Carrying elevations through a traverse...
I posted about this project before, but here are some results pertinent to the current discussion (sort of).
We ran a traverse up the middle of a small river. Most stations were in the water, not marked.
We put GPS on the same setup for some of the stations to provide control as we went along. The traverse stations are green, GPS occupied stations red: 
Because of a flash flood one day, the main traverse got broken near the upper (east) end one day, so it is actually two traverses. We were traversing along, heard a roar, and a wall of water came down the river and caused us to have to immediately pick up the setups. We used forced centering, but of course had to set ground points on shore at the end of each day and re-setup the next day, which broke the chain of forced centering. No effort was made to keep sights short, lengths ranged from 30 feet up to 1600 feet. The main traverse is 18 miles long, and there were 102 stations in the main traverse.
Anyway, here is a plot that shows the misclosure between the traverse elevations and the GPS positions (post processed fast static). The blue line is constrained at one end, the red line is constrained at each end (i.e. two fixed elevations).
So, there was a definite trend in one direction, but it was fairly consistent, so by fixing each end vertically, all of the GPS points agreed to better than 0.2 feet. When I fixed all of the GPS points, the vertical confidence regions (95%) were pretty good (this graph shows to the end of traverse 2, a total of 22 miles:
There was no way we could have leveled to any of these points, they were in a steep valley with very limited road access, and most were in the river, not marked. But, the end results were plenty accurate enough for what they wanted (90 stream sections spaced about 1200 feet apart).
TRIG LEVELS/TS Jesse Kozlowski,PLS
Ive read the Koz article, and also another couple as well on the subject of trig levels. For me, this just wasnt an attractive way to go for the few times I need tight elevs.
As for what I am finding on laser levels, they are accurate to 1/16-+ in 100 feet. Not that great.
TRIG LEVELS/TS Jesse Kozlowski,PLS
We run a lot of precise levels (Dini 12, invar rods, etc), but there are plenty of times we need an elevation on an intake tower roof, or on a pier, or at the top and toe of a dam. In these cases, we use trigs, which I believe gives us millimeter accuracy. You just need to know a few tricks and you can achieve second order results with care, third order pretty easily.
Carrying elevations through a traverse...
Cool! Thanks for sharing...
Jeeesh, do I have to draw a profile?
end of hose 6' above ground
350' along ground at 15%
other end of hose 60 feet above ground (equal to first end at 6')
Carrying elevations through a traverse...
It was one of those jobs that seemed like a pain when it was going on, but looking back it was a lot of fun. I would gladly do another one like that (in the summer!).
The drawbacks were the lack of access, so we had to travel far each day to get in and out, and the copperheads:bored:
Carrying elevations through a traverse...
Cool project and data!! but it sure made me clench up when I saw that robot set up in the stream! yikes.
> Andy J: What have you found the max distances you can stretch your laser level shots?
>
I usually keep the laser level shots less than 150-200 feet. I have done a peg test with it and it does a fine job. Just have to keep track of the batteries, when they start to go bad, the speed slows and I assume the accuracy.
My Geodimeter is a Bergstrand 650 1 second instrument. I have checked shots to my 360 prism with a level out to about 600 feet with consistency. I think it would be even better with the other prism, but rarely need to shoot anything that far anyway.
Check out this presentation of the Kozlowski Article. It was made a lot clearer with the pictures
The illustrations help for sure. But to me this application would make sense for sites with lots of change in elevation and not necessarily those with with only relatively slight undulation. Maybe Im just lazy.
> Or enlist the wife to help run loops.
:good:
I had the wife out on a geotracker job a couple of months ago to run levels. She keeps asking when she can quit her day job to come work with me full-time.
Mack,
A couple of years ago, on a National Guard Readiness Center, the general contractor's surveyor gave me 8 control points around the building, and he labeled each lath with an elevation.
"When are you going to give me a benchmark?" I asked.
"Just use the elevations on the lath," he responded.
I'm thinking to myself, "Bull****! The only way to get good elevations is with a level loop." So I ran a loop myself, and damn if they weren't all within half a hundredth. That day I gained a new respect for the Trimble S6.
As for laser levels, I don't trust them. Every problem I've ever had with elevations was from using a laser level. I use them all the time for footings, but for anchor bolts and critical elevations, the autolevel is still the best choice.
So, I'd say trig that loop or grab a warm body. Or the thumb-release tripod might be do-able.
Oh, and I'd love to see Tom Adams choreograph that 3-man dance. With the right music, such a You-Tube could go viral!
Dave
Carrying elevations through a traverse...
I thought the same thing. Pucker factor would have been pretty high for me...
To secure the level rod, you should try using two bi-pods.
I use a Topcon DL-502 digital level for solo level runs. I'm connecting a Parani SD1000 Bluetooth/RS232 Serial Adapter to the DL-502 and use a Topcon Tesla with Magnet via longrange bluetooth.
I can set up the Digital Level, point it to my backsight.
Walk over there with rod, take the reading and record. Then walk past the digital level, turn to the foresight walk over and take reading.
Works for me, and far more accurate than the laser levels.
If I can find office rat, I can have them turn and point the DL-502, and they help carry things. But I still use the long range bluetooth and data collector.
Lee Green
> Jeeesh, do I have to draw a profile?
>
> end of hose 6' above ground
> 350' along ground at 15%
> other end of hose 60 feet above ground (equal to first end at 6')
If both ends of the hose are at the same elevation (real elevation, not height) from ground, there is an equal amount of water up as down, and what is more, the air presses the same on each end (more or less).
The hose supports the pressure of the water, not the ground. The ground supports the hose.
If you have a hose, the water level will equalize, either by running out, or by finding level. It doesn't matter how high you pull one end up a 2:1 slope while pulling the other vertically up a ladder.
Carrying elevations through a traverse...
Just looking at those pics makes me hate this winter a little more, looks like fun.
It's more stuff to carry, but if it's windy, lead shot bags ('ankle weights' to scuba divers) are handy to drape over the foot of the bipod legs. Similarly, if it's a hollow rod/staff, a load of cuttings of rebar inside add mass at the base.
Aloha all, thank you so much for these wonderful educational posts! :good: :good: :good:
Trimble access has a 3rd party add on program that does the trig leveling routine , I saw it on a dealers demo tsc3 and downloaded the PDF , it looks quite good.
Here is the link to it on trembles site
http://apps.trimbleaccess.com/SETTOP/Level_Me
And to the developers site
I don't understand what's so complicated. You read the back rodman and call him off. YOu can immediately turn and read the front-rod without waiting for someone to walk forward and find a spot to turn. That how first-order levels are traditionally run.
I get that your teasing me, but I don't know why you think it's some kind of complicated cluster-$$. It's simply more efficient as I see it.
