Hi,

When specifying relations in 3D sketch, there are two relations called "ParallelYZ" "ParallelZX" which I found difficult to understand. Its help at http://help.solidworks.com/2011/English/SolidWorks/sldworks/LegacyHelp/Sldworks/SW_Sketch/Sketch_Relations.htm describes very much unclearly as:

Relation | Entities to select | Resulting relations |

Horizontal or Vertical | One or more lines or two or more points. | The lines become horizontal or vertical (as defined by the current sketch space). Points are aligned horizontally or vertically. |

Collinear | Two or more lines. | The items lie on the same infinite line. |

Coradial | Two or more arcs. | The items share the same centerpoint and radius. |

Perpendicular | Two lines. | The two items are perpendicular to each other. |

Parallel | Two or more lines. A line and a plane (or a planar face) in a 3D sketch. | The items are parallel to each other. The line is parallel to the selected plane. |

ParallelYZ | A line and a plane (or a planar face) in a 3D sketch. | The line is parallel to the YZ plane with respect to the selected plane. |

ParallelZX | A line and a plane (or a planar face) in a 3D sketch. | The line is parallel to the ZX plane with respect to the selected plane. |

I cannot figure out what exactly "with respect to the selected plane" means. Does it mean the line's projection onto the selected plane?

On the other hand, when intially the either "ParallelYZ" or "ParallelZX" is not satisfied, does SW rotate/change the line or the plane? If the line is fixed (both ends), what will happen? If the line is not fixed, what else would happen?

And is this a commonly used relation? Matt Lombard's SolidWorks 2011 Parts Bible doesn't have a single line about it; there is also virtually no Google search (including Youtube video) about it. I guess it is among one of the rarely used features?

Qi

Nice find Qi. These relation are just updating the local coordinate system for the XYZ directions based on the selected plane. It is quite similar to CTRL-preselecting the plane and drawing the line after that, as I told you in your other thread.

Take a look at the attached file.