What about the recent work done on the Shuttle, where there was a 
"laser-camera" used to inspect the ceramic tiles once the shuttle was in 
orbit.

If I am not mistaken, the process used parallel laser beams to create a 
reference on the tiles, and then the reflected light could be used to 
read the reference beams.

The observed distance between the reference marks would be inversely 
proportional to the distance of the reflection from the observer.

There was an article recently where it is now being used in crime scenes....

Here...:
http://science.slashdot.org/article.pl?sid=06/03/01/1912255

Rolf

Howard Winter wrote:
> Tony,
>
> On Tue, 28 Feb 2006 20:50:39 -0600, Tony Harris 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.
>>     
>
> Basic triangulation - measure the horizontal distance, and the angle from horizontal to the top.  I did it 
> once to measure the height of a tree...  of course it may be that the thing you're measuring doesn't have 
> anything directly below it, in which case you have to measure the slant distance.
>  
>   
>> 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 think Polaroid do ultrasonic sensors that go up to 30m, but laser would be much more reliable.  Not sure of 
> the costs, though.
>  
>   
>> 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.
>>     
>
> I'm not sure what your camera would tell you, or why you want more than one picture? 
>  
>   
>> 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.)
>>     
>
> Surveying lasers aren't dangerous to eyesight - they wouldn't be allowed otherwise!  Imagine roadside 
> surveying blinding (even temporarily) a passing driver... I think they use Infra Red so you don't even see 
> them.
>  
>   
>> That's why I was thinking images, but I don't even know where I would start 
>> research on something like this.
>>     
>
> You need to measure a distance - there really is no other way unless you know this, otherwise a 10' height at 
> 100' looks the same as a 20' height at 200', so anything purely optical with no distance measurement won't 
> work.
>
> Cheers,
>
>
> Howard Winter
> St.Albans, England
>
>
>   


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