This sounds like basic surveying.  Distance measurment using lasers is
likely your best bet since they will go that far and return a usable
signal, but also because you can point them very accurately and know
you're pointing at what you'd like to measure.

-Adam

On 2/28/06, Tony Harris <kg4wfx@yahoo.com> wrote:
> Hi all,
>
> I'm tinkering with an idea, but I think it is beyond me - I'm not sure tho.
> Basically, it's a height at a given distance determination.
>
> I was thinking of using 2 sensors one angled down and one angled up, using
> the angle between them, and the distance calculated from the sensors to
> determine the height.
>
> This worked out pretty good until I found that only short range sensors are
> cheap :)  I'd like to figure out something that would read say a hundred
> feet ahead.  The idea would be to measure the height from an overhang or
> bridge or opening to ground from a distance.
>
> I was then thinking of some sort of camera system to capture an image, say 2
> per second, but then came the problem of determining automatically what is
> above and where "ground level" is to that above area.
>
>
> So, if you can imagine - in my rather lame ascii art....
>
> Top of overhang
> --------------
>         \
>          |
>          | Heigth to calculate
>          |
>          |----------------------------------------------------------------------
>  > Point of origin, exact height (give or take) by combination
>          |                                     < --  Distance, 25 - 100
> feet -->                       data entry or perhaps gps (got that idea from
> looking at gps data
>          |
> from a remote control helicopter video feed project on the net)
>         /
> ----------------
> Ground
>
> I'm sure you can see why the triangle option is very tempting, the problem
> is distance, doing it without lasers (would suck to have someone walk in
> front of my new toy and get blinded and sue me because I was experimenting.)
>
> That's why I was thinking images, but I don't even know where I would start
> research on something like this.
>
> any suggestions welcome.  Just something I was toying around with and knew
> there had to be a way to do it, but was stumped due to distance...
>
> -Tony
>
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