Thursday I started a control network on a 160+ acre tract, mostly pasture with the exception of boundary lines and corners. Typical. I ran the 5 point preliminary control with Locus units, and Friday decided to build another point. The network was built with good redundancy throughout.
As the survey proceeded we determined that an adjoiner corner in fairly dense woods would be a very good accessory point for our boundary reconstruction. As we are a bit under the gun, so to speak, to complete this project by 10/31, an executive decision was made to attempt to gps this point rather that cut 1000 feet of briars and saplings (on property other that our clients) and do conventional. Minimum of 2 hours field crew time we just couldn't spare.
So, I decided to try the 10 channel ProMark2 receivers. I used two receivers on points established for the original network and set one on the target point under moderate canopy. Trees a mix of pines, oaks, sweet gum and elm. We cut out the trees within 10 feet or so, fortunately all small trees. I was setting up the target unit at sunrise, with a flashlight this morning. The three units had a session of 1 hour 25 minutes together. For comparison's sake I'll give the fractional portion of the coords derived for the target point.

1. Holding fixed coords for both network points the target point had NORTH 0.966 and EAST 0.585

2. Holding fixed coordinates for point 1 of the network the target point had NORTH 0.973 and EAST 0.558.

3. Holding fixed coordinates for point 2 of the network the target point had NORTH 0.981 and EAST 0.545

After deciding these were "safe" to throw into the mix in the main data file the final coordinates of the target point were NORTH 0.970 and EAST 0.548.

Close enough for the project. I wonder though, under the same conditions what results I'd have gotten with the Locus units. The 9-10 sv's received by the PM2 under the trees may be the difference, especially considering how chopped the data was due to loss of lock.

Once again, I'm impressed with the ProMark 2 system.

J.D. Billings

J.D., How about creating a couple of new projects. In one project use the first 40 minutes of that 1 hour and 25 minutes. For the other project use the last 40 minutes of the session.

You already know that time cures most defects. Why not see if a challenge makes it mess up.

Now if you really wanted to turn this into a science project you would go back with your Locus.

Phil

Im sorry. Im just now beginning to look at this board since I convinced the Comm. College I teach a Survey Class at to purchase the PM2. What are these N and E differences relative to?
Is it the preliminary position or what?
And why can the PM2 obtain more sats than the Locus? Aren't a couple of these sat's broadcasting the WAAS corrections only?

NM,LS

NM,

The Locus is an 8 channel receiver.
The PM2 is a 10 channel + WAAS receiver.

That's the easy one.

JD will correct me if I'm wrong but here goes......

Receiver 1(R1) is on a known point.
Receiver 2(R2) is on a known point.
Receiver 3(R3) is on an unknown point.

Observation made. Software calcs postition of R3 :
case1) relative to R1 AND R2.
case2) relative to R1 only.
case3) relative to R2 only.

Finally these were included with other observations and the product of the ENTIRE network produced the adjusted coordinates of R3 at the end.

Jimbo

Modified By James Webb on 10/29/2001 at 5:00 PM

Thanks Jimbo,
So those are the actual processed coords. and its within 1' of 0N, 0E. Thats what was confusing me. JD must have assigned 0N,0E on his grid to a mapped point within a foot of the meas. point. Impressive results.

Question:
If the canopy had been too heavy, would one know that the solution was no good by observing the PM2 in the field?

NM,LS

Sorry NM.......

He just gave the decimal portion of the coord. rather than put out some 12 digit numbers. The decimal portion is all that was changing....2nd and 3rd decimal place.

Can't answer the last question.

Jimbo

Jimbo

Thanks. You answered exactly right. I was afraid the decimal thing might cause confusion, but like you said just didn't seem necessary to post all those million numbers too.

Phil,

Wish I had time to 'spearment right now. Barely had time to post what I thought were pretty impressive results from a real job situation last night. I considered doing my true "side by side/real time PM2-Locus" comparison on this project but didn't have time to set it up. We've done this a couple of times: set up a Locus unit with kinematic bar and a PM2 on the end of the bar. Set other Locus units with PM2 a couple of feet away in wide open clear areas. The Locus/PM2 on k-bar would have been a good evaluation of the situation under the canopy. Same canopy, same constellation, same solar conditions, same basic position. This is the procedure we used to find a bit of vertical difference mixing Locus and PM2. May not be totally scientific but seems to be somewhat reproducable.

J.D.

p.s. when viewing the raw data files for the receiver under the canopy they showed about a bazillion "loss of lock" and data gaps. I wish we could conventional into this point to verify the results, but I happen to trust them enough for the job at hand and just don't have the time.

Did ya see who's running the new TDS WAY Board ???!!!!!!!!!!(see top of general board)

Might wanna check in when ya get 30 sec. !!!!

Sounds like ya'r being hammered getting this job out. I know da feeling sometimes.

Good Luck,

Jimbo

J.D. If you have my numbers for the ProMark2 antenna please remember that I was just tinkering at my desk coming up with those parameters for Ashtech Solutions. I am hoping we are ready to hand out the "official" numbers soon and then we will see how well I did. If you got elevation variations using Locus and ProMark2 then you may get to blame me before all is said and done.

NM, The WAAS connection to the ProMark2 is only used in navigation mode. Here is a thought for those of you who do survey projects that are not tied to the NSRS (Sorry, National Spatial Reference System) Get coordinates for your control point in Navigation mode. You can set the thing to UTM and get it to squirt out numbers to the nearest meter. The coordinates are not accurate to the nearest meter but that is the fastest way to take advantage of the accuracy that WAAS adds to the navigation mode. Use the NGS Geodetic tool kit to convert those UTM coordinates to the coordinate system of your choice. You could even use Ashtech Solutions to get this done but why not go to the "official" source. Use that as the seed point for your GPS work on those projects where precise geodetic positions are not such a big deal. Then switch to survey mode and start your GPS session. Remember that you can use navigation mode between your static sessions. Just turn it on and go to navigation mode after your static session is over.

NM, In survey mode you have a sky plot screen that will let you see what SV's are on the job for you as well as letting you see a display of those signal to noise ratios. If you see those bars drop low it is often because some tree limb is now between you and the SV. You can nearly predict the cycle slips that will show up in the data processing.

JD, remember there are some tools in Ashtech Solutions to let you chop out some of those problems if they do end up making the solution blow up on you. You did the right thing by spending that extra time on that setup. I understand that work is more important than science projects. A guy has to eat.

Phil

Phil
Does Ashtech have an on line tutorial for basic GPS Survey procedures and/or processing data with the Solutions software. Each person in class sits at a PC terminal that I can take control of and an online tutorial would work great. I guess it would work the same if the system comes with a tutorial on a CD.
Thanks NM

Norm, It's a great idea and should go in the suggestion box. Would you send that in a letter? Truth is I find myself hitting that help file every time I turn around. This is one of the most helpful help files I have ever seen. You guys might be surprised how often tech support answers come right out of there.

So, should this tutorial CD be an extension of that help file or something different?

Have you looked at Practical GPS Surveying? That is a freebie from Ashtech in the manuals folder.

I'll have to hold suggestions or letters until I get a chance to view the help. Perhaps that's enough. We dont have the software yet. It should be in anytime.
Thanks NM

What software are you using to process your data...for these situations?

Ashtech Solutions 2.5