What Datum Lines Does PrusaSlicer Use to Generate Layers?
When PrusaSlicer generates layers, does it slice the model through middle, top, or bottom of the layer height?
Say for instance I have a part that is 10mm tall with 0.2mm layer height. Will PrusaSlicer slice the model exactly through the 10mm height, 9.8mm, or through 9.9mm to generate that last layer? If the object were modeled at 9.9mm tall, would it consistently know whether or not to give it an extra layer? In other words, if it is through the middle, and the object ends in the middle of the layer midline, will PrusaSlicer have trouble discerning whether or not to round up or down?
I ask because I ran into an issue earlier where this might be important to know. I was printing two objects at 0.2mm layer height. At 8.5mm, both have a flat top surface, thus they should have top layers at the same height. However, the top layer on one turned out to be 8.4mm and the other turned out 8.6mm. As it turns out, I looked at the file in Slicer, and one object had an extra layer while the other didn't. That said, this issue does not concern the accuracy of my printer. Also, I double checked the height of both models and both are exactly 8.5mm in that area. Plus, the model does not have any open edges, so I believe this doesn't concern the accuracy of the model either.
If PrusaSlicer generates layers through the midpoint of the layer, perhaps this issue means the program has issues with slicing directly through edges? I know that sometimes when I create contours in my my 3D modeling program (Rhino 3D) that if it cuts exactly along the edge of an object, it has trouble calculating it, so sometimes it works and other times it doesn't. Perhaps that is the issue here?
Anyway, thank you so much in advance for all of your help! I'm just wondering how I should model my parts to make my results most predictable, and hopefully this will help everyone else too. (:
RE:
Update: It appears that the Slicer generates contours by slicing through the midpoint of the layer. In a test run, I sliced objects that were 10.05mm, 10.1mm, and 10.15mm in height. The object that was below the midpoint at 10.05mm remained at 10mm while the others increased to 10.2mm. That said, given my earlier example in this post, it appears that PrusaSlicer is inconsistent with detecting an exact intersection with objects that end right at that midline. So I suppose if layer count is super important for you, make sure to model exactly what height you want down to the layer height resolution you need (: