On 14 Mar 2018 8:04 p.m., "Bill Gray pluto@... [find_orb]" <find_orb@yahoogroups.com> wrote:

 

Hi Steve,

On 2018-03-14 07:44, stevensallyra1@aol.com [find_orb] wrote:

> You mention height above sea level, and the two ways of getting a
> true one. Is this something all observatories should consider and use?

If you get a code from MPC, they'll take care of the problem for
you. Gareth Williams tells me that if a position comes in from
Google Earth, they'll know it's an "above sea level" (or, equivalently,
above the geoid) measurement. He then computes the difference between
ASL and the ellipsoid (the "geoid height"), which can be up to about
a hundred meters. In your case, entering your lat/lon at

https://geographiclib.sourceforge.io/cgi-bin/GeoidEval

tells us the geoid height is about 48 meters: you're 119 meters
above mean sea level, but about 167 meters above the ellipsoid.
(Checking 'ObsCodes.html', I see that the correction was applied.)

GPS units usually just give ellipsoidal altitudes. Those can be
used without correction. (Which is the main reason MPC asks you to
tell them the source of your observatory's coordinates.)

Whether you should worry about a hundred meters depends on what
you're doing. Observe an object as far away as the moon, and it'll
make a maximum difference of 0.05", which is on the edge of causing
a noticeable systematic error. Observe closer objects, and it can
matter a lot. Observe navigation satellites, as some people are
doing to test how good their timing is :

https://www.projectpluto.com/gps_expl.htm

and even an error of a few meters can (in some cases) be noticed.
Such observers have to be added to 'rovers.txt', simply because the
'ObsCodes.html' format only has a precision of about six meters.

-- Bill

>
> Thanks
>
> Steve
>
> On 13 Mar 2018 4:31 p.m., "Bill Gray pluto@projectpluto.com [find_orb]" <find_orb@yahoogroups.com> wrote:
>
> Hi Steve,
>
> Aha! That code really ought to be in the list of actual,
> authorized MPC codes. And it is, but I think it must have
> been added in the last few days, along with four other new codes.
>
> If you download this file to your Find_Orb directory :
>
> https://www.minorplanetcenter.net/iau/lists/ObsCodes.html
>
> you should be all set. Run the program, and your astrometry
> shouldn't cause an error message to pop up.
>
> The initial "funding" for Find_Orb started out somewhat
> indirectly, through sales of my Guide desktop planetarium
> software. That caused me to write code for most of the
> underlying functions (planetary ephemerides, coordinate
> and time systems, etc.) So when I decided that I was curious
> about orbit determination, I had most of the bits and bobs
> already sitting on my hard drive.
>
> I posted the result, thinking it would mostly appeal to
> others interested in orbit determination and using it for
> educational purposes. That's happened, but it turned out
> to be of greater interest to observers. That resulted in some
> effort to make the program suitable for use by sleep-deprived
> people at telescopes in the middle of the night, ideally
> without too much frustration. (As with any software, it's
> important to know your users!)
>
> For some years, development of the program was based
> solely on my adding things in which I was interested. That
> eventually led to my getting some contracts to add still more
> improvements, which has really pushed things along nicely
> in the last few years.
>
> -- Bill
>
> On 2018-03-13 04:31, stevensallyra1@aol.com [find_orb] wrote:
> >
> >
> > Hi Bill,
> > Many thanks for your prompt reply. Much Appreciated.
> > My MPC observatory code is Z34
> > Coordinates  Long. 0 53 15.7 W,  Lat. 52 18 07.2 N  Alt..119 metres Google Earth   (as close as you can enter into Astrometrica  0.8877 W 52.3020 N.)
> >  I take it that the rovers.txt file then just needs replacing with the file you are going to amend and send to me?
> > Thanks and kind regards
> > Steve
> > PS What a great little program FindOrb is. Do you run by donations?
> > -----Original Message-----
> > From: Bill Gray pluto@projectpluto.com [find_orb] <find_orb@yahoogroups.com>
> > To: find_orb <find_orb@yahoogroups.com>
> > Sent: Mon, 12 Mar 2018 22:00
> > Subject: Re: [find_orb] Fwd: Update observatory list
> >
> > Hi Steve,
> >
> > You should update 'rovers.txt', for several reasons.
> >
> > 'ObsCodes.htm' is the MPC's list of observatories :
> >
> > https://www.minorplanetcenter.net/iau/lists/ObsCodes.html
> >
> > 'rovers.txt' is Find_Orb's list of additional observatories.
> > Unlike the MPC's file, you can specify your observatory in
> > latitude and altitude instead of in parallax constants, and
> > your coordinates can be in decimal degrees or in "traditional"
> > base-60 degrees/minutes/seconds. Also, the file itself
> > contains documentation on how to add new codes.
> >
> > Further comments at
> >
> > https://projectpluto.com/find_orb.htm#obs_codes
> >
> > Not mentioned there, but: you may want to send me your
> > position. I'll add it to 'rovers.txt'. The advantage of this
> > is that if you update Find_Orb, you won't lose the observatory
> > code you've added.
> >
> > -- Bill
> >
> > On 2018-03-12 14:01, stevensallyra1@aol.com <mailto:stevensallyra1@aol.com> [find_orb] wrote:
> > >
> > > Hi,
> > >
> > > Please advise the steps needed to update the observatory list on FindOrb.
> > > There seem to be two files in the FindOrb directory that need updating. Why two ?
> > >
> > > I'm not too sharp on computers!
> > >
> > > Thanks
> > >
> > > Steve
> > >
> > >
> > > ---------------------------
> > > Posted by: stevensallyra1@aol.com <mailto:stevensallyra1@aol.com>
> >
> >
> >
>
>
>
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>