[Gmsh] How are the display points of volumes calculated?

[Christophe Geuzaine]

Neilen Marais wrote:
> Hi,
> 
> I'm a bit confused about how gmsh is displaying volumes (i.e. the yellow 
> ball that represents a volume). I always assumed it was put at the 
> centroid of the object, but this doesn't seem to be the case (unless my 
> math is all wrong).

the point is put at the center of the bounding box of the volume



> 
> An example:
> 
> Point(1) = {14.5,11.5,9.5,1000000};
> Point(2) = {14.5,11.5,19,1000000};
> Point(3) = {14.5,23,9.5,1000000};
> Point(4) = {14.5,23,19,1000000};
> Point(5) = {21.750725,17.25,14.25,1000000};Line(1) = {1,2};
> Line(2) = {2,4};
> Line(3) = {4,3};
> Line(4) = {3,1};
> Line(5) = {1,5};
> Line(6) = {2,5};
> Line(7) = {4,5};
> Line(8) = {3,5};
> Line(9) = {2,3};
> Line Loop(10) = {3,8,-7};
> Plane Surface(11) = {10};
> Line Loop(12) = {2,7,-6};
> Plane Surface(13) = {12};
> Line Loop(14) = {6,-8,-9};
> Plane Surface(15) = {14};
> Line Loop(16) = {5,-8,4};
> Plane Surface(17) = {16};
> Line Loop(18) = {6,-5,1};
> Plane Surface(19) = {18};
> Line Loop(20) = {2,3,-9};
> Plane Surface(21) = {20};
> Line Loop(22) = {1,9,4};
> Plane Surface(23) = {22};
> Surface Loop(24) = {19,17,23,15};
> Volume(25) = {24};
> Surface Loop(26) = {15,13,21,11};
> Volume(27) = {26};
> 
> In this case the two volume points are drawn on top of each other, 
> wherease the respective centroids (which for a tets are the average of 
> the for vertices) should be [16.31268125,  15.8125    ,  13.0625] and 
> [16.31268125,  18.6875    ,  15.4375]
> 
> So then, my question is: How is that display point calculated (assuming 
> my math is good :)
> 
> Thanks
> Neilen
> 
> 
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> 
> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine