I was thinking today about how common consumer electronic rangefinders are. I wonder if someone could do a little reverse engineering on one and turn its output into an electrical signal that could be connected to something like an arduino or other micro processor. The microprocessor could in turn convert the output to an audio callout that could have standard callouts, or could even be programmed and recorded by the end user if desired. It would provide an extra level of situational awareness under normal circumstances and give the pilot a few seconds of warning if the ground was sneaking up. For pilots landing on unsurveyed sites it would be possible to have an accurate AGL altitude for the last couple hundred feet of the approach.

I could probably figure this out if I didn't have anything else to do, but that's not the case unfortunately. It would be even better if someone else were to figure it out and make one for me at a discount. Surely there is someone ambitious hanging around here...

I can think of ways to do it, but-- I personally don't find precision altitude that useful for daytime VFR. Even landing short nasty rough stuff is a purely visual seat of the pants operation. Maybe there are uses I'm not smart enough to think of...

Laser rangefinders sure are handy for lateral distance measuring though while on the ground.

why not just use it as a rangefinder, just vertical?

It would help over glassy water when you're about to "hydro planing the wheels"

One of the requirements for flying NVG's is a radar altimeter...wonder if this would qualify(although it uses laser rather than radio waves)...hmmmm

I do a lot of long-range hunting so I have become pretty au fait with high-end publicly available rangefinders.
They do have a few weaknesses which would need to be considered.
They are not great with any precipitation in the air (typically under-estimate distance, sometimes drastically), their useful range is effected by daylight conditions and obviously the surface, and you need them to be pretty still and steady to get readings consistently.

To be honest, I can't think of a practical use for backcountry flying, except maybe hydroplaning the wheels.
But is certainly is a creative idea. Build one and see if it sells?

Pretty straightforward with infrared or ultrasound proximity sensors. Everything you need is available at sparkfun, including the arduino breakout boards:

IR with 5 feet resolution:
https://www.sparkfun.com/products/8958

US with 25 ft resolution - at cm increments of accuracy.
https://www.sparkfun.com/products/9495

Above 25ft your GPS will be more accurate - presuming you have high resolution terrain information - not sure where foreflight gets theres - they get everything else from the FAA - perhaps that too can be downloaded.

Lots of info on building/hacking laser rangefinders here:
https://forum.sparkfun.com/viewtopic.php?f=14&t=8781#p38325

I know WIngX has a high-res terrain database that calculates AGL all the time, assuming Foreflight probably does the same thing. Since it is GPS based it should be accurate to some number of feet which is good enough. Seems pretty darn accurate and great for figuring out what altitude you need to clear that next pass.

Laser rangefinders are pretty messy. They barely work when you move them across the ground...they need data filtering to tease out the noise, with variable results, and as mentioned before, humidity and precipitation are a significant factors to accuracy.

Microwave or radar is much better all the way around. It isn't even uber expensive, but more than hacking a LRF. Even better, a simple point cloud file to determine your AGL based on GPS location. It may sound odd to hear, but the folks who care about this stuff a lot are moving to that and away from laser rangefinders.

Keep in mind that even low power classes of lasers are still not allowed on planes...the FAA has given a lot of input on this.Unless you are indemnified by public use, you have to disable your LRF when in flight. Even silly class II lasers.

BUT- besides all that stuff, why would a LRF be useful for VFR?

Searey has partnered with this guy for his device. It should work for anything.

http://youtu.be/ZcBYgEG7zX8

That's a pretty neat idea! Good for that guy!

Nice! I don't have any particular need for an agl presentation, but my original question was as much a thought experiment as anything else. Thanks for the insights about the limits of laser rangefinders!