[time-nuts] nuts about position

Brooke Clarke brooke at pacific.net
Wed Apr 25 14:18:30 EDT 2018

Hi Tom:

I have a friend who bought a house on a hill so that he could build an observatory with an excellent view of the sky.  
The telescope mount is the Paramount by Software Bisque.  This mount is capable of pointing accuracy measured in a small 
number of arc seconds.  That implies the control software knows the time to a high precision. But there's no "time nuts" 
clock involved.  The control PC computer only has the stock NTP function turned on the in the clock.

To get that pointing accuracy he uses TPoint software that models the mechanical errors in the mount.  As part of the 
start up procedure he points to a know star or stars and that sets the clock.  I expect that the location of the 
telescope is determined as part of the TPoint alignment process that looks at a large number of stars.

PS We used the gun laying function of the DAGR GPS receiver when laying out the observatory to get a North-South line.

As part of a FireWise community mapping process I'd like to get GPS coordinates of the fire hydrants (Lat, Lon, Ele).  
Is there a civilian GPS receiver that makes use of WAAS and/or DGPS corrections?

Have Fun,

Brooke Clarke

-------- Original Message --------
> List -- I had a recent query by a researcher who would like to pinpoint the location of his telescope(s) within 0.3 meters. Also (he must be a true scientist) he wants to do this on-the-cheap. He may have timing requirements as well, but that's another posting.
> So I toss the GPS question to the group. Surely some of you have crossed the line from precise time to precise location?
> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D position?
> When we run our GPSDO in survey mode how accurate a position do we get after an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have any of you compared that self-reported, self-survey result against an independently measured professional result or known benchmark?
> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot accuracy given enough time?
> If not, what improvement would -T models and RINEX-based web-service post-processing provide?
> It that's still not close enough to 0.3 m, is one then forced to use more expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to achieve this level of precision? If so, how cheaply can one do this? Or is the learning curve more expensive than just hiring an survey specialist to make a one-time cm-level measurement for you?
> Something tells me 1 foot accuracy in position is possible and actually easier than 1 ns accuracy in time. I'm hoping some of you can help recommend solution(s) to the researcher's question or shed light on this interesting challenge.
> Thanks,
> /tvb
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