Re: how to compute the surface defined by a given contour?

[Ben Abbott]

On Dec 11, 2010, at 4:18 AM, Christophe Trophime wrote:

> 
> On Dec 11, 2010, at 2:17 AM, Ben Abbott wrote:
> 
>> On Dec 10, 2010, at 9:29 AM, trophime wrote:
>> 
>>> Hi,
>>> I am a newbie to octave.
>>> I have X Y Z data. I have manage to plot contour of Z as a function of
>>> X,Y using something like :
>>> 
>>> x = linspace(0, 0.1197, 101);
>>> y = linspace(0.113258, 0.377527, 101);
>>> Z = load("data");
>>> 
>>> [X,Y] = meshgrid(x, y);
>>> surf(X,Y,Z)
>>> contour (X, Y, Z)
>>> 
>>> Then I have selected a given contour :
>>> 
>>> VN = [0.5, 0.5];
>>> contour (Z, VN);
>>> [C, LEV] = contourc (X, Y, Z, VN);
>>> 
>>> Now I would like to get the surface (in the (X,Y) plane) defined by this
>>> contour?
>>> Is it possible to compute the gravity point of the contour?
>>> 
>>> Thanks for your helps
>> 
>> If I understand what you'd like to do, an approximation to the center of 
>> gravity can be calculated as ...
>> 
>>      center = sum (((X+1i*Y).*Z)(:)) / sum (Z(:))
>>      x_center = real (center)
>>      y_center = imag (center)
> 
> Yes but I want the center of gravity of the surface defined by a given 
> contour?
> I other words I want to extract X and Y from C provided by "contourc" for a 
> given value to define a surface,
> compute its area and its center of gravity.
> 
> Thanks
> C.

You'd like to treat the distributed mass as proportional to the surface's area?

Do I understand correctly? 

Ben