[time-nuts] GPS altitude somewhat wrong?
henry at pericynthion.org
Wed Jun 8 18:21:32 EDT 2016
the address in your signature is close to the 5250 ft (geoidal)
On Wed, Jun 8, 2016 at 3:18 PM, Henry Hallam <henry at pericynthion.org> wrote:
> 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 the accuracy
> of a GPS altitude measurement should be better than about 20 meters.
> I'm not sure if the Thunderbolt counts as such.
> How flat is Boulder? Do you have a proper surveyed elevation of your location?
> On Wed, Jun 8, 2016 at 1:33 PM, Van Horn, David
> <david.vanhorn at backcountryaccess.com> 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?
>> David VanHorn
>> Lead Hardware Engineer
>> Backcountry Access, Inc.
>> 2820 Wilderness Pl, Unit H
>> Boulder, CO 80301 USA
>> phone: 303-417-1345 x110
>> email: david.vanhorn at backcountryaccess.com<mailto:david.vanhorn at backcountryaccess.com>
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