Re: [time-nuts] GPS altitude somewhat wrong?

Using the thunderbolt here. I only asked because a co-worker spotted the altitude and thought it was "wrong" for boulder. -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Mark Sims Sent: Thursday, June 9, 2016 10:56 AM To: time-nuts@febo.com Subject:

Re: [time-nuts] GPS altitude somewhat wrong?

Yo Hal! On Thu, 09 Jun 2016 02:12:53 -0700 Hal Murray wrote: > g...@rellim.com said: > > While you are waiting check out the attached scatter plot. Now > > THAT is a good $25 GPS! Beats the heck outta any Garmin. CEP(95) > > of 1.5 meters over 1,000 seconds. > >

Re: [time-nuts] GPS altitude somewhat wrong?

Yo Mark! On Thu, 9 Jun 2016 16:56:12 + Mark Sims wrote: > You have to be careful with a lot of modern GPS receivers. Many > implement some sort of "position pinning". If they do not detect > significant movement, they either stop updating the coordinates or >

Re: [time-nuts] GPS altitude somewhat wrong?

-Original Message- From: time-nuts [mailto:time-nuts-bounces+david.vanhorn=backcountryaccess@febo.com] 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

Re: [time-nuts] GPS altitude somewhat wrong?

:28 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] GPS altitude somewhat wrong? I just checked Google Earth and the elevation of your office is 5260', only about 24' off of your GPS estimate if that is your location. Michael On Wed, Jun 8, 2016 at 1:33 PM

Re: [time-nuts] GPS altitude somewhat wrong?

g...@rellim.com said: > While you are waiting check out the attached scatter plot. Now THAT is a > good $25 GPS! Beats the heck outta any Garmin. CEP(95) of 1.5 meters over > 1,000 seconds. What type of GPS was that? -- These are my opinions. I hate spam.

Re: [time-nuts] GPS altitude somewhat wrong?

I've had that query before too, but in that case it turned out to be that by default some receivers/software report Mean Sea Level and others Height Above Ellipsoid, or both. Angus. On Wed, 8 Jun 2016 20:33:58 +, you wrote: > >I have just installed a Thunderbolt here to get our time and

Re: [time-nuts] GPS altitude somewhat wrong?

Yo Tom! On Wed, 8 Jun 2016 19:26:21 -0700 "Tom Van Baak" wrote: > From one NW GPS farm to another... I'm willing to help you debug > yours. Nothing to debug. I know if I move the antenna I can do better, but it does what I need, and it is near the server that needs it.

Re: [time-nuts] GPS altitude somewhat wrong?

t: Wednesday, June 08, 2016 3:24 PM Subject: Re: [time-nuts] GPS altitude somewhat wrong? Yo David! On Wed, 8 Jun 2016 20:33:58 + "Van Horn, David" <david.vanh...@backcountryaccess.com> wrote: > I suppose 214' isn't that outrageous, but it does bring me to a > question: Look

Re: [time-nuts] GPS altitude somewhat wrong?

On Wed, Jun 8, 2016 at 4:33 PM, Van Horn, David < david.vanh...@backcountryaccess.com> wrote: > Backcountry Access, Inc. > 2820 Wilderness Pl, Unit H > Boulder, CO 80301 USA > Google Earth has the elevation of this address as 5272' which is a good deal closer to your reading... -- --Jim

Re: [time-nuts] GPS altitude somewhat wrong?

Some of that is probably the difference between the geoid (what your surveyed maps report height relative to) and the WGS84 ellipsoid (what your GPS reports heights relative to). At Boulder that difference is only about 15 meters, though. Generally with VDOP < 2 and a reasonably modern

Re: [time-nuts] GPS altitude somewhat wrong?

I just checked Google Earth and the elevation of your office is 5260', only about 24' off of your GPS estimate if that is your location. Michael On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David < david.vanh...@backcountryaccess.com> wrote: > > I have just installed a Thunderbolt here to get our

Re: [time-nuts] GPS altitude somewhat wrong?

On Wed, June 8, 2016 3:33 pm, Van Horn, David wrote: > How accurate is the altitude number really? Probably not the question you really want to ask. Try "what does GPS mean by altitude? Altitude relative to what standard?" http://www.esri.com/news/arcuser/0703/geoid1of3.html -- Chris Caudle

Re: [time-nuts] GPS altitude somewhat wrong?

Per https://www.topoquest.com/map.php?lat=40.02486=-105.24468=nad27=2=auto=d=zoomin=m the address in your signature is close to the 5250 ft (geoidal) contour. Henry On Wed, Jun 8, 2016 at 3:18 PM, Henry Hallam wrote: > Some of that is probably the difference between the

Re: [time-nuts] GPS altitude somewhat wrong?

Yo David! On Wed, 8 Jun 2016 20:33:58 + "Van Horn, David" wrote: > I suppose 214' isn't that outrageous, but it does bring me to a > question: Looking at my GPS farm, fair but not great skyview. A Garmin 18x reports: Altitude Err:+/- 264 ft

Re: [time-nuts] GPS altitude somewhat wrong?

Some of that is probably the difference between the geoid (what your surveyed maps report height relative to) and the WGS84 ellipsoid (what your GPS reports heights relative to). At Boulder that difference is only about 15 meters, though. Generally with VDOP < 2 and a reasonably modern receiver

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? 2) Did you get your elevation via the receiver survey mode (recommended)? 3) How close is your "nominal" elevation measurement and what makes you think it is truth? 4) The vertical component of