[Kstars-devel] SatLIb verification

[Bernard GODARD]

On 5/1/07, Bernard GODARD <bernard.godard at gmail.com> wrote:
> I've just modified my test program to find all the HST passes on a ten
> day period using SatFindPosition and keeping only the data where
> elevation is above 10 degrees and I found all the passes predicted by
> heavens above but some of them were flagged as being in Sun light
> (visibility = '*') but not being on the night side (visibility = '+')
> whereas Heavens above gave a sun altitude at maximum elevation
> negative. It seems the sun sets later in SatLib.
>
> Heavens above seems to report only passes with altitude > 10 degrees.
> That's why SatNexPass in SatLib reports much more passes (elevation >
> 0)
>
>
> On 5/1/07, Bernard GODARD <bernard.godard at gmail.com> wrote:
> > Hi,
> >
> >
> > On 5/1/07, Jason Harris <kstars at 30doradus.org> wrote:
> > > Hi,
> > >
> > > So do I have an old version of SatLib or something?  Because when I
> > > run the demo, I am seeing some problems.
> >
> > I did my test with the SatLib.h and SatLib.c code I found in the
> > satlib directory of kstars svn. I didn't use the demo code. I made a
> > custom C test program.
> >
> > > First of all, It reports a
> > > Julian Day number that is off by about a month (and calendar dates
> > > reported in the output tables also reflect this month-old date).  I
> > > have to hack the code like this if I want the correct JD:
> > >
> > > jd=Julian_Date(cdate) + 30.0;
> > Just tested. same problem here!
> >
> > >
> > > There are some ambiguities in the meanings of some parameters:
> > > + What time is reported by the demo?  I assume it's UT, and looking at
> > > the code I'm pretty sure that is correct.
> >
> > That's what I did too.
> >
> > > + What convention is used for geographic longitude?  Are west
> > > longitudes positive or negative?  From the longitude you gave for
> > > Toulouse, I guess west longitudes are negative.
> > >
> > I was wrong about that but the difference is not so important for
> > Toulouse because it's almost zero longitude. I just did the test with
> > west longitude positive and I have now a better match of the Heavens
> > Above results.
> >
> > > Assuming my guesses are correct, as I said before, I can't find any
> > > correlation between SatLib predictions and those of
> > > NASA/Heavens-above/calsky.
> > >
> > > For example, for JD=2454221.5 from Tucson, AZ (lat=32.222,
> > > long=-110.926), SatLib gives the following pass prediction for HST:
> > >
> > > % ./demo HST
> > > JD=2454221.516105
> > > 90037B HST 2007-05-01 12:15:10   0.03 185.72  38   9  251   2727  73294 +
> >
> > I have tried to re-do your test and it seems SatLib's demo finds many
> > more passes than Heavens Above.
> >
> > But I did another test with my test program which doesn't use
> > SatNextPass but SatFindPosition and I made it print the epheremeris
> > for the 3 may 19h30 (local time = GMT-7) pass above Tucson (
> > 32.2220°N, 110.9260°W, alt 751m) predicted by Heavens Above and I have
> > a very close match.
> > _________________________________________________________________________
> >
> > test program
> > _________________________________________________________________________
> >
> > #include "SatLib.h"
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <math.h>
> >
> >
> > #define NBPTS 3600
> >
> >
> >
> > int main(int argc, char *argv[]){
> >
> > char *sat1 = "HST";
> > char *obsname = "Tucson";
> > double latitude = 32.222;
> > double longitude = 110.926;
> > double altitude = 751.0;
> > char *TLE_file = "hst.tle";
> > int result = 0;
> > double jd_start = 2454224.60417;
> > double step = 1;
> > int i=0;
> > int h,m;
> > double s,s1,s2;
> > double t;
> > SPositionSat * pPositionSat[NBPTS];
> >
> > for (i=0;i<NBPTS;i++)
> >   pPositionSat[i] = (SPositionSat *) malloc(sizeof(SPositionSat));
> >
> > result = SatInit(obsname, latitude, longitude, altitude, TLE_file);
> > result = SatFindPosition(sat1, jd_start, step, NBPTS, pPositionSat);
> >
> > for (i=0;i<NBPTS;i++){
> >   t = (jd_start-0.5)+i*step/86400.0;
> >   s1 = (t - floor(t))*86400;
> >   h = floor(s1/3600.0);
> >   s2 = s1 - h*3600.0;
> >   m = floor(s2/60.0);
> >   s = s2 - m * 60.0;
> >
> >   printf("UT TIME : H: %d, M: %d, S : %f, ALT : %f, AZIM : %f VISI:
> > %c\n",h,m,s,pPositionSat[i]->sat_ele,pPositionSat[i]->sat_azi,pPositionSat[i]->visibility);
> > }
> >
> >   return 0;
> > }
> >
>