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hkl.w
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\subsection{Crystallographic Computations}
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The HKL object performs standard four circle calculations. I.e., given a UB
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matrix it calculates the four circle diffractometer setting angles required
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for a reflection with index hkl. The UB must be determined from a set of
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reflections found manually or automatically. This is done in an offline
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program. The code in this module is a direct reimplementation of fortran code
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provided by Jean Allibon, ILL with the MAD four circle diffractometer
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control program in ANSI-C. For theory, see the contribution by
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W.C. Hamilton in the International Tables for Crystallography, 1974 edition.
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The object uses the following object data structure:
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@d hkldat @{
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typedef struct __HKL {
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pObjectDescriptor pDes;
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double fUB[9];
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double fLambda;
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int iManual;
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double fLastHKL[5];
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int iNOR;
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int iQuad;
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pMotor pTheta;
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pMotor pOmega;
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pMotor pChi;
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pMotor pPhi;
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pMotor pNu;
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pSelVar pMono;
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long lID;
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} HKL;
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@}
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The fields are more or less self explaining:
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\begin{description}
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\item[pDes] The standard object descriptor.
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\item[fUB] The UB matrix.
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\item[iUB] is a flag which spcifies if a UB is specified.
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\item[fLambda] The wavelength of the neutrons.
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\item[iManual] A flag which defines if the wavelength has been set manually
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or is updated automatically from a wavelength variable.
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\item[fLastHKL] the HKL of the last reflection calculated.
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\item[iNor] a flag for normal beam calculation mode.
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\item[pTheta] The two theta motor. All motor are needed for boundary
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checking.
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\item[pOmega] The omega axis motor.
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\item[pChi] The chi axis motor.
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\item[pPhi] the phi axis motor.
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\item[pNu] the nu axis motor for normal beam geometry.
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This is detector tilt.
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\item[pMono] The selector variable doing the wavelength.
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\end{description}
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The wavelength is a bit tricky. As it would be to time consuming to read two
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motors each time a calculation is performed, the lambda variable is updated
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by registering a callback with the selector variable handling the
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monochromator wavelength. As TriCS will be run with two monochromators on a
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lift a means has to be provided to change the selector variable online. An
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additonal feature is that the wavelength can be manipulated manually. This
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adresses the issue that automatic wavelength may be inaccurate due to
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lazy instrument scientists not adjusting their instruments.
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In terms of an interface the following functions will be provided by this
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module:
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@d hklint @{
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typedef struct __HKL *pHKL;
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/*-------------------------------------------------------------------------*/
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pHKL CreateHKL(pMotor pTheta, pMotor pOmega,
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pMotor pChi, pMotor pPhi, pMotor pNu);
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void DeleteHKL(void *pData);
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int HKLFactory(SConnection *pCon, SicsInterp *pSics, void *pData,
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int argc, char *argv[]);
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/*------------------------------------------------------------------------*/
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int SetWavelengthVariable(SConnection *pCon, pHKL self, pSelVar pVar);
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int SetWavelengthManual(pHKL self, float fVal);
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int SetUB(pHKL self, float fUB[9]);
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int GetUB(pHKL self, float fUB[9]);
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int SetNOR(pHKL self, int iNOB);
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int GetLambda(pHKL self, float *fVal);
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int GetCurrentHKL(pHKL self, float fVal[3]);
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int GetCurrentPosition(pHKL self, SConnection *pCon, float fPosition[4]);
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int CalculateSettings(pHKL self, float fHKL[3], float fPsi, int iHamil,
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float fSet[4],SConnection *pCon);
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int RunHKL(pHKL self, float fHKL[3], float fPsi, int iHamil, SConnection
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*pCon);
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int DriveHKL(pHKL self, float fHKL[3], float fPsi, int iHamil,
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SConnection *pCon);
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int DriveSettings(pHKL self, float fSet[4],SConnection *pCon);
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int HKLAction(SConnection *pCon, SicsInterp *pSics, void *pData,
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int argc, char *argv[]);
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@}
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All functions return 0 on failure, 1 on success if not stated otherwise.
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Most functions take a pointer to a HKL data structure as first parameter.
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The function in more detail:
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\begin{description}
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\item[CreateHKL] creates a HKL object. The parameters are pointers to the
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four four circle motors. Returns NULL on failure, a pointer to the new
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object on success.
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\item[DeleteHKL] properly removes an HKL object from the system.
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\item[HKLFactory] The factory function which initialises an HKL object from
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the initialisation script.
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\item[SetWavelengthVariable] sets a new wavelength variable. Installs all
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necesarry callbacks for automatic update.
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\item[SetWaveLengthManual] deinstall all callbacks and forces the wavelength
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to the value specified a second parameter.
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\item[SetUB] sets the UB matrix.
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\item[SetNOR] sets the normal beam calculation flag to iNOR.
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\item[CalculateSettings] is the heart of this all. As the name suggests
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calculates the settings for a four circle diffractometer. The parameters
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are:
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\begin{description}
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\item[self] A pointer to a HKL data structure.
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\item[fHKL] The reflection indices to calculate the settings for.
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\item[fPsi] The psi value for the reflection. For psi scans. Set to 0 if not
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used.
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\item[iHamil] The index of the hamilton position to calculate. Can be an
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integer between 0 to 8. 0 denotes the normal case.
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\item[fSet] contains the required settings if the function returns with
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success. 0 = two theta, 1 = omega, 2 = chi, 3 = phi.
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\end{description}
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The function returns 1 on success, a negative value on failure. Possible
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error returns are:
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\begin{description}
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\item[HKLIMPOSSIBLE] the calculation was impossible.
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\item[HKLTHETALIMIT] a setting could be calculated but can not be accessed
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due to a limit on two theta.
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\end{description}
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\item[DriveHKL] calculates a setting and drives to the position. The
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parameters are the same as with CalculateSettings. With the addition of a
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pointer to the connection object doing the command for error messages and
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everything. The error returns are the same as with CalculateSettings
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well. With the addition of HKJMOTFAIL, which means that a motor failed to
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drive properly.
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\item[DriveSettings] drives to the the settings given in fSet.
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\item[HKLAction] is the interpreter wrapper function for the HKL object.
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\end{description}
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@o hkl.i @{
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/*-------------------------------------------------------------------------
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H K L
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Internal data structure description. See hkl.h, c,w for more details.
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Mark Koennecke, February 1998
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----------------------------------------------------------------------------*/
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@<hkldat@>
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@}
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@o hkl.h @{
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/*---------------------------------------------------------------------------
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H K L
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This SICS object performs angle setting calculations for a four circle
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diffractometer. The heart of this code is a C transcriptions of routines
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written by Jean Allibon at ILL for the MAD program. Theory is explained in
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the article by W. C. Hamilton in International Tables for Crystallography,
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1974 edition.
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copyright: see copyright.h
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Mark Koennecke, February 1998
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----------------------------------------------------------------------------*/
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#ifndef SICSHKL
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#define SICSHKL
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#include "selector.h"
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#include "selvar.h"
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@<hklint@>
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#endif
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@}
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