# Miscalibration, circles turn into ellipses

Maxim,

Extend all backers warranty to another 3 months .

I’m very reasonable.

Maxim,

I was thinking that Formlab already had this re-calibration/ fine tune feature built in at early design stage.

Should extend warranty to another few months after Formlab found good solution to it.

Wonder if is it possible to apply “calibration function” to a STL model in some CAD. This function shall be inverse to Y=kX+b calculated from measurements. Is there such functionality in Solidworks, AutoCAD? This way it could be possible to distort model in opposite way the printer distorts it so result should be zero distortion.
Googled this question for some time. Key word is ‘transformation matrix’. Here one may find general approach to 3D transformation in AutoCAD http://through-the-interface.typepad.com/through_the_interface/2010/12/a-simple-command-to-perform-a-matrix-transformation-on-an-autocad-entity-using-net.html
For SolidWorks as well - http://help.solidworks.com/2013/English/api/sldworksapi/SolidWorks.Interop.sldworks~SolidWorks.Interop.sldworks.IMathUtility~CreateTransform.html
I don’t have deep understanding of any current CAD system - so your advice and opinion is very much appreciated.

Good day Andrey,

(just copying, my answer in from my blog)
You are thinking the right way for the calibration, this is how Preform already works. They compute a laser path then apply some deformation to compute the final galvanometers angles signal.
So, to correct scaling mismatch, you ‘just’ have to multiply any points by a ‘scaleFactor’ (in your Xnew = scaleFactor * Xorg + OffsetCst). But the constant will only add an offset to the position of the object.
In my article, I’ve shown that there is also laser diameter mismatch that will be more complex to compensate.  In this case each point of the mesh will need to be moved in/out in the surface normal direction. That transform cannot be expressed with a simple global matrix transform as the direction is local.
But that could be a fun utility to program, I’ll see if I have some time in the coming days.
Cheers