Illustrator: problem with the 3D effect - Extrude and bevel, Isometric lines aren't straight

Question

I've this problem with the 3D effect: the vertical lines projected by the effect aren't vertical.

I start with a plane shape like a rectangle and I select the isometric top preset in the effect and this is what it happens.

In the isometric view the vertical lines are supposed to be perpendicular to the ground, right? I mean, if I draw the same shape in the isometric grid the vertical lines are really vertical. I miss something.

The object in the image is the same but reflected for a view of the problem.

Thanks for the attention.

Answer 1

Illustrator's 3D effect is local, meaning relative to the object. It is never relative to the document or anything else. You can't create a 3D "scene" in Illustrator using the effect without a great deal of irrational alterations to each and every object.

It is merely a lesson in frustration if you wish to have multiple objects using the 3D effect align as if they were a "scene". There's no such thing as a "scene" in Illustrator.

Isometrics in Illustrator are most commonly created via a grid and manually drawing extrusions, the 3D effect is not generally a viable alternative to this.

Answer 2

I believe the view angles - especially the one about 35 degrees - are not exact in 3D Extrude&Bevel effect. I guess 35 degrees is the used value, but in geometry its should be arctan(1/sqrt(2)) which is with 4 decimals about 35.2644 degrees.

I cannot prove the error is this, because a preset could in theory have internally more accurate numbers, no matter the user interface doesn't allow to type nor show them.

BUT: all vertical lines should be tilted to the same direction. The edges should still fit if you do not flip nor rotate any of the items after extruding.

You can test it by applying Object > Expand Appearance to 2 extruded objects which both have the same isometric view setting and zero perspective. In my tests vertical edges snap perfectly. Of course that proves nothing of rendering in another system which has different graphics card (+its software) and maybe different Illustrator version, too.