Measuring manhole inverts with JMate

Adam

Well-Known Member
5PLS
I wasn't scanning them but I did take shots on the pipe Id on each side of pipe to determine the width.
 

Adam

Well-Known Member
5PLS
@Javad gets a Blue Ribbon for best invert measuring device I've ever used.
No total Station I've seen can do this the way the JMate does. The offset camera/vertical action hasn't been done before and I see huge advantages.
15571802632671103399281.jpg
 

Adam

Well-Known Member
5PLS
I've measured many inverts in my career. Anyone who says they can measure them to the hundreths with a shit stick(pipe mic or not) (handheld laser or not)is full of it. Today I measured the most accurate inverts I ever have. Relative accuracy of a mm or two at most on elevation. Yes the inverts were recessed. I'm embarrassed to tell you folks what I measured with the shit stick a few weeks ago and thought it was good. It wasnt, matter a fact it put the shit flowing uphill. A tenth or two, sometimes it matters , sometimes it doesn't. JMate gets an A+ plus for this task.
 

Adam

Well-Known Member
5PLS
I haven't fully tested out the compensaters yet. You may be exactly right.
 

Joe Paulin

Well-Known Member
Are you shooting the top id and then subtracting the id to get flowline? Will the JMate shoot through the liquid or give a reading to the surface of the liquid? The handheld laser distance measurers that I have used wont shoot through the liquid.
 

Joe Paulin

Well-Known Member
Also not to mention you can get direct survey shots on all the features inside instead of doing data sheets for each manhole. Very nice.
 

Adam

Well-Known Member
5PLS
Are you shooting the top id and then subtracting the id to get flowline? Will the JMate shoot through the liquid or give a reading to the surface of the liquid? The handheld laser distance measurers that I have used wont shoot through the liquid.
Curiosity got the better of me so I performed a quick "bucket" test.

Here are the results starting with an empty bucket. Water depths listed in decimal feet. As you see it is shooting thru the water but the measurement is distorted slightly as the bucket fills up. I would say for your normal sewer lines with .1 to or .2 of depth it is okay to use the readings. Anything over that I may adjust the measurement based on what I've found below. It's fairly linear until the jump from .5 to .8. Now I am curious about deeper water. Never did it give a return to the top of the water.

C31,-1.011,-0.052,-6.287,Empty bucket
C32,-1.011,-0.052,-6.287,Empty bucket
C33,-1.015,-0.050,-6.314,.1
C34,-1.019,-0.048,-6.341,.2
C35,-1.024,-0.046,-6.376,.3
C36,-1.028,-0.045,-6.405,.4
C37,-1.034,-0.043,-6.440,.5
C38,-1.033,-0.043,-6.431,.8 Full bucket
C39,-1.011,-0.051,-6.288,Empty bucket

KIMG0705.JPG
 
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Adam

Well-Known Member
5PLS
I wanted to see if distance to the water had any effect so I ran the test again from a little higher up. The results indicate that the values change based on distance from the surface. I see the water slows the return while traveling thru the water. Because of this the speed of the laser exiting the water is less than before it hits the water so the distance down to the water does matter. The further from the water the larger the descrepancy. It probably could be compensated for somehow.

C41,0.137,0.318,-9.694,Empty bucket
C42,0.139,0.317,-9.725,.1 (.031) before was .027
C43,0.141,0.317,-9.789,.3 (.095) before was .089
C44,0.144,0.317,-9.868,.5 (.174) before was .153
C45,0.148,0.317,-9.973,Full bucket .8 (.279) before was .143
C46,0.137,0.317,-9.694,Empty bucket
KIMG0708.JPG
 

Jim Frame

Well-Known Member
I see the water slows the return while traveling thru the water. Because of this the speed of the laser exiting the water is less than before it hits the water so the distance down to the water does matter.
I'm pretty sure that's not the way light works -- I think it's speed is constant through a given medium, no matter what medium it traveled through previously. But it's an interesting question, and I'm going to pose it to my son the physics major.
 
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