# 1.11.3 Three-Dimensional Optimized Rectangles

Instead of specifying all the vertices for a three-dimensional rectangle (a polygon in the shape of rectangle in three-dimensional space), you can represent the rectangle by specifying just the two corners corresponding to the minimum ordinate values (min-corner) and the maximum ordinate values (max-corner) for the X, Y, and Z dimensions.

The orientation of a three-dimensional rectangle defined in this way is as follows:

• If the rectangle is specified as <min-corner, max-corner>, the normal points in the positive direction of the perpendicular third dimension.

• If the rectangle is specified as <max-corner, min-corner>, the normal points in the negative direction of the perpendicular third dimension.

For example, if the rectangle is in the XY plane and the order of the vertices is <min-corner, max-corner>, the normal is along the positive Z-axis; but if the order is <max-corner, min-corner>, the normal is along the negative Z-axis.

Using these orientation rules for rectangles, you can specify the order of the min-corner and max-corner vertices for a rectangle appropriately so that the following requirements are met:

• The normal for each polygon in a solid always points outward from the solid when the rectangle is part of the solid.

• An inner rectangle polygon is oriented in the reverse direction as its outer when the rectangle is part of a surface.