b_xyz(), b_xyz_rotz(), config_bfield(), AlignChamZ::EndRun(), gsFCN(), InitZslices(), main(), TrkCandBuilder::MakeTrack(), AlignChamW0::NewRun(), RosieFCN(), SPTrack::ROSYBdL(), and TheEnd().

{
  
  if (!fsMagnet[kRosie]) fsMagnet[kRosie] = new BFMagnet(kRosie);
  return *fsMagnet[kRosie];
}

void BFMagnet::Scale

(

double

r

)

Scale the entire field map by a factor f.

Definition at line 334 of file BFMagnet.cxx.

References fBydl, fGridLen, fIsScaled, fMap, fMaxB, fNGrid, and fNGridMin.

Referenced by config_bfield(), main(), TPCRHitFind::NewRun(), and SetByAtCenter().

{  
  fIsScaled = true;
  fMaxB = 0;

  for (int i = 1; i < fNGrid[0] - 1; ++i) {
    for (int j = 1; j < fNGrid[1] - 1; ++j) {
      for (int k = 1; k < fNGrid[2] - 1; ++k) {
    for (int crd = 0; crd < 3; ++crd) {
      fMap[i][j][k][crd] *= f;
      if (fabs(fMap[i][j][k][crd]) > fMaxB) {
        fMaxB = fabs(fMap[i][j][k][crd]);
      }
    }
      }
    }
  }
  // Calculate Bydl
  fBydl = 0;
  
  int ix = -fNGridMin[0];
  int iy = -fNGridMin[1];
  for (int i = 1; i < fNGrid[2] - 1; ++i) {
    fBydl += fGridLen[2] * fMap[ix][iy][i][1];
  }
  cout << "Bydl = " << fBydl << " kG*cm" << endl;
}

void BFMagnet::SetByAtCenter

(

double

by

)

Reinitializes B-field map, and scales it to get the right By at the central measurement point.

The reason for re-initializing the map is to avoid round-off errors, as this procedure will be used in fitting

Definition at line 414 of file BFMagnet.cxx.

References ByAtCenter(), ReadFieldMap(), and Scale().

Referenced by AlignChamW0::AdjustBField(), and gsFCN().

{
  //ReadFieldMap();
  double byNow = ByAtCenter();
  if (fabs(byNow) < 0.1) {
    ReadFieldMap();
    byNow = ByAtCenter();
  }
  if (fabs((by - byNow) / byNow) > 1e-8) Scale(by / byNow);
}

void BFMagnet::SetCenterPos	(	double	x,
		double	y,
		double	z
	)

Shifts the center of the magnet to a given position.

Parameters:

x,y,z,:

(x, y, z) coordinates of the magnet center

Definition at line 221 of file BFMagnet.cxx.

References fGridLen, fNGridMax, fNGridMin, fOffset, fZMax, and fZMin.

{
  fOffset[0] = x;
  fOffset[1] = y;
  fOffset[2] = z;
  fZMin = fOffset[2] + ((double) fNGridMin[2]) * fGridLen[2];
  fZMax = fOffset[2] + ((double) fNGridMax[2]) * fGridLen[2];
}

void BFMagnet::SetCenterPos

(

const double *

pos

)

Shifts the center of the magnet to a given position.

Parameters:

pos

- array of 3 doubles containing (x, y, z) of the magnet center

Definition at line 208 of file BFMagnet.cxx.

References fGridLen, fNGridMax, fNGridMin, fOffset, fZMax, and fZMin.

Referenced by config_bfield(), gsFCN(), Init(), TPCRHitFind::NewRun(), and RosieFCN().

{
  for (int i = 0; i < 3; ++i) {
    fOffset[i] = pos[i];
  }
  fZMin = fOffset[2] + ((double) fNGridMin[2]) * fGridLen[2];
  fZMax = fOffset[2] + ((double) fNGridMax[2]) * fGridLen[2];
}

void BFMagnet::SetUniformField

(

const double *

b

)

This function sets the grid to a uniform field.

The feature may be useful for testing.

Parameters:

b

- 3 components of the field in the region of the grid in kG

Definition at line 384 of file BFMagnet.cxx.

References fMap, and fNGrid.

Referenced by main().

{
  for (int i = 0; i < fNGrid[0]; ++i) {
    for (int j = 0 ; j < fNGrid[1]; ++j) {
      for (int k = 0; k < fNGrid[2]; ++k) {
    for (int crd = 0; crd < 3; ++crd) {
      fMap[i][j][k][crd] = b[crd];
    }
      }
    }
  }
}

double BFMagnet::ZMax

(

)

const [inline]

Definition at line 34 of file BFMagnet.h.

References fZMax.

Referenced by config_bfield(), InitZslices(), main(), and SPTrack::ROSYBdL().

{return fZMax;}

double BFMagnet::ZMin

(

)

const [inline]

Definition at line 33 of file BFMagnet.h.

References fZMin.

Referenced by config_bfield(), InitZslices(), main(), and SPTrack::ROSYBdL().

{return fZMin;}

---

Member Data Documentation

double BFMagnet::fBydl [private]

Calculated Bdl for x=y=0;.

Definition at line 85 of file BFMagnet.h.

Referenced by Bydl(), Init(), and Scale().

double BFMagnet::fGridLen[3] [private]

Grid spacing, in cm.

Definition at line 75 of file BFMagnet.h.

Referenced by BatX(), Init(), ReadFieldMap(), Scale(), and SetCenterPos().

int BFMagnet::fId [private]

Magnet's id (kJGG or kRosie).

Definition at line 67 of file BFMagnet.h.

Referenced by Init().

bool BFMagnet::fIsScaled [private]

Definition at line 83 of file BFMagnet.h.

Referenced by IsScaled(), and Scale().

double**** BFMagnet::fMap [private]

Array of grid measurements for each coordinate.

Definition at line 81 of file BFMagnet.h.

Referenced by BatX(), BfromMap(), ByAtCenter(), Init(), ReadFieldMap(), Scale(), and SetUniformField().

std::string BFMagnet::fMapFileName [private]

Definition at line 68 of file BFMagnet.h.

Referenced by Init(), and ReadFieldMap().

double BFMagnet::fMaxB [private]

Definition at line 82 of file BFMagnet.h.

Referenced by BatX(), ReadFieldMap(), and Scale().

int BFMagnet::fNGrid[3] [private]

Number of points in the grid in x, y, z.

Definition at line 70 of file BFMagnet.h.

Referenced by BatX(), BfromMap(), Init(), NGridX(), NGridY(), NGridZ(), ReadFieldMap(), Scale(), and SetUniformField().

int BFMagnet::fNGridMax[3] [private]

Maximum is calculated based on fNGrid and fNGridMin.

Definition at line 73 of file BFMagnet.h.

Referenced by ReadFieldMap(), and SetCenterPos().

int BFMagnet::fNGridMin[3] [private]

Point (0, 0, 0) is at the center, minimum is adjusted accordingly.

Definition at line 72 of file BFMagnet.h.

Referenced by BatX(), ByAtCenter(), Init(), MinGridX(), MinGridY(), MinGridZ(), ReadFieldMap(), Scale(), and SetCenterPos().

double BFMagnet::fOffset[3] [private]

Magnet center in cm.

Definition at line 76 of file BFMagnet.h.

Referenced by BatX(), CenterPos(), and SetCenterPos().

BFMagnet * BFMagnet::fsMagnet = {0, 0} [static, private]

Definition at line 65 of file BFMagnet.h.

Referenced by JGG(), and Rosie().

double BFMagnet::fZMax [private]

Maximum z where field is non-zero.

Definition at line 79 of file BFMagnet.h.

Referenced by SetCenterPos(), and ZMax().

double BFMagnet::fZMin [private]

Minimum z where field is non-zero.

Definition at line 78 of file BFMagnet.h.

Referenced by SetCenterPos(), and ZMin().

---

The documentation for this class was generated from the following files:

• BFMagnet.h
• BFMagnet.cxx

---