[time-nuts] nuts about position
jimlux at earthlink.net
Wed Apr 25 23:39:31 EDT 2018
On 4/25/18 7:46 PM, Brooke Clarke wrote:
> Hi J:
> I had a number of survey stakes I placed using a manual transit and tape
> measure and hired a local surveyor to tell me where they were and also
> tell me where my GPS antenna was located.
> He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total
> station on another tripod and ran a cable between the two. After some
> time (tens of minutes or ??) he used the theodolite to sight my stakes
> and the GPS antenna. I got a report back in a week or so. Total cost a
> few hundred dollars.
> I'm in the process of looking at how accurate the GPS is in my new LG G6
Yep - A typical total station is good to "a few seconds" (some single
digit mm at 100 meters) in angle. Distance is usually pretty accurate
1.5 mm + 2ppm.
So over a typical 100m sort of size (several acres) a total station can
provide relative positions to better than a cm, but probably not better
than a mm.
A good optical theodolite can do *maybe* an order of magnitude better,
in terms of the basic measurement, but then there's other confounding
factors that might dominate.
For instance, are you sure you're holding the prism/target *precisely*
over the mark? And just what *is* that mark.
Precision metrology in any field is fascinating, but a rabbit hole down
which one can fall very, very deep.
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