-----Original Message----- From: time-nuts [mailto:[email protected]] On Behalf Of Michael Perrett Sent: Wednesday, June 8, 2016 4:33 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] GPS altitude somewhat wrong?
A couple of things come to mind: 1) Is this a single measurement or an average over at least 24 hours? 60+ hours 2) Did you get your elevation via the receiver survey mode (recommended)? This is what's currently being displayed in LH after a 60 hour survey 3) How close is your "nominal" elevation measurement and what makes you think it is truth? Damifino. :) 4) The vertical component of the GPS position solution is typically 50% worse accuracy and a lot noisier than the horizontal measurement. If you have a good horizontal measurement it is unlikely you have a "wrong answer" on elevation since your receiver is using the same data, just solving the equation for a different variable. 5) What is your satellite mask angle? The geometry (hence accuracy) degrades as an increasing function with mask angle. Suggest for the survey mode you use as low a mask angle as possible (typically 5 to 10 degrees). Currently set to 5 degrees, which I know is low, but I wanted to see what the whole sky map looks like. I will dial it up as we get things settled in. Finally, your 214' error is outrageous. For a surveyed position the answer should be with +/- 10'. Ok.. Michael Perrett On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David < [email protected]> wrote: > > I have just installed a Thunderbolt here to get our time and frequency > equipment all on the same page. > As I was looking at the display on Lady Heather, I was noticing that > the GPS altitude seems rather wrong. > We are in Boulder CO, which is nominally 5430' and the antenna is > about 20' off the ground. > The display (near overdetermined position) reads 1589.72991 meters or > 5216 and change in feet. > Altitude is a big deal around here. :) > > I suppose 214' isn't that outrageous, but it does bring me to a question: > > How accurate is the altitude number really? > > Thanks. > > > -- > David VanHorn > Lead Hardware Engineer > > Backcountry Access, Inc. > 2820 Wilderness Pl, Unit H > Boulder, CO 80301 USA > phone: 303-417-1345 x110 > email: [email protected]<mailto: > [email protected]> > > _______________________________________________ > time-nuts mailing list -- [email protected] To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
