We are doing topo of an area that needs to be repaired (landslide). There are some issues between the feds (C of E), who have a large project that has access blocked by the landslide and the local municipality (who owns the road that collapsed)
We located the sanitary lines through the site, 13 manholes, no problem (does this look confusing?):
But the storm drains (inlets) are quite confusing. The only storm manhole is one of the four in the intersection above. All of the curb inlets and drop inlets appear to have only one pipe exiting.
So, I went to the local municipal offices (small town, 1.6M annual budget) to ask for maps of the storm drains. They don't have any (?). But, they said they would send their guys out to mark the lines. They just connected the dots between inlets, like they are all flowing one into another. Notice the double headed arrow to indicate flow both ways?????
Well, I have pretty much figured out that there must be a pipe under the road (no manholes or other access, and all of these have to flow into that pipe. But you would think they would know that?
Then, when I was surveying a stream tunnel that goes under the road, which is under the railroad, I found a pipe coming in, about 8' up the wall:
Here is how we shot that invert, using a dual prism rod:
I had never used that method before, but recently we have had two projects that really needed it, works great.
i do not know this 'dual prism rod' you speak of. please explain.
> i do not know this 'dual prism rod' you speak of. please explain.
I've seen these before, you locate the 2 prisms and the software calculates the position of the tip of the rod, based on their location and the distance to the tip.
Pretty slick...:-)
Radar
You have two prisms on the rod, and you have two HI's. You can hold the rod at any angle. The TSC2 Survey Controller has a routine to shoot this, and it stores the coordinate/elevation of the tip of the rod (i.e. the "hidden" point). Shawn Billings wrote a very good articale about it in American Surveyor:
A couple of weeks ago we had to determine the verticality of some metal guide plates on a couple of piers on a dam. Seems they just installed a new gate, and it was coming off the track (the tracks were installed in 1937) at the bottom. We were able to scan the downstream plates using a GX scanner and setting up on a sill (the concrete base the gate rests on). The only way to access the upstream plate was to ride a dam gate (harnessed off, of course), stopping every foot to shoot the face of the plate using the dual prism rod. 40°, wind blowing about 35 knots, but we got it done. Then, I realized that I had incorrectly entered one of the prism offsets into the data collector (-30 instead of 0). Panic. The dc file only contains the reduced observation. And we were looking for millimeters. I figured out that the raw shots to each prism (A and B) are in the job file (which isn't ascii), and by creating a jxl file I was able to get what I needed, then setup a spreadsheet to re-compute all of the 115 points using the correct offset.
Here is what the results looked like, a plot of distance between the plates versus elevation:
Looks like they got a problem.
Nice pictures,
I never used the double prism rod
you set a very good example
Chr.
I guess it could be done without a data collector routine. I manually processed it all, using the formulas that Shawn gave, but the shots were labeled "E080-prism A" and "E080-prism B" (where E080 is the point number) in the jxl file, so it was pretty easy to set it up.
Here is what a shot looked like in the html file:
I had to wrote a program to parse that html file and extract all of the observations I needed.
The Trimble Survey controller software has the routine (called a Dual Prism Offset), I would be interested to know which others do as well.
Simple way is to just shoot the 2 prisms, then in the office project the 3d line between those 2 3d points the distance from the bottom prism to the rod tip. Assuming the prisms have the same offset. Have to hold the rod steady to be accurate.
Topsurv has this routine also.
This is available in Surveyors' Tool Kit. It works very well.
As does Leica.
The manholes with the circles on them are electric aren't they. No worry about opening those.