I posted about running a long baseline earlier and using an "assumed" height reading for my rods.

WELL . . . I actually measured my GPS rods and they're 6.75 feet.

NOW a 33 minutes occupation
a 14.2 mile baseline
a PDOP of 2.7
the software reports errors of : 0.149'east, 0.151' north, 0.153' vertical.

I used a county perm mon and let the CORS station(14.2 miles away) to float, "just to see".

I get a difference of: 0.001'east, 0.033'north, 0.05' vertical.

THIS IS WITH 33 minutes and a PDOP of 2.7.

ABSOLUTELY UNREAL.

Look at the facts:

It will not always be this good. When all the sats are in view, it may even do better. When they are clumped up at one end of the sky, you will be doing good to get within a foot.

So, my point is:

IF the point matters, get a 2 HR observation. This almost always eleminates the need to return. And you also have enough data to play with it a little. Such as drop out a sat, or raise the elev. mask. Or trim out some dirty data.

So, that is how I do it. With 6 recievers, Target is 2 hrs of data.

Hope this advice helps.

Nate

Actually Nate, I rarely use the CORS station since there's usually a county monument with a couple of miles.

I really only use the CORS station as a further check.

I'm just really saying that it's ONE HELL OF A CHECK FOR 14.2 MILES AND 33 MINUTES.

How far away from a CORS would be to far to use it? I live about 80 miles from the station at the Jacksonville Airport.

Dave to get a decent number, you are looking at a 4 hour occupation.

There are actually 2 one second CORS stations in Jacksonville. JXVI at Jacksonville Airport and ZJX1 at Hiiliard Airport. Use both to set your self some control around town. The 30 second CORS in Savannah should help out on a long occupation.

But if you have any long occupation and a local control point, checking against the CORS can never hurt.

Paul in PA

Paul, I appreciate the information. I think I'll set one up at the office tomorrow night and let it go till morning.

David
Modified By David Tomberlin on 3/19/2004 at 12:32 AM

I just downloaded GARF data for my mentioned baseline. Garf(COR) is 33.4 miles west from my control. GUST(COR) is 14.2 miles east of my control.

I had a 33 minute session(same as to the GARF(COR).

The results? Less than 0.10' easting and northing and 0.10 off in the ellipsoid hgt.

Now . . . I held the County Monument and let both GUST(COR/14.2 miles) and GARF(COR/33.4 miles) float.

33 minutes of occupation

the solution to GARF was a "partial", but hey . . . it was only 33 minutes.

The reported errors to GARF were in the neighborhood of about 0.35east and 0.35' north.
Modified By John Francis on 3/19/2004 at 10:45 AM