Jee-Bee wrote: ↑Tue May 08, 2018 5:24 am
In some branches it is common to have a common place of that product as the reference point. That point is the reference point for all geometry.
For my feeling all objects should have a reference to an point otherwise the objects are floating around. A lot of CAD packages are able to place the first part on origin for that reason.
I think when Freecad can use of skelton parts that it make it easy to work even on lower levels with global coordinates.
Yes, that's it. In the CAD packages I've worked with, assemblies and parts have an origin point, 3 axes, and 3 planes that define a fixed (absolute and unchanging) frame of reference, so that no matter what changes are made during the modelling, there is always a "home" location and orientation to refer to.
When starting a new assembly, the first thing I do is place the first part and orient it with respect to the coordinate system of the assembly. Usually that part will contact the origin point somewhere logical. The planes have meaning to me as well: XZ is a horizontal plane, parallel with the "ground", XY is the vertical front/back plane, and XZ is the vertical side-to-side plane.
Once positioned and oriented with respect to the assembly coordinate system, that first part is locked in place and remains completely immovable. The next part placed will be placed with some relation to the first part- maybe fixed or maybe with freedom with some relative movement. But there is always at least one part that stays where it is, and always a coordinate system to define where "where" is.