[time-nuts] Time Transfer

Brooke Clarke brooke at pacific.net
Sun Dec 16 01:57:17 EST 2007


Hi Hal:

I had already driven wood stakes for three corners of an even second of lat and 
lon.
He setup the main tripod about 5 feet away from the corner in a random location 
and using a optical plummet drove a long nail with an ID disk into the ground.

Then about 100 feet away drove another nail into my driveway in a location that 
was sort of in a hole formed by my house and the trees.  (the corner above has 
a good view of the sky).

A second tripod was setup on the driveway above the nail and a second GPS 
receiver installed on it with a cable back to the first GPS receiver.

He got the receivers set up and doing what they do.  After maybe 5 or 10 
minutes the GPS receivers had a bearing between the two tripods.

Now he put a total station on the main tripod and sighted the driveway tripod 
and dialed in it's known bearing.  He measured the height of the main telescope 
pivot above the nail in the dirt.

Now he could point the transit at my stakes, the GPS antenna and a few new 
markers he put in and get the bearing and distance to them.

All that took maybe a few hours.

Then he went back to his office and post processed the data using a local CORS 
station and some flavor of WGS-84 with a year number after it.

A few days later I got a spread sheet showing the Easting and Northing needed 
to get from my stakes to the exact even seconds along with the elevations at 
those locations.

my antenna is at:
39:11:24:.5833 N
123:09:50.4842 W
920.14 feet.

If you put the Lat and Lon into Google Earth you can see exactly where the 
antenna is.

The prior antenna estimate was:
39:11:24.692
123:09:50.548
819.224 feet

A second of lat is about 100 feet anywhere so the delta Lat is about 10 feet
A second of lon at 39N is about 77.5 feet so the delta Lon is about 5 feet
The 100 feet elevation difference escapes me.
The stakes I put in the ground were based on the GPS antenna location and 
sighting Polaris at culmination.  They all were within a few feet.

I was asking for maybe an inch accuracy and 0.0001 of lat is about 1/10 of an 
inch.  But he didn't make any claims about how good the data was.  This is just 
for me not any legal reason.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Hal Murray wrote:
>>I hired the local surveyor who does  GPS to locate my antenna and a
>>few spots around the house that are on even second Lat and lon
>>numbers, like 39:11:25.00000.
> 
> 
> How long did it take him to get a fix?  What sort of accuracy does he claim?
> 
> How well did his data agree with your GPS?  Did you manage to sort out all 
> the grid options?
> 
> Last time I tried to sort out the grid options, I had 2 GPS units and a USGS 
> topo map.  That gave me 3 different answers.
> 
> 



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