Absolute measurement devices

[Yovav]

Hello
Are there absolute measurement devices? Device that can measure absolute height of a point?
for example lets say I need to measure two point when each point is on different location, but what I need to know is the differential between the two points although I have different ground height for each point, and the ground height is unknown (in comparison to sea level height)

p.s. (for moderator)
I asked the same Q in a different format before, hope it's not a problem, if so, let me know

[BillTodd]

What scale?

GPS will give you an altitude accurate to a few metres (perhaps better if averaged)

A simple water tube manometer could be better than a millimetre (if the tube is not too long)

[Geof]

What is the distance separating the points and the difference in height?

For distances less than 100ft and heights that differ by less than 10ft probably a plastic tube is the simplest.

If you have lots and lots of money you can get GPS based instruments that give heights and distances in the millimetre range; this are used to detect ground motion around volcanoes and to monitor tectonic movement.

Or you can pick up some surveying equipment and triangulate it.

[Yovav]

The scale is in microns, so GPS won't be god, the water tube on the other hand sound like it has potential, I'll do some internet search, and maybe that's the answer

[Yovav]

Originally Posted by Geof What is the distance separating the points and the difference in height? For distances less than 100ft and heights that differ by less than 10ft probably a plastic tube is the simplest. If you have lots and lots of money you can get GPS based instruments that give heights and distances in the millimetre range; this are used to detect ground motion around volcanoes and to monitor tectonic movement. Or you can pick up some surveying equipment and triangulate it.

The distance is less the 10m (32,81 ft) and the differ is less the a millimeter,
Triangulation sounds very interesting, maybe it's possible to triangulate the right equipment to get a real good accuracy, I will search if someone has done it before

[lerman]

I recently saw a gadget that will track an eyeball sized retroreflector and give its position within three thousandths of an inch in a 40 foot cube. (I believe I got those numbers right.)

Do you have a few hundred thousand spare dollars in your budget?

What precision are you looking for?

Ken

[Yovav]

Originally Posted by lerman I recently saw a gadget that will track an eyeball sized retroreflector and give its position within three thousandths of an inch in a 40 foot cube. (I believe I got those numbers right.) Do you have a few hundred thousand spare dollars in your budget? What precision are you looking for? Ken

No, I don't have a few hundred thousand to spare
I have only 2K$ in the budget for that specific assignment, but I don't need to buy the device only to use it.
Where did you read about it?
It sounds interesting even if a bit unpractical

[Geof]

A thought just entered my mind. Fixtures for assembling small aircraft wings are optically aligned and calibrated to locate the 'hard points'; you need to find someone involved in this type of thing.

[keebler303]

I went to a presentation on this stuff a couple years ago. Seemed pretty darn cool.

http://us.metris.com/large_volume_me...y/laser_radar/

102 micron accuracy at 10m distance.
But as stated previously, LOTS more than $2k.

I think the tube method would work, you just need to devise a clever way to measure the water height at each end of the tube. Something like a graduated cylinder which connects to the tube.

Matt

[Yovav]

Originally Posted by keebler303 I went to a presentation on this stuff a couple years ago. Seemed pretty darn cool. http://us.metris.com/large_volume_me...y/laser_radar/ 102 micron accuracy at 10m distance. But as stated previously, LOTS more than $2k. I think the tube method would work, you just need to devise a clever way to measure the water height at each end of the tube. Something like a graduated cylinder which connects to the tube. Matt

This seems like the best solution, but look really expensive, I guess I will need to do it old school and build an aluminum frame for reference (time consuming but cheap).
Thanks for all you ideas; it was very kind of you to help
Yovav

[lerman]

Your aluminum frame will be dependent on having a precise level. How good is your level?

Ken

[BillTodd]

Your need for a measurement in microns and the words 'aluminium frame' don't sit well together

Ken, Is it wise to publish your address on-line?