# Re: determine the area on slice

From: Wanchai Rattanawong (wratta@swin.edu.au)
Date: Sat Mar 04 2000 - 01:22:43 EET

Dear Irene Quinlan

Thank you very much for your suggestion. Your way is the same as my way.
My problem is if I have a hole, this formulas can't do it. What do you mean,
subtract the area of the holes from the outer areas.? On the STL file,
sometimes the points are not the order and how the program know that this is
the hole. Could you recommend for me please? I am so appreciate.

> Wanchai -
>
> The area of a 2D polygon can be calculated by
> polygon = set of points {P1, ... PN}
> area = (P1 X P2 + P2 X P3 + ... PN-1 X PN + PN X P1) / 2
> where X is a vector cross product, and
> P1 X P2 = (P1.x * P2.y) - (P1.y * P2.x)
>
> Don't forget to subtract the area of the holes from the outer areas.
>
>
> Sanders Prototype, Inc.
>
>
> Wanchai Rattanawong wrote:
> >
> > Dear everyone
> >
> > Can anyone suggest me how to determine the area on each layer? Assume
> > that we have many points on one slice.
> >
> > Best regards,
> > Wanchai Rattanawong
> > Industrial Research Institute Swinburne (IRIS)
> > P.O. BOX 218, Hawthorn
> > Victoria 3122, Australia
> > Tel:(613)9214 5654 Fax:(613) 9214 5050
> > Email: wratta@swin.edu.au
> >
> > For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
>