stevensallyra1@... Mar 22, 2018
On 16 Mar 2018 7:46 p.m., "Bill Gray pluto@... [find_orb]" <find_orb@yahoogroups.com> wrote:Hi Steve,
On 2018-03-16 06:38, stevensallyra1@aol.com [find_orb] wrote:
> Many thanks for the information. Does that mean I need to set
> Astrometrica to 167 metre's rather than the 119 metres given
> by Google earth?
You could ask Herbert Raab about this, and he might tell
you that he's already computing the offset and converting your
119-m height above sea level to a 167-m height above the ellipsoid.
I don't really know how Astrometrica handles that issue (I didn't
know how MPC handled it until a few weeks ago).
-- Bill
> Thanks
>
> Steve
>
> On 14 Mar 2018 8:04 p.m., "Bill Gray pluto@projectpluto.com [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>
> > >
> > >
> > >
> >
> >
> >
> >
> >
>
>
>
>
>