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INDI Library v1.8.1 Released (09 Sep 2019)

Monthly maintenance release INDI v1.8.1

Calculate and Apply Custom Tracking Rates from Ephemeris Data

7 months 2 weeks ago 7 months 2 weeks ago by Ihoujin.
Ihoujin
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #34281
I'm just putting this idea out there for future development. Tracking comets and asteroids would benefit from accurate custom tracking rates that can be calculated from ephemeris data. This feature is already part of EQmod on Windows but requires several manual steps to prepare. While INDI EQMod does supports custom tracking rates, I would love to some day see a fully integrated tool that can calculate the custom tracking rates for minor bodies and apply them.

INDI/KStars on Raspberry Pi 3B+
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Skywatcher HEQ5 Pro Mount
Canon 600D Camera
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3 months 3 weeks ago
Ihoujin
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39368
I found that the JPL Solar System Dynamics - Horizons System will provide difference in RA and Dec rates for minor bodies in units of Arcsec/hour. Converting them to Arcsec/s by a factor of 3600 and adding that to the Sidereal Rate (RA:15.041 & Dec:0) as a custom tracking rate would make it possible to easily follow moving targets such as comets and asteroids. I would not be surprised if this information is already available with the service KStars is using to get Comet and Asteroid positions.

The JPL SSD - Horizons system can be accessed via a web interface, Telnet service, and Email service. My wish is for KStars to fetch the current differential tracking rate via telnet and apply it as a custom rate automatically when tracking monor bodies. Lunar tracking could also be made more accurate by accounting for DEC rates that vary slightly at different latitudes due to parallax.

From the example below:
Date__(UT)__HR:MN     dRA*cosD d(DEC)/dt
 2019-May-23 00:00 *   29.25040  -38.5810
dRA*cosD=29.25040 arc"/hour = 0.0081251 arcs/s
Custom RA Rate: 15.041+0.0081 = 15.049
Custom Dec Rade: 0 + -0.0107

Example object information:
*******************************************************************************
Ephemeris / WWW_USER Thu May 23 03:01:37 2019 Pasadena, USA      / Horizons    
*******************************************************************************
Target body name: 123P/West-Hartley               {source: JPL#K192/3}
Center body name: Earth (399)                     {source: DE431}
Center-site name: (user defined site below)
*******************************************************************************
Start time      : A.D. 2019-May-23 00:00:00.0000 UT      
Stop  time      : A.D. 2019-Jun-22 00:00:00.0000 UT      
Step-size       : 1440 minutes
*******************************************************************************
Target pole/equ : No model available
Target radii    : (unavailable)                                                
Center geodetic : 284.330000,45.4200000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 284.330000,4484.46453,4520.2328 {E-lon(deg),Dxy(km),Dz(km)}
Center pole/equ : High-precision EOP model        {East-longitude positive}
Center radii    : 6378.1 x 6378.1 x 6356.8 km     {Equator, meridian, pole}    
Target primary  : Sun
Vis. interferer : MOON (R_eq= 1737.400) km        {source: DE431}
Rel. light bend : Sun, EARTH                      {source: DE431}
Rel. lght bnd GM: 1.3271E+11, 3.9860E+05 km^3/s^2                              
Small-body perts: Yes                             {source: SB431-N16}
Atmos refraction: NO (AIRLESS)
RA format       : HMS
Time format     : CAL 
EOP file        : eop.190522.p190813                                           
EOP coverage    : DATA-BASED 1962-JAN-20 TO 2019-MAY-22. PREDICTS-> 2019-AUG-12
Units conversion: 1 au= 149597870.700 km, c= 299792.458 km/s, 1 day= 86400.0 s 
Table cut-offs 1: Elevation (-90.0deg=NO ),Airmass (>38.000=NO), Daylight (NO )
Table cut-offs 2: Solar elongation (  0.0,180.0=NO ),Local Hour Angle( 0.0=NO )
Table cut-offs 3: RA/DEC angular rate (     0.0=NO )                           
*******************************************************************************
Initial IAU76/J2000 heliocentric ecliptic osculating elements (au, days, deg.):
  EPOCH=  2457126.5 ! 2015-Apr-14.0000000 (TDB)    RMSW= n.a.                  
   EC= .449300743971303    QR= 2.125967382318402   TP= 2455748.0628062398      
   OM= 46.53866425047554   W= 102.894694868525     IN= 15.35366879558836       
  Equivalent ICRF heliocentric equatorial cartesian coordinates (au, au/d):
   X= 4.657105285458996E+00  Y=-1.941203038292526E+00  Z=-2.417870194368305E+00
  VX= 2.829504245640315E-03 VY= 4.087231519282237E-03 VZ= 2.101437381881136E-03
Comet physical (GM= km^3/s^2; RAD= km):                                        
   GM= n.a.                RAD= n.a.                                           
   M1=  8.2      M2=  13.8     k1=  18.    k2=  5.      PHCOF=  .030           
Comet non-gravitational force model (AMRAT=m^2/kg;A1-A3=au/d^2;DT=days;R0=au): 
   AMRAT=  0.                                      DT=  0.                     
   A1= -2.738727331161E-9  A2= 7.358073592186E-9   A3= 0.                      
 Standard model:                                                               
   ALN=  .1112620426   NK=  4.6142   NM=  2.15     NN=  5.093    R0=  2.808    
*******************************************************************************
 Date__(UT)__HR:MN     dRA*cosD d(DEC)/dt
*****************************************
$$SOE
 2019-May-23 00:00 *   29.25040  -38.5810
 2019-May-24 00:00 *   29.85669  -38.5969
 2019-May-25 00:00 *   30.45272  -38.6091
 2019-May-26 00:00 *   31.03869  -38.6178
 2019-May-27 00:00 *   31.61476  -38.6231
 2019-May-28 00:00 *   32.18106  -38.6252
 2019-May-29 00:00 *   32.73773  -38.6242
 2019-May-30 00:00 *   33.28488  -38.6202
 2019-May-31 00:00 *   33.82260  -38.6134
 2019-Jun-01 00:00 *   34.35094  -38.6037
 2019-Jun-02 00:00 *   34.86987  -38.5912
 2019-Jun-03 00:00 *   35.37933  -38.5760
 2019-Jun-04 00:00 *m  35.87914  -38.5580
 2019-Jun-05 00:00 *m  36.36908  -38.5373
 2019-Jun-06 00:00 *m  36.84890  -38.5137
 2019-Jun-07 00:00 *m  37.31837  -38.4874
 2019-Jun-08 00:00 *m  37.77730  -38.4582
 2019-Jun-09 00:00 *m  38.22559  -38.4262
 2019-Jun-10 00:00 *m  38.66329  -38.3915
 2019-Jun-11 00:00 *m  39.09052  -38.3541
 2019-Jun-12 00:00 *m  39.50754  -38.3143
 2019-Jun-13 00:00 *m  39.91468  -38.2721
 2019-Jun-14 00:00 *m  40.31235  -38.2277
 2019-Jun-15 00:00 *m  40.70099  -38.1814
 2019-Jun-16 00:00 *m  41.08109  -38.1333
 2019-Jun-17 00:00 *   41.45310  -38.0835
 2019-Jun-18 00:00 *   41.81747  -38.0322
 2019-Jun-19 00:00 *   42.17459  -37.9795
 2019-Jun-20 00:00 *   42.52481  -37.9256
 2019-Jun-21 00:00 *   42.86841  -37.8705
 2019-Jun-22 00:00 *   43.20564  -37.8143
$$EOE

INDI/KStars on Raspberry Pi 3B+
Lubuntu 16.04
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG @280mm Guide Scope
PHD2
Adafruit Motor Hat shield
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.
The following user(s) said Thank You knro

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3 months 3 weeks ago
knro
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39369
Good idea. It's possible to add a web-interface to get this, though I'd really like to see this in the offline version.

KStars is still using VSOP87 for all solar system calculations. I toyed with the idea of using JPL ephemerides in KStars, but it was a lot of work and I was hoping I could have it as a Google Summer of Code project but no one applied.

Some details here on using the JPL ephemerides: www.projectpluto.com/jpl_eph.htm

Jasem Mutlaq
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3 months 3 weeks ago
wvreeven
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39370
Jasem, I have Java code that computes the rectangular position and velocity of a solar system body based on the Chebyshev components of either the JPL or INPOP ephemerides. It probably shouldn't be too much effort to transform those to C++, but my C++ coding is rusty to say the least. Please PM me if you'd like me to try to do the code conversion. I'd probably need a LOT of help though...


Wouter

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3 months 3 weeks ago
knro
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39371
I think a better long-term solution is to implement a JPL ephemerdis backend alongside VSOP87... though it's a lot of work :D

Jasem Mutlaq
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3 months 3 weeks ago
wvreeven
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39372
I agree. The VSOP87 backend should stay there and a JPL backend should be added. Some switch somewhere should allow for switching between the two. In any case, the offer stands so let me know if you can use my help, even if at first it may be limited.


Wouter

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3 months 3 weeks ago
Ihoujin
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Calculate and Apply Custom Tracking Rates from Ephemeris Data #39374
Thank you Jasem and Wouter!
It might be possible to calculate the dRA and dDec from the Orbital elements information provided by VSOP87, but as far as I know these are black boxes to me. I attempted to research how they are calculated but came up empty.

INDI/KStars on Raspberry Pi 3B+
Lubuntu 16.04
Skywatcher HEQ5 Pro Mount
Canon 600D Camera
Orion SSAG @280mm Guide Scope
PHD2
Adafruit Motor Hat shield
Adafruit GPS Module
Generic Bluetooth Joystick.
Startech 7 port powered USB Hub.

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