Differences between revisions 2 and 9 (spanning 7 versions)

Relation between coordinates parameters of the 30m telescope

SL, 06/2013.

Important preliminary remark: for now this page is a sand box where I gather various informations about coordinates variables generated by the 30m telescope control system, which may be useful for the implementation of a new instrument into the system

I gathered these information from various documents, Wiki pages, and email exchanges with specialists of the 30m telescope. Ideally I would like that this page contains the list of the various coordinates values delivered by the telescope, with their descriptions and the relations between them. It would good also to centralizes here links to related documents and wiki pages.

Table of the coordinates parameters generated by the New Control System of the 30m telescope

In particular I list the variables from the antMD.trace category, that are also broadcast on the local network by the Elvin server. The correspondence with the parameters in the IMBFITS files recorded at the end of each scan, and the time stamp information and possibly units of these parameters are also displayed.

antMD.trace. parameter name	IMBFITS parameter name	units	Description	time of validity of the value
	SITELONG	rad or deg ?	Telescope longitude	static
	SITELAT	rad or deg ?	Telescope latitude	static
	RXHORI	radians ?	Nasmyth offset in Pointing Model	static
	RXVERT	radians ?	Nasmyth offset in Pointing Model	static
	RXHORICO	radians ?	Nasmyth offset in Pako (user defined)	static
	RXVERTCO	radians ?	Nasmyth offset in Pako (user defined)	static
	P1 .. P6	radians ?	Pointing Model parameters	static
	CTYPE1	string	Source coordinate system for BASELONG (e.g. AZ, RA, etc.)	static
	CTYPE2	string	Source coordinate system for BASELAT (e.g. EL, DEC, etc.)	static
	SYSTEMOF	string	System in which offsets (LONGOFF/LATOFF) are reported	static
	LONGOBJ	rad or deg ?	Longitude of the source in the chosen coordinate system (RA or AZ etc.)	predicted value at TimeStamp + 2s
	LATOBJ	rad or deg ?	Latitude of the source in the chosen coordinate system (DEC or EL etc.)	predicted value at TimeStamp + 2s
timeStamp		seconds ?	time at which the antMD message is sent
slowRate		Hz	Frequency at which the coordinates data are generated
LST	LST	seconds ?	Local Sideral Time	predicted value at TimeStamp + 2s
MJD	MJD	days	Modified Julian Day	predicted value at TimeStamp + 2s
paralact	PARANGLE	rad or deg ?	Paralactic angle ['VALUES ARE VISIBLY WRONG', would be good to go in the code, find how they are calculated and correct the mistake]	?
basisLat	BASELONG	radians ?	Actual longitude in the chosen coordinate system (RA or AZ etc.)	predicted value at TimeStamp + 2s
basisLong	BASELAT	radians ?	Actual latitude in the chosen coordinate system (DEC or EL etc.)	predicted value at TimeStamp + 2s
xOffset	LONGOFF	radians ?	Scan pattern longitude offset from the source in SYSTEMOF (RA or AZ etc.)	predicted value at TimeStamp + 2s
yOffset	LATOFF	radians ?	Scan pattern latitude offset from the source in SYSTEMOF (DEC or EL etc.)	predicted value at TimeStamp + 2s
actualAz	CAZIMUTH	radians ?	"Commanded" azimuth	TimeStamp-1s/slowRate
actualEl	CELEVATION	radians ?	"Commanded" elevation	TimeStamp-1s/slowRate
trackAz	AZIMUTH	radians ?	Real azimuth in the encoder reference	TimeStamp-1s/slowRate
trackEl	ELEVATION	radians ?	Real elevation in the encoder reference	TimeStamp-1s/slowRate
SigTrAz	TRACKING_AZ	radians ?	Azimuth RMS tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate
SigTrEl	TRACKING_EL	radians ?	Elevation RMS tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate
MaxTrAz		radians ?	Azimuth Max tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate
MaxTrEl		radians ?	Elevation Max tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate
MinTrAz		radians ?	Azimuth Min tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate
MinTrEl		radians ?	Elevation Min tracking error (sampling with fastRate = 128 Hz)	TimeStamp-1s/slowRate

Relation between the various coordinates variables

For simplicity I note Rot the rotation matrix which allows to switch from one coordinate system to another one, without specifying which are these coordinate system (to know this look at the values inside CTYPE1, CTYPE2 and SYSTEMOF) ==> this means that I do not distinguish between a rotation and its inverse operation, but the reader can figure out which is the direction of the rotation from the context. Note that Rot may use the paralactic angle, but since the value is wrong it can be recalculated using Az, El, and the Site Latitude.

I note PM the corrections from the pointing model applied to the wished coordinates, to build the commanded coordinates that will allow to point in the sky real coordinates that are as close as possible to the wished coordinates.

Also I don't write the transformation from one unit system to another (ex: rad to deg, etc.).

With this conventions we should have (TO BE CHECKED ON A FITS FILE AND/OR 30m EXPERTS [AS/WB/HU/RZ...]):

[BASELONG; BASELAT] = [LONGOBJ; LATOBJ] + [LONGOFF; LATOFF]
[BASELONG; BASELAT](T-2s) = Rot[CAZIMUTH; CELEVATION](T+1s/slowRate) ; Attention! The relation given here is what I think was the intention of people who created this set of coordinates, however as reported in the GISMONCSInterfaceandFITSFormatv0.5.pdf document, the experience of tracking errors with GISMO prior to 2012 indicates that some corrections are missing in [CAZIMUTH; CELEVATION], in particular the inclinometer corrections, and possibly other corrections...
[AZIMUTH; ELEVATION] = PM([CAZIMUTH;CELEVATION]) + [TRACKING_AZ; TRACKING_EL] ; As indicated also in GISMONCSInterfaceandFITSFormatv0.5.pdf they seem to be encoder values, not coordinates in the sky
Taking into account the remarks above and calling AZ and EL the real Azimuth in the sky and the real Elevation in the sky: [AZ; EL](T) = Rot[BASELONG; BASELAT](T-2s) + [TRACKING_AZ; TRACKING_EL](T+1s/slowRate)

-  ⇤ ← Revision 2 as of 2013-06-25 14:08:20 → 
  Size: 5507
  Editor: NikaBolometer
  Comment:
+   ← Revision 9 as of 2013-07-05 09:29:37 → ⇥
  Size: 7127
  Editor: NikaBolometer
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
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-=== Important preliminary remark: for now this page is a sand box where I gather various informations about coordinates variables generated by the 30m telescope control system, which may be useful for the implementation of a new instrument into the system.=== 
I gathered these information from various documents, Wiki pages, and email exchanges with specialists of the 30m telescope. Ideally I would like that this page contain the list of the various coordinates values delivered by the telescope, with their descriptions and the relations between them. It would good also to centralizes here links to related documents/wiki pages. Of course all this would have to be verified and approved by the 30m specialists (which is not the case for now).
+=== Important preliminary remark: for now this page is a sand box where I gather various informations about coordinates variables generated by the 30m telescope control system, which may be useful for the implementation of a new instrument into the system ===
I gathered these information from various documents, Wiki pages, and email exchanges with specialists of the 30m telescope. Ideally I would like that this page contains the list of the various coordinates values delivered by the telescope, with their descriptions and the relations between them. It would good also to centralizes here links to related documents and wiki pages.
 Line 16:
-||           || RXHORICO    || radians ?    || Nasmyth offset in user defined (Pako) || static ||
||           || RXVERTCO    || radians ?    || Nasmyth offset in user defined (Pako) || static ||
+||           || RXHORICO    || radians ?    || Nasmyth offset in Pako (user defined) || static ||
||           || RXVERTCO    || radians ?    || Nasmyth offset in Pako (user defined) || static ||
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+|| paralact  || PARANGLE    || rad or deg ? || Paralactic angle [''''VALUES ARE VISIBLY WRONG'''', would be good to go in the code, find how they are calculated and correct the mistake] || ? ||
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+Line 31:
-|| xOffset   || LONFOFF     || radians ?    || Scan pattern longitude offset from the source in SYSTEMOF (RA or AZ etc.)|| predicted value at TimeStamp + 2s ||
+|| xOffset   || LONGOFF     || radians ?    || Scan pattern longitude offset from the source in SYSTEMOF (RA or AZ etc.)|| predicted value at TimeStamp + 2s ||
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+Line 37:
-|| SigTrAz   || TRACKING_AZ || radians ?    || Azimuth RMS tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
|| SigTrEl   || TRACKING_EL || radians ?    || Elevation RMS tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
|| MaxTrAz   ||             || radians ?    || Azimuth Max tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
|| MaxTrEl   ||             || radians ?    || Elevation Max tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
|| MinTrAz   ||             || radians ?    || Azimuth Min tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
|| MinTrEl   ||             || radians ?    || Elevation Min tracking error (sampling with fastTrace = 128 Hz) || TimeStamp-1s/slowRate ||
+|| SigTrAz   || TRACKING_AZ || radians ?    || Azimuth RMS tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
|| SigTrEl   || TRACKING_EL || radians ?    || Elevation RMS tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
|| MaxTrAz   ||             || radians ?    || Azimuth Max tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
|| MaxTrEl   ||             || radians ?    || Elevation Max tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
|| MinTrAz   ||             || radians ?    || Azimuth Min tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
|| MinTrEl   ||             || radians ?    || Elevation Min tracking error (sampling with fastRate = 128 Hz) || TimeStamp-1s/slowRate ||
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+== Relation between the various coordinates variables ==
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+Line 46:
- Az(El)_real = Az(El)_expected + TRACKING_AZ(EL); Az(El)_expected = AZIMUTH(ELEVATION) ? but TRACKING_AZ(EL) and AZIMUTH(ELEVATION) are in encoder units {in IMBF-antenna}, so use BASELONG(BASELAT) [= source position in the system defined in CTYPE1(CTYPE2) {in IMBF-scan}] and LONFOFF(LATOFF) [= offset to the source position] ? Note that CAZIMUTH(CELEVATION) seem to be the intended coordinates, but the commanded ones are these corrected by the inclinometer values (and possible other corrections).
+For simplicity I note ''Rot'' the rotation matrix which allows to switch from one coordinate system to another one, without specifying which are these coordinate system (to know this look at the values inside CTYPE1, CTYPE2 and SYSTEMOF) ==> this means that I do not distinguish between a rotation and its inverse operation, but the reader can figure out which is the direction of the rotation from the context. Note that ''Rot'' may use the paralactic angle, but since the value is wrong it can be recalculated using Az, El, and the Site Latitude.

I note ''PM'' the corrections from the pointing model applied to the wished coordinates, to build the commanded coordinates that will allow to point in the sky real coordinates that are as close as possible to the wished coordinates.

Also I don't write the transformation from one unit system to another (ex: rad to deg, etc.).

With this conventions we should have (TO BE CHECKED ON A FITS FILE AND/OR 30m EXPERTS [AS/WB/HU/RZ...]):
 * [BASELONG; BASELAT] = [LONGOBJ; LATOBJ] + [LONGOFF; LATOFF]  
 * [BASELONG; BASELAT](T-2s) = ''Rot''[CAZIMUTH; CELEVATION](T+1s/slowRate) ; '''Attention! The relation given here is what I think was the intention of people who created this set of coordinates, however as reported in the GISMONCSInterfaceandFITSFormatv0.5.pdf document, the experience of tracking errors with GISMO prior to 2012 indicates that some corrections are missing in [CAZIMUTH; CELEVATION], in particular the inclinometer corrections, and possibly other corrections...'''
 * [AZIMUTH; ELEVATION] = ''PM''([CAZIMUTH;CELEVATION]) + [TRACKING_AZ; TRACKING_EL] ; '''As indicated also in GISMONCSInterfaceandFITSFormatv0.5.pdf they seem to be encoder values, not coordinates in the sky'''
 * Taking into account the remarks above and calling AZ and EL the '''''real Azimuth in the sky and the real Elevation in the sky''''': [AZ; EL](T) = ''Rot''[BASELONG; BASELAT](T-2s) + [TRACKING_AZ; TRACKING_EL](T+1s/slowRate)

Diff for "CoordinatesParamNCS"

Relation between coordinates parameters of the 30m telescope

Important preliminary remark: for now this page is a sand box where I gather various informations about coordinates variables generated by the 30m telescope control system, which may be useful for the implementation of a new instrument into the system

Table of the coordinates parameters generated by the New Control System of the 30m telescope

Relation between the various coordinates variables