Creating 3D, Solid, and Watertight Geometry
These are all great questions! A key distinction in SketchUp is the difference between 3D (three-dimensional) and Solid or Watertight Geometry. We can explain the differences by answering the previous questions.
Q: What makes a SketchUp model 3D?
A: All SketchUp models exist in the 3D Drawing Area. Also, all Geometry has X, Y, and Z coordinates. So, all Geometry exists in 3D space. But we would not call an Edge or single Face 3D Geometry—it is the collection of many Edges and Faces that sit on the Red, Green, and Blue Axes that create true 3D Geometry.
Q: Are 2D Shapes 3D, Solid, or Watertight Geometry?
A: 2D Shapes are technically in the 3D Drawing Area in SketchUp. And, even if the Z (Blue Axis) value is 0, it is still counted! But 2D Geometry cannot be Solid or Watertight—because it is flat! Solid and Watertight Geometry requires that there is space inside the object—space that could be completely filled...