The pnt command

    The pnt command has been added to the aotcl interpreter in vxWorks (used for online datataking).

Other documentation:

• within the online tcl interpreter pnt ? will return a help message showing the command and its options (pnt ?)
• online or offline helpdt pntcb will show a short explanation of using the pnt command (helpdt pntcb)
  

05jul13: Ephemeris tracking

Links:
Create ephemeris file
Load ephemeris file with pnt ephm ld
Track the ephemeris file

    Ephemeris tracking was added to the  pnt command on 05jul13. It allows you to use the pnt tr  command to track an ephemeris. This adds the capability of offsets and rates relative to an ephemeris position.
The new command   includes loading an ephemeris file and then tracking using this file.
    This can be used for:

• radar tracking of objects (although they may want to continue with how they currently track objects)
• tracking  objects such as the moon, satellites, or planets for calibration purposes.

How it works:

• The user specifies an ephemeris file using some pnt commands (see below).
• The user then starts the ephemeris tracking  by issuing the pnt track command:
• pnt tr 1 2 -c{E,R,T}     see below for def of E,R,T 
• Note that 1 2 are placeholders that must be entered, but are then ignored (these are normally the ra,dec requested).
• The coordinate options are J2000 (rcv) or current ra,dec (receive or transmit ephemeris).
  
• The pnt program will then:
• Each second is will linear interpolate to the position for  that second using the two ephemeris entries that bracket the current time.

 Steps to using an ephemeris file for tracking:

• Create an ephemeris file:
• This can be a standard radar ephemeris
• it contains the standard date, time , receive and transmit info from the ao radar ephemerides.
  
• The obs_tbl.sc script will down load an ephemeris from jpl horizons.
• The routine hortoao.pl will then convert  from horizon's  to ao ephemeris format.
• This ao short format contains: date time ra dec and optional values
  
• Normally this script is used for non radar work. By default it downloads a receive ephemeris.
• Notes on ephemeris files:
• lines that start with # are comments
  
• If multiple blocks are contained in the file then they must be separated by at least 1 comment line
• Within a given block the spacing between entries must be constant.
• When loading  an ephemeris file, a maximum of 720 entries can be loaeded.
  
• You must place the ao ephemeris file in a location that datataking can  access (see below)
• -->Warning<--
• The obs_tbls.sc script by default requests Apparent coordinates..
• this is -q type  of 2...
  
•  This means you need to use -cR for the pointing coordinates
• To use J2000 -cE coordinates you need
  
• obs_tbl.sc -q 1,4,20 ..(the 1 gives J2000). 
  
• then you use -cE
• If you used -cE with -q 2  with -cE coord system ,you will apply the precession, nutation, aberation correction twice.. as of 2016 that's about 12amin..
  
• Tell the pointing program to load the ephemeris
• The following pnt command will load an ephemeris:
• pnt ephm  ld type filename {yymmdd secMid}
• type- type of ephemeris file
• 1 -  standard ao radar ephemeris
• 2 -  Short ao ephemeris format (output from hortoao.pl)  eg:
•             date            ddtimeUTC  RA            Dec             az            el
  
• 2013-07-05 12:38:00 045108.82 +200140.4   81.7981  65.0676
• Where az,el are default optional values
• When loading, the receive ephem info is copied into the transmit ephem array.
  
• filename - filename for ephemeris file
• If no directory is included then it will search in /share/olda/Ephm/
• If a directory is supplied then it must  be  accessible from vxWorks (the users project directory: /share/obs4/usr/projId is ok)
• {yymmdd secMid} optional AST time in ephemeris to start loading.
• If not supplied then  the routine will use the current time
• Notes
•  if the time is after the end of a block, and a following block exists, it will start on the following block.
• Tell the pointing program to  track the loaded ephemeris file.
• You must first load an ephemeris
• the pnt tr command typically has a set of positions followed by optional offsets and rates. eg:
• pnt tr   192313.1 153131 -cJ -o 0 -.1 -cS -r 0. .01 -cs
• -c  defines the coordinate system
• -o starts the offset field
• -r starts the rate field
• Ephemeris tracking has added 3 new coordinate systems:
• -cE  J2000 ephemeris tracking. This tracks the receive ephemeris
• -cR  current ra,dec . this tracks the receive ra, dec.
  
• -cT   current ra,dec. This tracks the transmit ra,dec 
• Notes:
• When -cE is used then the ephemeris file must have had j2000 coordinates
• When -cT or -cR is used then the ephemeris file must have had current (of date) ra,dec.
• Track the ephemeris:
• pnt tr 1 2 -cR
  
• Note that the first two args 1,2 are required, but they are ignored
• pnt tr 1 2 -cT -o 0. -.1 -Cs
• track Tx ephemeris with -.1 great circle offset in za
• pnt tr 1 2 -cE -o 0 -.1 -cs -r 0 .01 -cs
• track J2000 ephemeris with -.1 offset in za and .01 rate in za.
• Examples:
• Load1998QE2 ephemeris from standard directory, and then start tracking the tranmist location:
• pnt ephm ld 1 1998QE2.s26
  
• pnt tr 1 2 -cT
• Notes: this starts loading from the current time.
• Create moon ephemeris for 05jul113, load, and track
• Offline:
• obs_tbl.sc -start 2013 130705 0000 -end 130705 2359 301 moon.hor
• Note obs_tbl.sc uses UTC date,times
• hortoao.pl < moon.hor > moon.ao
• chmod a+r  moon.hor   .. make sure datataking can read it.
  
• mv moon.ao /share/obs4/usr/x101/moon.ao
• Online when moon is rising
• pnt ephm ld 2 /share/obs4/usr/x101//moon.ao
• pnt tr 1 2 -cR   .. track the moon
  
• File locations:
• obs_tcl.sc is currently being debugged.
  
• /share/megs/phil/x101/ephm/obs_tbl.sc
• hortoao.pl is currently being debugged
  
• /share/megs/phil/x101/ephm/hortoao.pl

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