MassProperties.Centroid is Incorrect

[junoj]

I have tried just about everything and the mass properties center point of gravity is coming out incorrect. Any advice would be much appreciated.

I have created a box 300x300x300 with the center of the box at 0,0,0 (for testing the cg) . The result I get is not 0,0,0  one of the values always comes out to be not zero, depending on the orientation of the box. Is this a bug?

Dim cg As Point3d = T.MassProperties.Centroid
MsgBox(cg.X & vbCr & cg.Y & vbCr & cg.Z)

 Thank you,

-Jay

[Hallex]

Have you tried:

MsgBox(string.Format("{0:f6};{1:f6}[2:f6}",cg.X, cg.Y, cg.Z))

~'J'~

[junoj]

Hi and thank you Hallex,

The problem is not in the msgbox. The problem is that the MassProperties-Centroid is not giving the centroid.

For instance if I create a box 300,300,300 and place the center of the box at 0,0,0 when I run my code I get:

X = 0

Y = -1.07610739413994E-14

Z = 0

The X,Y,Z should be all equal to zero, but that's not the case.

[_gile]

Hi,

X = 0

Y = -1.07610739413994E-14

Z = 0

means:

X = 0

Y = -0.00000000000000107610739413994

Z = 0

Which is quite close to: 0, 0, 0

This is not inherent to the API nor to autoCAD, this little lack of accuracy is due to the double-precision floating-point format used to encode real numbers.

See here:

http://en.wikipedia.org/wiki/Double-precision_floating-point_format

Note:

Point3d pt = new Point3d(0.0, -1.07610739413994E-14, 0.0);
pt.IsEqualTo(Point3d.Origin);

 returns true (IsEqualTo() uses the 'global tolerance')

[junoj]

Very interesting. I have a very large file with thousands of solid pieces, is there a way to obtain the CG of all pieces or will I have to run each piece and add up all the CGs. I would like to run a quick test on a large file to see if the output is the same as the Mass Prop output

Thank you everyone for helping me.

-j