for years we have been measuring inverts of catchbasins, manholes etc for underground services here in canada. always just measured using a tape measure or level rod etc. but more often than not there is an offset pipe invert from the manhole rim that makes it rather hard to measure acurately has anyone seen a special prism pole or built your own device for measuring these offset inverts? ideally i would like to tie them in directly with the gps via prism pole to eliminate error from field crew to drafting etc.
here is an example of what i mean
Thanks
Here's link to one that works on a fiberglass level rod.
We have a Leica Disto that does slope and vertical distances so you can point it on an angle from the lip of a manhole to the invert of a pipe and it will give you a vertical distance.
I have a pipe mic that Stephen provided a link to. It has made my invert information much more accurate, and easier to obtain.
We actually hop down into Storm Water Manholes (staff are Confined Space trained) to get a very accurate Invert levels for that.
For waste water (sewer) we use something similar to ones already posted, but built in house.
Go to the hardware store and for about $10 you get a plumbers weighted protractor that will give you the slope of the slanted rod down in the invert. A minute or so with your calculator and you have a vertical distance. It is easy to carry around and it works!
Ken
One advantage of the PipeMic is the way you can accurately get pipe sizes.
> One advantage of the PipeMic is the way you can accurately get pipe sizes.
True, but you can only read the rod from one side! I have one, it sits collecting dust as it is a PITA to use sometimes. Usually just measure the c/l invert
-JD-
> for years we have been measuring inverts of catchbasins, manholes etc for underground services here in canada. always just measured using a tape measure or level rod etc. but more often than not there is an offset pipe invert from the manhole rim that makes it rather hard to measure acurately has anyone seen a special prism pole or built your own device for measuring these offset inverts? ideally i would like to tie them in directly with the gps via prism pole to eliminate error from field crew to drafting etc.
For the most accurate measurements, we enter the manhole. This is kept to a minimum due to safety concerns. We do this with all new construction that we are doing an as-built on.
For location of existing structures, we take into account the situation and the needed accuracy. Most manholes in our area are 48" diameter. This means that measuring with a fiberglass level rod from the invert to the rim at the center of the structure results in a right triangle with the measured distance being the "c", and "b" being 2.0'. Then the vertical distance is calculated. In practice, when we have checked this, if done carefully, this results in repeatable measurements accurate to within +/-0.05' compared with entering the manhole. Our experience is that entering the manhole results in repeatable measurements of +/-0.01', with good care and procedures.
In many cases, the center-line of the channel of the manhole is used, depending on the expected use. Including metadata with measurements allows for the project surveyor or engineer to appropriately use the data.