why is this important ? If a user is concerned about mathematical purity he should use Mathematica and not FreeCAD.
why does it need to ? What happens if it doesn't ? What problem are you trying to solve ? A center and coordinate system are provided by default, out of convenience (inheritence), if a user doesn't need/want them he can silently ignore them.3. The implementation of a plane creation tool in freecad which needs to reconcile both concepts 1. and 2.
Cheers,DeepSOIC wrote: ↑Fri Aug 30, 2019 4:52 pmSo, for a potential developer (me, possibly), here's a list of things to do.
* add CS marker to datum planes, at least for the time it is being attached.
(that way, it will be easier to understand what roll,pitch and yaw do)
* (if possible) make datum plane's top and bottom look different.
* new attachment mode for sketches, to treat a plane as a plane.
* make the new attachment mode default for sketches made on datum planes.
* an option in preferences to change it back, for those who can't adapt to use LCS instead of a datum plane.
* make it easy to attach sketches to LCS object in PartDesign.
Does that sound good?
1) that's the situation today (yes, a Datum Point in FreeCAD is also an LCS internally).saso wrote: ↑Sun Sep 01, 2019 10:11 amit makes no sense for a plane to have an origin (center) by itself. following the logic that it could be added because of convenience or because it is constructed (in some cases) like that, would mean that for the same reasons we can also add this to the datum point and line, result would be that we would have 4 datum elements that are basically all the same, an LCS.
This exactly what I wanted to say! Also, what is the problem with displaying the underlying LCS during creation? It does not change functionality, the plane is the same as before and will be displayed the same as before after creation, it only makes it easier to understand the controls. I don't see the benefit in removing the LCS either, the plane works just the same.Zolko wrote: ↑Sun Sep 01, 2019 3:01 pm1) that's the situation today (yes, a Datum Point in FreeCAD is also an LCS internally).saso wrote: ↑Sun Sep 01, 2019 10:11 amit makes no sense for a plane to have an origin (center) by itself. following the logic that it could be added because of convenience or because it is constructed (in some cases) like that, would mean that for the same reasons we can also add this to the datum point and line, result would be that we would have 4 datum elements that are basically all the same, an LCS.
2) yes, it makes sense from a software point of view: all FreeCAD objects have a Placement (even a chamfer: how ridiculous is that ? It has no use-case, but it's there because it's inherited), and a Placement is a bijective transformation in space, i.e. an local coordinate system.
3) it is not "added" but "built-in" : if you don't want it, it must be actively removed.
4) just out of curiosity : if you place 3 sketches on the same datum plane in your favorite CAD system, will these 3 sketches have their respective origins placed randomly all over the plane, or will they be all in the same place ? If it's the latter, how do you explain it apart that the datum plane itself has an origin, and all sketches are placed on that origin by default ?
5) you still didn't explain: what is the problem you try to solve ? Why can't you simply ignore a datum plane's origin ?
I don't understand what is the conflict with this and the request to display LCS during creation? You can have both, putting sketches on the plane's LCS is just the default.
this already exists and works: select the sketch (in th tree), select MapMode, then select the vertex (point) on the plane where you want the origin to be, as second reference select the datum plane as in "Tangent to Surface", and your sketch is on the plane but its origin is not the origin of the plane. It's probably possible to also orient the sketch's axis, I let you discover that.