most accurate way to measure...

[GT]

Recently, I needed to measure a distance in the garden, of roughly 30 feet, which I know can be done adequately with a simple tape measure, to withing an inch or so.

But then I got to thinking....purely out of curiosity, what would be the MOST accurate way to measure distances of say 20 to 50 feet, outside, on uneven land. Or for that matter, between any two points !

I expect to hear all about sonic measuring devices, tape measures pulled very tight etc. etc., but what i'm really trying to discover is who can come up with the MOST ACCURATE, regardless of cost.

Then, the MOST ACCURATE, at the least cost.

Also, i'm curious as to just how good the measuring devices currently on offer really are.

I know there's not a lot of practicality in this exercise, but I thought it might get a few brains ticking. GT

[The Natural Philosopher]

A rangefinder on parallax is pretty good, as is a ladar type rangefinder...but the old fashioned ways are the best. Theodolite, chain and triangulation :D

[dennis]

Over that distance: a tape measure in both cases. One by putting it through a ridged tube to keep it straight.

Unless you are talking about building a temperature controlled room and using an interferometer to measure differences of a few wavelengths of light that is.

[Owain]

Not sure about accuracy but:

Put a clearly visible marker of a known length in the centre of the plot.

Send up a camera on a small helium baloon, above the centre of the plot. Take aerial photo.

Scale the photo according to the visible marker.

Having the photo and marker based on the centre of the plot should even out perspective errors?

Owain

[Malcolm Stewart]

With my Leica Disto*, I'd have no problem measuring your slant distances to

2mm, or may be 1mm. If you're interested in longer distances, put your query to a surveying group where they know about refraction corrections, earth's curvature etc. With my Leica Disto mounted on my Wild T2 theodolite (to get the laser beam level to within a few seconds, which is far better than you'll get with the laser levels etc. from B&Q), I'd have no problem measuring your true horizontal distances to 2mm, or may be 1mm. Or with suitable precautions, you could use a properly tensioned and temperature corrected standard tape measure or chain.

• It's one of the first, so whilst valuable to me, it now has very little resale value.