[time-nuts] GPS position

[Wes]

Nothing to do with time but...

Technically speaking, in surveying a bench mark is a vertical control point.  In 
playing with Geocaching I've located bench marks that were placed in the 1930's 
and never found again (until I did).  There were often a hundred feet or more 
from where the description had them.  (Great fun BTW)

See: https://www.geocaching.com/mark/


On 5/2/2016 9:13 AM, Chris Albertson wrote:
> A man with a GPS knows where he is.  A man with two GPS' not not sure.
>
> I've always wanted to walk my self-survey GPS over to a brass USGS
> benchmark and see it the GPS matches to benchmark location.  OK, I've done
> this with a hand held GPS and gotten readings within about 10 meters.
>
> But before spending a lot of time removing the lat 10cm of error I'd do a
> test at the nearest BM that is not in the middle of a street.
>
> What has stopped me from doing this is that a few years ago I had to have
> my lot lines surveyed.  They got to better then 1/10 of a foot at each
> corner and shot  some brass markers into the concrete.    Google can see my
> house's roof ridge lines and the concrete so I can work out the exact
> location of the roof mount antenna to within maybe 18 inches.  It seems to
> agree with the survey as long as everyone uses WGS84.
>
>