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Topic: Calculating the area of a closed 3-D path or ring
Replies: 23   Last Post: Mar 25, 2013 4:54 PM

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 Ray Koopman Posts: 3,383 Registered: 12/7/04
Re: Calculating the area of a closed 3-D path or ring
Posted: Mar 16, 2013 3:27 AM

On Mar 14, 9:36 pm, Math Guy <M...@Guy.com> wrote:
> Ray Koopman wrote:
>>
>> You haven't said whether the ordering of the points around the
>> loop is given or not.

>
> The user will specify the markers to be used (there are other markers
> on the heart which will not be involved in this ring). A routine will
> identify the order by picking one point and then determine which of
> the remaining points is closest, and will piece-wise work it's way
> around the ring. This should avoid any errors if the user gives the
> order incorrectly.
>

>> Also, what do you want to do if the loop is not convex?
>
> Do you mean what if the loop looks like a potato chip with a bite taken
> out of it?
>
> I don't see how that would affect the proposed area calculation method.

It won't affect the plane of best fit, but it may make it harder to
identify the loop. I would give the 2D coordinates to a convex hull
routine. If the hull uses all the points then it's your loop. But
if some points are inside the hull then a simple nearest-neighbor
approach can sometimes connect the points in the wrong order.

Date Subject Author
3/12/13 Math Guy
3/13/13 Ray Koopman
3/13/13 Narasimham
3/14/13 Narasimham
3/13/13 Shmuel (Seymour J.) Metz
3/13/13 Frederick Williams
3/13/13 Brian Q. Hutchings
3/14/13 fom
3/14/13 fom
3/14/13 Math Guy
3/15/13 Ray Koopman
3/15/13 Math Guy
3/15/13 fom
3/16/13 Ray Koopman
3/16/13 fom
3/16/13 Math Guy
3/16/13 fom
3/16/13 Ray Koopman
3/15/13 Peter Spellucci
3/16/13 Math Guy
3/17/13 Ray Koopman
3/17/13 Math Guy
3/18/13 Ray Koopman
3/25/13 Gib Bogle