000000016089000000858 000000051 000000857 0 Model000001469 000000092 000000092 1 Esoteric000003165 000000137 000000137 1 Adding_terms000003392 000000184 000000184 1 Removing_terms000003530 000000224 000000224 1 Setting000003774 000000264 000000264 1 Fitting000004010 000000306 000000306 1 Inquiring000004267 000000359 000000359 1 Saving_and_restoring000004571 000000437 000000397 1 Terms000014793 000000771 000000857 1 Subsets000004999 000000480 000000480 2 Equatorial000005883 000000523 000000523 2 Altazimuth000006976 000000563 000000563 2 General000007087 000000603 000000603 2 Special000008335 000000647 000000647 2 Polynomials000010151 000000689 000000689 2 Harmonics000011875 000000733 000000733 2 Auxiliaries000013083 000000810 000000397 2 Local000015422 000000857 000000857 2 Syntax000013483 000000397 000000397 3 Implementation0 ModelThe pointing model is a sequence of terms selected from aninternal repertoire. As well as terms that implement specificmechanical effects such as zero points, misaligments andflexures, there are empirical terms such as polynomials andharmonics. The terms fall into five categories: equatorial,altazimuth, general, special and generic. The model for anyparticular telescope may be a mixture of several of thesetypes. For example, equatorially mounted telescopes willtypically require both equatorial terms (e.g. hour angleand declination zero points) and general terms (e.g. tubeflexure).1 EsotericThe model can either start with raw telescope positions andpredict the corresponding "true" position, or alternatively canstart with "true" star positions and predict the required rawtelescope position. This option is chosen with the ADJUSTcommand. The sign convention for the coefficients is thesame for both options, so that the two options should delivercoefficients that are substantially the same. When the ADJUSTcommand is used to change the option, the order of the terms inthe model is reversed so that more or less the same coefficientvalues will be produced (as long as none of the coefficientsis too large). Normally, each term in the model is "chained" to the previousone, the input position for each term being the output positionfrom the previous term. Sometimes this may not be appropriate,and a set of terms can instead share one input position andtheir adjustments be added in as a group; in this case theterms are said to be "parallel". The commands CHAIN and PARALselect which option applies to a given term. Normally the coefficients will not be much altered by changingthe order of terms, or switching terms between chained andparallel. Significant changes are likely only if somecoefficients are large, or if high powered polynomials or highfrequency harmonics are employed. It is nevertheless advisableto ensure that the model being fitted matches the way thepointing corrections are implemented in the telescope controlsystem itself, in direction, order, formulation, and chaining. In the case of "generalized gimbal" mounts, the corrections in"azimuth" and "elevation" are, in fact, in the correspondingmount coordinates1 Adding_termsTerms can be added to the model by means of the USE command. For example, to add the terms for polar axis misalignment: USE ME MA The USE command is also used to re-enable fitting after aFIX command.1 Removing_termsTerms can be removed from the model by means of the LOSEcommand. For example, to drop the term PDH2: LOSE PDH21 SettingThe value of the coefficient of a single term can be changed bymeans of the command: coeff val where coeff is the name of the term and val the value inarcseconds. Thus to set the HA index error to +20 arcsec: IH 201 FittingThe current model is fitted to the observations by means ofthe FIT command. Individual terms can be frozen at aparticular value by means of the FIX command, or includedonce more in the fitting by means of the USE command.1 InquiringThe current value of the coefficient of a single term canbe inquired by entering a command consisting simply of thename of the term. For example, to display the current value of the declinationindex error, simply use the command: ID1 Saving_and_restoringThe current model can be written to a file by means of theOUTMOD command. Such a file can subsequently be read bythe INMOD command. The file format is suitable for readingby programs outside the TPOINT system - for keeping arecord of changes in the coefficients for example.1 TermsThe pointing terms fall into five categories - equatorial,altazimuth, special (to a telescope or type of telescope),polynomial and harmonic. The model for any particulartelescope may be a mixture of several of these types. Some terms are functionally identical but have different namesfor historical or convenience reasons. To find out what a giventerm means in a geometrical sense, refer to the TPOINT manual.2 Equatorial IH index error in HA ID index error in Dec NP nonperpendicularity of HA and Dec axes CH nonperpendicularity of Dec and pointing axes ME polar axis elevation error MA polar axis error EW FO fork flexure DAB Dec axis bending DAF Dec axis flop HCES HA centering error (sin component) HCEC HA centering error (cos component) DCES Dec centering error (sin component) DCEC Dec centering error (cos component) DNP dynamic nonperpendicularity X2HC cos(2H) term EW AUX1H HA change supplied through auxiliary reading 1 AUX1X EW change supplied through auxiliary reading 1 AUX1D Dec change supplied through auxiliary reading 1 AUX2H HA change supplied through auxiliary reading 2 AUX2X EW change supplied through auxiliary reading 2 AUX2D Dec change supplied through auxiliary reading 22 Altazimuth IE index error in elevation IA index error in azimuth CA nonperpendicularity of elevation and pointing axes AN NS misalignment of azimuth axis AW EW misalignment of azimuth axis NPAE nonperpendicularity of azimuth and elevation axes NRX Nasmyth rotator displacement (vertical) NRY Nasmyth rotator displacement (horizontal) CRX altazimuth coude displacement (NS) CRY altazimuth coude displacement (EW) ACES Az centering error (sin component) ACEC Az centering error (cos component) ECES El centering error (sin component) ECEC El centering error (cos component) AUX1A Az change supplied through auxiliary reading 1 AUX1X LR change supplied through auxiliary reading 1 AUX1E El change supplied through auxiliary reading 1 AUX2A Az change supplied through auxiliary reading 2 AUX2X LR change supplied through auxiliary reading 2 AUX2E El change supplied through auxiliary reading 2 In the case where the mounting is a generalized gimbal, thecorrections are with respect to mount coordinates.2 General TF tube flexure - sin Z law TX tube flexure - tan Z law FLOP constant vertical error2 SpecialSpecial-to-telescope: ZH AAT HA Z-gear effect in HA ZE AAT HA Z-gear effect in polar axis elevation HF AAT main east-west horseshoe flexure HGES 36-min gear error in HA - sin HGEC 36-min gear error in HA - cos DGES 9-deg gear error in Dec - sin DGEC 9-deg gear error in Dec - cos TFP AAT tube flexure - non-Hooke's-law term HFX AAT residual horseshoe flexure east-west HFD AAT residual horseshoe flexure north-south CD4A AAT coude 4 collimation error A component CD4B AAT coude 4 collimation error B component CD5A AAT coude 5 collimation error A component CD5B AAT coude 5 collimation error B component AWGS Gemini South azimuth axis tilt Approximate: ANL simple AN dAz,dEl formulas AWL simple AW dAz,dEl formulas CAL simple CA dAz formula CHL simple CH dHA formula MAL simple MA dHA,dDec formulas MEL simple ME dHA,dDec formulas NPL simple NP dHA formula NPAEL simple NPAE dAz formula TXL simple TX dEl formula For off-axis pointing origin (n.b. requires instrument rotatorangle to be supplied in degrees as auxiliary reading #1): POX x-coordinate of pointing origin POY y-coordinate of pointing origin2 Polynomials"Polynomial" terms apply adjustments to a "result" coordinate whichare proportional to the product of two "input" coordinates, eachraised to an integer power greater than or equal to zero. Polynomial terms have names which conform to the following syntax: Prc[i[c[i]]] where: P = the character P r = a single-letter code specifying the "result" coordinate: H result is in hour angle X result is East-West on the sky D result is in declination U result moves polar axis up/down L result moves polar axis left/right P result changes HA/Dec nonperpendicularity A result is in azimuth S result is left-right on the sky Z result is in zenith distance (sky) E result is in elevation (mount) N result moves azimuth axis north/south W result moves azimuth axis east/west V result changes Az/El nonperpendicularity c = a single-letter code specifying an "input" coordinate: H hour angle D declination A azimuth Z zenith distance E elevation Q parallactic angle i = a decimal digit 0-9 A missing i or ci defaults to unity. Examples of valid polynomial term names: PDH = HA adjustment to Dec PZZ2 = ZD**2 adjustment to ZD PXH3D2 = (HA**3)*(Dec**2) adjustment east-west In the case where the mounting is a generalized gimbal, correctionsto A, S and E are with respect to mount coordinates. Corrections toZ always refer to the vertical.2 Harmonics"Harmonic" terms apply adjustments to a "result" coordinate whichare proportional to the product of sines or cosines of two "input"coordinates. Harmonic terms have names which conform to the following syntax: Hrfc[i][fc[i]] or Hrfci[i[i]] where: H = the character H r = a single-letter code specifying the "result" coordinate: H result is in hour angle X result is East-West on the sky D result is in declination U result moves polar axis up/down L result moves polar axis left/right P result changes HA/Dec nonperpendicularity A result is in azimuth S result is left-right on the sky Z result is in zenith distance (sky) E result is in elevation (mount) N result moves azimuth axis north/south W result moves azimuth axis east/west V result changes Az/El nonperpendicularity f = function: 'S' for sine or 'C' for cosine c = a single-letter code specifying an "input" coordinate: H hour angle D declination A azimuth Z zenith distance E elevation Q parallactic angle i = a decimal digit 0-9 A missing i or fci defaults to unity. Examples of valid harmonic term names: HHSH = sin(HA) adjustment to HA HACA12 = cos(12*AZ) adjustment to Az HZSA3 = sin(3*AZ) adjustment to ZD HDSH2CD7 = sin(2*HA)*cos(7*Dec) adjustment to Dec2 Auxiliaries"Auxiliary" terms apply adjustments to a "result" coordinate which areproportional to an auxiliary reading. Auxiliary terms have names which conform to the following syntax: Anr where: A = the character A n = a decimal digit 1-3 r = a single-letter code specifying the "result" coordinate: H result is in hour angle X result is East-West on the sky D result is in declination U result moves polar axis up/down L result moves polar axis left/right P result changes HA/Dec nonperpendicularity A result is in azimuth S result is left-right on the sky Z result is in zenith distance (sky) E result is in elevation (mount) N result moves azimuth axis north/south W result moves azimuth axis east/west V result changes Az/El nonperpendicularity Examples of valid auxiliary term names: A2H = HA adjustment proportional to auxiliary reading #2 A1Z = ZD adjustment proportional to auxiliary reading #12 LocalWhere it is found that the existing library of pointing terms isnot enough to eliminate some observed or predicted systematiceffect, new pointing terms can be added to the system. For detailsof how to add such terms, please select the subtopic"Implementation". For help on any local terms in the version ofTPOINT you are running, please select the top-level topic"Local_Enhancements".3 ImplementationAdding a new term to TPOINT's repertoire involves making theappropriate changes to the tptPterml and tptTrmloc sourcemodules (see below), and then compiling each of them andupdating the object library. Finally, the TPOINT program hasto be relinked. In addition, it is recommended that the helpsource file LOCAL.HLP is edited and translated into the helplibrary LOCAL.SHL by means of the (freestanding) CREHLP utility. Changes to tptPterml: 1) Each additional term requires a further destination to be included in the large switch statement near the start of the module. 2) Insert a case statement with the label chosen in (1) at the appropriate place, followed by the expressions which calculate the pointing change per unit coefficient. Use existing terms as a guide. Make sure the comments are complete and accurate, following the layouts in the tptPterms module. Changes to tptTrmloc: 1) Update the value given in the NCOEFF definition. 2) Add the name of the new coefficient to the coname initialization statement. The tptTrmstd routine can be used as a guide. Other initialization functions required to support a locally- implemented version of tptPterml may also be performed within tptTrmloc.1 SubsetsIt is possible to limit a pointing model term to a specificdata subset. This is done by appending "/subset" to the termname, where "subset" is the name of the data subset, asspecified in the file of observations that is read in usingthe INDAT command. (Subset names are not case-sensitive.) The model may contain multiple instances of the same pointingterm, each instance applying to a different subset. For examplethe two terms ID and ID/A will apply declination zero pointcorrections to all observations (ID) with an additional increment(ID/A) applying only to observations that belong to data subset A.2 SyntaxIn the arguments of USE, LOSE, FIX, CHAIN and PARAL commands,subsetting is indicated as follows: term term that applies to all observations term/= term that applies to the latest subset term/subset term that applies to specified subset term/* all current terms of specified name * all current terms of whatever subset */= all current terms of latest subset */subset all current terms of specified subset The "latest subset" is that of the previous term. It isinitially the empty string and becomes empty again if a globalterm is specified. Otherwise it is the last subset to bespecified.