Laser range finder vs. IR range finder

So my project objective is to measure the inner diameters of cylinders (50"~ diameters). What would be a better option? Laser range finder or IR range finder? I need something with high accuracy and something that would be able to give me real time results.

Maybe Lidar? http://www.pulsedlight3d.com/ http://pulsedlight3d.net/assets.pl3d/LIDAR-Lite-Data-Sheet.pdf Accuracy: +/- 0.025m

1m = 39 inches, so 0.025m = 0.975" Doesn't seem that good if I converted that correctly.

http://www.parallax.com/product/28015 Comparable to 2cm (0.78") range.

Maybe one of these https://www.mysick.com/ecat.aspx?go=FinderSearch&Cat=Row&At=Fa&Cult=English&FamilyID=380&Category=Produktfinder&Selections=77544 with one wall fixed, can measure the other wall down to 1um, if it's 1cm to 2cm away, and less accurately (6um) if there will be more variation.

Other possibilities https://www.google.com/#q=high+precision+distance+measurement

Thanks for the resources CrossRoads!

I have a tape measure that one side is scaled to measure diameters. It's normally used to wrap around OD's. Every pi inches is marked as 1". If it went around a large ID it would work.

There might be some way to adopt what that does or turn what it does around a bit.

Like suppose the inside is dark and you have something that makes a bright light at an exact but not large angle. From the center of the diameter to a side or from one side to the other, the width it would light up could by formula tell you the diameter closely and the device could perform the calculation if not the measurement though for far less cost and no brain chip you could get the answer off a printed card.

look at keyence how they do it. if the pipes are all around 50" use a stick of 49" and a laser to send a beam. if the beam is rflected you can measur it with a photo position sensing device.

a cheaper way use a laser diode to send a beam , use a servo to rotate a mirror until the beam is targetted on a receiver. working with triangulation. you can solve the distance

I believe the actual answer would be laser interferometry using a tunable laser.

Accuracy extreme - to within nanometres - but expensive.

Clearly the topic has nothing to do with Arduinox.