Inkscape slightly moving objects between saves, how can I stop it?

[Marmotta]

I'm designing something using Inkscape that I want to send off to be cut from acrylic and I need the dimensions to be extremely accurate, however I keep finding that some objects keep being moved slightly by Inkscape when I save and reopen them. It's very obvious e.g. right now I have a rectangle placed at X 0 and Y 0 (mm) that once opened again shows as being at X -0.105 and Y -0.105. This happens all the time and is becoming incredibly annoying. Does anyone know the underlying reason for this and how I can stop it?

[brynn]

Welcome to the forum!

It's hard to say for sure.  It might be related to the type of bounding box.  The default bounding box is called Visual, and it includes the width of the stroke.  It also makes Inkscape include the width of the stroke in object dimensions.  Most people who use Inkscape for cutting, like you, switch to using the Geometric bounding box.  With that, the stroke is irrelevant to the dimension.

I suspect that Inkscape is not moving the objects, but instead is compensating for the stroke, or maybe changes of the stroke width.  Try switching to the geometric bounding box, and see if that fixes the problem.

Edit menu > Preferences > Tools > Geometric bounding box

If that doesn't fix the problem, we will investigate further.

[Lazur]

Hi.

I suspect you lowered the numeric precision in the preferences.
The more digits you set to be used the less error-prone your file savings will be.*
Although extreme transformations and/or extreme coordinates could theoretically cause problems, it's unlikely in your case.


*-Keep in mind inkscape is not a CAD software and is using cubic Béziers to represent mostly everything. There is an unavoidable rounding error that will always be present in the codes, like 0,000385 px etc.

[flamingolady]

I was going to say the same as Brynn, I believe it compensates for the stroke - deleting the stroke ought to help, but I'm not sure it will ever be perfect.  I wish we could 'lock' nodes or objects positions.