The aspect ratio for a quadrilateral is computed by the following steps, using only the corner nodes of the element (Figure 38: Quadrilateral Aspect Ratio Calculation):
If the element is not flat, the nodes are projected onto a plane passing through the average of the corner locations and perpendicular to the average of the corner normals. The remaining steps are performed on these projected locations.
Two lines are constructed that bisect the opposing pairs of element edges and which meet at the element center. In general, these lines are not perpendicular to each other or to any of the element edges.
Rectangles are constructed centered about each of the 2 lines, with edges passing through the element edge midpoints. The aspect ratio of the quadrilateral is the ratio of a longer side to a shorter side of whichever rectangle is most stretched.
The best possible quadrilateral aspect ratio, for a square, is one. A quadrilateral having an aspect ratio of 20 is shown in Figure 39: Aspect Ratios for Quadrilaterals.
For Explicit Physics Preference, Aspect Ratio (Explicit) is calculated as:
