Fusion360 Sketches - Centre Rectangles, centre shifts when updating dimensions

[digidarkroom]

Just curious why the centre of a rectangle moves when updating the dimensions of the rectangle, even though the rectangle was created from the centre outwards, it always scales towards the bottom left corner. Im guessing this is because once created the software sees a rectangle as a rectangle and doesn't take into consideration where its origin is. It can make the timeline get a bit crazy sometimes, just something Ive noticed.

[davebYYPCU]

Would be strange if that did not happen.  Change the dimension and the centre adjusts accordingly.

Might help....

[digidarkroom]

well yes I know that. my question was. why when drawing a centre rectangle (starting from the centre) and then updating dimensions why then does the rectangle scale off the bottom left corner and not scale from the centre origin? keeping the centre of the rectangle in its specified location, scaling from that point.

[TheCADWhisperer]

Define location of center point and it can’t do anything unpredictable. 
@digidarkroom 

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[davebYYPCU]

Because you obviously have allowed the centre point to be movable.

Might help....

[jeff_strater · Accepted solution]

I can shed a bit of light on this.  The constraint solver in any CAD system works pretty much the same.  It just collects a set of geometries, constraints, and dimensions, and tries to solve them.  It does not 'know' that this is a center-point rectangle.  What it sees for this is:

• 6 lines
• 5 points
• 2 dimensions
• 6 geometric constraints (parallel, perpendicular, horizontal)
• 10 coincident constraints (which bind the points to the lines)

and, the solver just tries to solve all of that geometry and constraints.  There is no such thing as a "center point rectangle" to the solver.  You can create the exact same system using the line command and the constraint/dimension commands.  If you adjust one of the dimensions, there are many solutions of this under-specified set of geometries and constraints, all of which are valid.  Technically, there are an infinite set of solutions, but, practically, that is not really the case.  The point that everyone here is making is:  Unless you give the solver a bit more of a hint about how you would like this system to react, it can choose which ever solution it "wants".  Most likely, it will choose the solution that converges the fastest.  I guess that means moving one of the points in the rectangle is the default solution.

[digidarkroom]

Thanks for that, I was wondering if the software saw and recognised an origin for things like this or if the selected starting point was just for the user’s reference, it makes sense that once created a shape would be seen as shape and not keep track of origin.

would be nice tho 🙂

[g-andresen]

Hi,

Also for a rectangle with a center point, you can specify whether the resizing should be center oriented or on a vertex.

günther