Sensing absolute height

I have a platform that's attached to a rolling chassis by linear actuators. As the chaiis moves the wheels be be on uneven terrain but i need the deck to run up and down to maintain a fixed high.

Right now i have a rotating laser on a tripod sending signals to a laser signal receiver to give me absolute level now. The receiver drives the actuator up and down to keep itself at it's specified height level.

The laser set is big money and i would like to think of a way to do this with the arduino if possible. If i do this i can also customize some features and perhaps drive a display to show me relevant information. Can anyone think of a good way to find an absolute height?

*note - ground height will change so i cannot just sense the height from the earth

I am not against keeping the tripod rotating laser and attempting to just buy the receiver side as that end is the majority of the money. Think this may be do-able? I am not sure what type of receiver is would use for this.... would those rotators use IR? Just looking for some general ideas...... and i am sure i left out some major detail... so feel free to ask and i will try to paint as good of a picture as i can.

Does this need to be done continually while the chassis is moving, or only to set the height (and level?) after it has been parked?

Presumably you have a point somewhere that you will be using as a height reference. How far away from this do you need to get, and what sort of tolerance do you have on the height?

Any practical constraints, for example can you run a hose out to it and use a water level?

The chassis will be rolling and there will be lots of vibration (engine running and blades turning). Likely running a sort of grid pattern over a patch of ground.

Distance constraint will likely be up to 50ft or so. Height needs to be as close as possible to the set "zero reference". perhaps +/- .25"

water level sound like a very interesting idea..... will have to think about this some..... it would have to be off of the ground so it doesn't get rolled over and chopped by blades though.

A water level won't work well while it's moving.

I wondered about using a visial beacon and have the rover work out the relative elevation of the beacon, but you need to know the orientation of the rover and then do some pretty precise optical sensing to get that working.

I wonder if there's another approach. I remember reading that it's possible to get very sensitive pressure sensors that can give you an absolute altitude to within a few centimeters. If you used a vertical accelerometer to detect short term displacement and a pressure sensor to give you a baseline to compensate for integration errors from the accelerometer, I think you may be able to get something working. I don't think it'll be easy to get the sort of accuracy you're talking about, but it might be possible if you get something working and then gradually refine it.

Seems like you have two different requirements: one is to heep a moving platform level with some other reference point, and the other requirement to keep something like a mowing deck at a specific height above another surface. You may need to address those requirements individually.

Do you guys think something like this or this would work?

I see some threads on using this to get a height off of a weather balloon or a kite....

What kind of resolution could i expect (assuming i use an external chip to get full resolution form the sensor) using these sensors?

zoomkat: one is to heep a moving platform level with some other reference point

Already being addressed using a 5DOF from spark fun. This will be the short term solution for now still using the rotating laser assembly.

zoomkat: the other requirement to keep something like a mowing deck at a specific height above another surface

This is the one i am really questioning because it would be what is needed to replace the expensive survey unit.

I just did a google "rotating laser detector" and found this.

Don't know what you would define as expensive. Sounds like it outputs different tones for homing in. The hard part would be to keep it aiming at the rotating laser level as you move around. Compass driven perhaps.

I'm working on a project exactly equal to this. Problem is; "getting a data" from this laser receiver and also process it via Arduino.