Front Face Back face?


#1

Hi,

Been using sketchup for a while now But !!
I still don’t know the significance of front face back face ? can any one enlighten me ?


#2

Face orientation tells other software which way things are facing for a number of reasons.
Many render engines ignore back faces, to help reduce the amount of work they do, so if faces are reversed it doesn’t see the materials.
3d printing needs to know what is inside and what is out, imagine a cube with the back faces all facing out, technically the print software would see that as in infinite cube with a cube shaped void at its center, which would be kinda difficult for it to print.


#3

@Box hit many of the high points. Here’s another that might not occur to a newbie.

In the real world, things are filled with solid material. That provides natural and instinctive notions of “inside” and “outside” and the boundary between them: inside is where the solid stuff is, outside is where you are. But SketchUp is a “surface modeler”. It doesn’t know about solid stuff. It uses infinitely thin planar polygons to define the boundary. Those polygons have two sides. The orientation of those two sides is how SketchUp identifies which side of the boundary is outside (front face) vs inside (back face). So, consistent orientation of front vs back is what makes your SketchUp model represent something real vs an imaginary thing with no consistent inside or outside.


#4

Thank you both.


#5

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