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ID | Project | Category | View Status | Date Submitted | Last Update | ||||||||

0031290 | Community | [OCCT] OCCT:Modeling Algorithms | public | 2020-01-01 21:43 | 2020-01-15 12:15 | ||||||||

Reporter | b_walter | ||||||||||||

Assigned To | msv | ||||||||||||

Priority | normal | Severity | minor | ||||||||||

Status | new | Resolution | open | ||||||||||

Platform | Mac | OS | OS | OS Version | X | ||||||||

Product Version | [OCCT] 7.3.0 | ||||||||||||

Target Version | Fixed in Version | ||||||||||||

Summary | 0031290: Modeling Algorithms - Center of mass of the TopoDS_Edge of an ellipse seems to be wrong | ||||||||||||

Description | I use opencascade 7.4.0_1 If I create an ellipse with the following code ``` gp_Pnt center(0., 0., 0.); gp_Dir zDir = gp::DZ(); gp_Ax2 axis(center, zDir); gp_Elips ellipse_gp(axis, 4000., 40.); TopoDS_Edge ellipse = BRepBuilderAPI_MakeEdge(ellipse_gp); ``` then calculating the center of mass by ``` GProp_GProps Properties; BRepGProp::LinearProperties(ellipse, Properties); gp_Pnt c = Properties.CentreOfMass(); ``` leads to (-81.295066, 0.000000, 0.000000) I would have expected (0, 0, 0). What happens here? | ||||||||||||

Steps To Reproduce | ellipse el 0 0 0 4000 40 mkedge e el lprops e Center of gravity : X = -81.2951 Y = 1.40172e-15 Z = 0 | ||||||||||||

Tags | No tags attached. | ||||||||||||

Test case number | |||||||||||||

Attached Files | |||||||||||||

Notes | |

(0089836) msv (developer) 2020-01-01 23:25 |
This seems to be a bug in calculation of linear properties of an ellipse. Workaround is to create a face of that ellipse and to compute surface properties of that face. The computed center of such face is (0, -3.91083e-15, 0). |

(0089837) b_walter (reporter) 2020-01-02 15:48 |
As a side note, if I approximate the ellipse with points (python code for illustration) ``` def ellipse(maj_r, min_r, alpha): return (maj_r * math.cos(alpha), min_r * math.sin(alpha)) alphas = np.linspace(0, 2*math.pi, 3601) points = [ellipse(400, 10, alpha) for alpha in alphas] ``` and build a closed wire, the center of mass is correct. So it is not a matter of the shape dimensions or the shape form, but of the ellipse itself. |

Issue History | |||

Date Modified | Username | Field | Change |

2020-01-01 21:43 | b_walter | New Issue | |

2020-01-01 21:43 | b_walter | Assigned To | => msv |

2020-01-01 23:25 | msv | Note Added: 0089836 | |

2020-01-01 23:26 | msv | Steps to Reproduce Updated | View Revisions |

2020-01-02 15:48 | b_walter | Note Added: 0089837 | |

2020-01-15 12:14 | kgv | Summary | Center of mass of the TopoDS_Edge of an ellipse seems to be wrong => Modeling Algorithms - Center of mass of the TopoDS_Edge of an ellipse seems to be wrong |

2020-01-15 12:15 | kgv | Relationship added | related to 0030449 |

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