Talk:Centroid

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[edit] Centroid = center of mass?

From WordNet (r) 2.0 (August 2003) [wn]:
  centroid
      n : the center of mass of an object of uniform density

WordNet says, the center of mass is called centroid when the object has uniform density distribution. Is it ture?

Not exactly. When the object has an uniform density distribution, the centre of mass coincides with the object's geometric centre. Yet, the names of the concepts remain the same, which means that a centroid is still a centroid and a centre of mass is still a centre of mass --Maciel 11:35, 25 Sep 2004 (UTC)
I agree with both of you. On a very slightly different note I've never seen a text that equates the physical center of mass with its "centroid", unlike the current version of the introduction: "In physics, the words centroid and barycenter may mean either the center of mass or the center of gravity of an object, depending on context." Weisstein's physicsworld page partially supports this usage, but he cites no sources, and I'm more inclined to think he's just wrong. I'll change the intro to be more conservative. Melchoir 04:06, 19 April 2006 (UTC)

[edit] Centroid = intersection of bisecting planes (NOT)

In geometry, the centroid or barycenter of an object X in n-dimensional space is the intersection of all hyperplanes that divide X into two halves of equal measure.

This is wrong. The line parallel to one side of a triangle that divides it in half is sqrt(1/2) from the opposite corner, not 2/3, which is where the centroid is. -phma 21:06, 26 Jul 2004 (UTC)

Oops! Thanks... Jorge Stolfi 23:26, 15 Sep 2004 (UTC)

[edit] Centroid of a circle

Does anyone know what the formula for the centroid of a circle is? I tried to derive it, but it didn't work. I can't find it online, either. Can anyone tell me what it is?

--Gscshoyru 17:42, 17 September 2005 (UTC)

Isn't it just the center?.... and if it isn't just use the formula in the article, with the circle centered at the origin. the y value is given by int(1/2*f(x)^2 from a to b) divided by the area. Xunflash 04:28, 30 October 2005 (UTC)

Yes, at the center, compare Point_groups_in_three_dimensions#Center_of_symmetry.--Patrick 11:07, 30 October 2005 (UTC)

[edit] Programming the centroid computation

Just a minor edit how to calculate centroid of a triangle using programming. I am sure someone will find it useful. SnegoviK 12:22, 24 February 2006 (UTC)

Good try, but unfortunately that whole section seems quite pointless. The previous section already says that the centroid of a triangle is obtained by averaging the coordinates of the corners; that is all one needs to know in order to solve your programming exercise. Why would the reader want to know other (incorrect!) ways of doing it? Besides, this is a geometry article; computer language details do not belong here.
But please do not get discouraged, surely you will find many other ways to help Wikipedia.
All the best, Jorge Stolfi 17:06, 24 February 2006 (UTC)
I just realised that you are absolutely right! I am sorry I didn't manage to come with a resourceful article, I will try harder next time. Your comment is very helpful to me, thanks. ;) SnegoviK 19:33, 24 February 2006 (UTC)

Revision as of 21:29, 15 August 2006 (edit) 129.110.8.39 (Talk)

[edit] Vanity Ref?

An anon at 129.110.8.39 (pc0839.utdallas.edu) added the reference:

+  ==References==
+       *\{\{cite paper | author=Abdi, H | title = [1] ((2007). Centroid, center of gravity, center of mass, barycenter. In N.J. Salkind (Ed.): Encyclopedia of Measurement and Statistics. Thousand Oaks (CA): Sage.| year = 2007 |\}\}

Someone might want to check whether this is a worthwhile addition. Lunch 22:32, 1 September 2006 (UTC)

[edit] Centroids in GIS systems

In Geographic information systems, the term centroid may refer to other points than the geometric centre, primarily because of the desire that the centroid is inside the object. See for example [2]. Apus 08:24, 11 October 2006 (UTC)

[edit] Suspected Excessive Promotion of Herve Abdi

Another reference to Herve Abdi! Inserted by an anonymous user with ip address 129.110.8.39 which seems to belong to the University of Texas at Dallas. Apparently the only editing activity so far has been to insert excessive references to publications by Herve Abdi (of the University of Texas at Dallas). The effect is that many Wikipedia articles on serious scientific topics currently are citing numerous rather obscure publications by Abdi et al, while ignoring much more influential original publications by others. I think this constitutes an abuse of Wikipedia. As a matter of decency, I suggest to 129.110.8.39 to remove all the inappropriate references in the numerous articles edited by 129.110.8.39 , before others do it. Truecobb 20:20, 14 April 2007 (UTC)

I have waited for several months; now I'll delete the obscure reference. Truecobb 21:23, 15 July 2007 (UTC)

[edit] missing pic

I didn't feel comfortable editing this page but felt I should point out that one image on this page does not appear for me.

The image Triangle_centroid_1.svg is on the page but appears not to contain anything. Clicking on the image yields http://en.wikipedia.org/wiki/Image:Triangle_centroid_1.svg which also appears not to contain anything. However, clicking on the image on that page yields a URL which does have a non-empty image http://upload.wikimedia.org/wikipedia/commons/8/85/Triangle_centroid_1.svg

--128.89.80.117 20:00, 29 October 2007 (UTC) Dan B.

I modified the svg file on commons to work better, I hope. It may take a while for the modified image to propagate back here through the various levels of caching we have. —David Eppstein 20:29, 29 October 2007 (UTC)

[edit] Proof that the centroid of a triangle divides each median in the ratio 2:1

This proof is not a proof. It is based on the statement that GBOC is a parallelogram, which is not proved.

Paolo.dL (talk) 09:38, 19 February 2008 (UTC)

I've fixed the hole in the proof. Occultations (talk) 02:57, 20 February 2008 (UTC)