torrik
Posts: 1
Joined: Mon Aug 20, 2018 4:08 pm

measure height elevation

Mon Aug 20, 2018 4:16 pm

Hi,

Is this possible to measure height elevation with a high accuracy with a RPi ?
I'm not looking for a pressure sensor that wouldn't provide sufficient accuracy. I want to be able to measure an elevation in the order of 1 or 2 cm.
What interests me is the relative height from point A to point B not the altitude

how do we get there?
Thanks for your help :)

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thagrol
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Re: measure height elevation

Mon Aug 20, 2018 6:07 pm

What sort of distances are you looking to measeure? And will you have a line of sight between points A and B?

For short distances with an unobstructed sight line you could use an ultra sound or laser based distamce sensor. Not sure what you'd use for long distances and/or without a clear sight line though.
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DougieLawson
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Re: measure height elevation

Mon Aug 20, 2018 6:23 pm

What sensor are you planning to use? GPS? Barometric?
Do you have datum elevation near to you like an airfield, airport or a hill with a trig point?
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jbeale
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Re: measure height elevation

Mon Aug 20, 2018 6:43 pm

There are pressure sensors that do have a few cm height resolution, for example, Honeywell makes this differential pressure sensor:
https://www.digikey.com/product-detail/ ... ND/3935154

its claimed *accuracy* is 0.25% full scale of 2.5 mbar, meaning 6.25 microbar or 625 mPa. At sea level & 15 C, that pressure change would be caused by a 5 cm elevation change. The resolution might be considerably better, depending on how long you wait to average the noise in readings.

Of course, a pressure sensor used as an altimeter is obviously affected by the weather- ambient barometric pressure is always changing, plus in practice there is always noise from wind, doors opening/closing, etc. which affects pressure readings at the few-cm level of sensitivity.

It is difficult to get cm-level height resolution from consumer-level GPS. For what it's worth, there are now $30 laser time-of-flight distance meters that have millimeter resolution over many 10s of meters. I have a Suaoki S9 and it does work as described. https://www.amazon.com/gp/product/B018FWF7X4

hippy
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Re: measure height elevation

Mon Aug 20, 2018 6:55 pm

torrik wrote:
Mon Aug 20, 2018 4:16 pm
I want to be able to measure an elevation in the order of 1 or 2 cm.
Are you saying the distance between one height and the other will be 1-2cm, or greater than that and you want to measure that to an accuracy of 1-2cm ?

W. H. Heydt
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Re: measure height elevation

Mon Aug 20, 2018 11:37 pm

torrik wrote:
Mon Aug 20, 2018 4:16 pm
Hi,

Is this possible to measure height elevation with a high accuracy with a RPi ?
I'm not looking for a pressure sensor that wouldn't provide sufficient accuracy. I want to be able to measure an elevation in the order of 1 or 2 cm.
What interests me is the relative height from point A to point B not the altitude

how do we get there?
Thanks for your help :)
If I wanted to measure a height difference of that magnitude, I'd pull the 6 inch steel scale out of my pocket and do it directly.

As a practical matter, I would suggest reading up on the difference between "accuracy" and "precision".

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