Sketch plane mapping is lost when going back in history

[vasilis]

I was trying to learn FreeCAD (Version 18.4) by following the tutorial on the page
https://wiki.freecadweb.org/Basic_Part_ ... torial_017
when I arrived to the end I've tried to "re-edit" the previous pads to add the "refine" property to true
and by doing so the sketch003 that was mapped on the titled surface it changed mapping and moved in the middle of the free space.
Then trying to re-edit all previous steps several things are happening like the body disappears, the sketch is moving etc.

[TheMarkster]

Probably this is the topological naming issue. The problem is likely due to the use of links to external geometry. When refining the object some of the edges and faces get removed causing the remaining faces and edges to get renamed, for example what was Face7 might now be Face5 or what was Edge12 now is Edge7. When this type of thing happens and you had links to external geometry to one of those subobjects that have now been renamed this can cause problems with the model. It is generally more robust to create links to external geometry to the sketches that the solid is based upon rather than upon the solid edge, face, or vertex. Even better would be the use of expressions, for example named constraints or cells from a spreadsheet as references. The topological naming issue is one that is very well known and has plagued FreeCAD for some time. The good news is there is a fix in the works, likely (hopefully) to make it into the 0.20 development cycle.

[vasilis]

Many thanks for your reply.

It makes sense what you say.
How can I remap a sketch after refining? I've tried the "Map a sketch to a face" with no success.

Would it be useful that each sketch keeps cached the coordinates of the sketch plane,
so if for some reason the ref is lost, to use the cached information. Right now what happens
the sketch is shown as being in mid-air

[vasilis]

I found another way
Then find the name of the new face by clicking on it (seeing the name on the statusbar)
Select the "Sketch" -> "Data" -> "Map Mode" click on the "..."
Click on the "Plane" and select the face or edit by hand

Not very intuitive but works