OT: Re: Looking For Geodetic Python Software

[Tim Daneliuk]

Rocco Moretti wrote:

> Tim Daneliuk wrote:
> 
>> Diez B. Roggisch wrote:
>>
>>> Tim Daneliuk wrote:
>>>
>>>> Casey Hawthorne wrote:
>>>>
>>>>>
>>>>> Do your planes fly over the earth's surface or through the ground?
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Why do you presume this has anything to do with airplanes?
>>>>
>>>
>>> That was supposed to be a funny remark regarding that  your 
>>> "straight-line-distance" makes no sense at all - because that would 
>>> mean that you'd have to go underground. So it has no 
>>> real-world-application - unless you actually have underground-planes ;)
>>>
>>> Diez
>>
>>
>>
>> Huh?   When traversing along the surface of the earth, it's curvature
>> is relevant in computing total distance.  An airplane flies more-or-less
>> in a straight line above that curvature.  For sufficiently long airplane
>> routes (where the ascent/descent distance is trivial compared to the
>> overall horizontal distance traversed), a straight line path shorter
>> than the over-earth path is possible.   That's why I specified the
>> desire to compute both path lengths.  Where's the humor?
> 
> 
> If you re-read what you wrote you'll see the phrase "straight line 
> flying distance.":
> 
>  > 1) Given the latitude/longitude of two locations, compute the distance
>  >    between them.  "Distance" in this case would be either the
>  > straight-line
>  >    flying distance, or the actual over-ground distance that accounts
>  > for the earth's curvature.
> 
> Casey was pointing out that, due to the convex curvature of the Earth, a 
> "straight line" between, say, Hong Kong and New York would happen to 
> pass several miles below the surface of California. For an extreme 
> example, a Euclidean straight line from the North pole to the south pole 
> would pass through the center of the earth. Note that you've attached 
> "Flying distance" to the phrase "Straight line" - Hollywood not 
> withstanding, there isn't a machine able to "fly" through the center of 
> the earth. The fact that it might be an unintentional error only adds to 
> the humor. (c.f Freudian Slips)

Yikes! And I thought I was being clear.  Sigh ... back to English 101
for moi.

> 
> Given the relative thinness of the atmosphere (~10-20 km) in comparison 
> with the radius of the earth (~6,400 km), any plane flight of a 
> considerable distance will be curved in the Euclidean sense, no matter 
> how they changed their altitude inbetween.

OK, now *I* get the joke too ;)  Sorry for being obtuse ...

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Tim Daneliuk     tundra at tundraware.com
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