Official Zentangle® Pattern - Impossible Fragment & Reticula

Rick Roberts demonstrates how to draw this pattern called "Impossible" in a Kitchen Table Tangles video that you can watch if you have the Zentangle Mosaic app. First he draws a triangle grid then he fills each triangle with this fragment:

Every other fragment is reversed to create the illusion of three dimensions. The shading helps to enhance the illusion even more. All of the fragments that point to the right are drawn one way and all of the left-pointing fragments are drawn as mirror images of the right-pointing triangles. If you can remember that, this is not too difficult to draw.

Rick is pretty vague on how to draw the triangle grid (reticula) so I came up with my own method where I start with a box grid drawn in pencil. Once I have my grid, I divide the squares into triangles like this:

I make little marks with my pencil at the center points of the squares. I drew two example triangles so that you can see how I connect the lines.

Above you can see that I have filled the grid with triangles. I have indicated with red dots where those pencil marks were. After I have drawn the triangles, I erase the pencil lines and turn my tile sideways which is the proper orientation for drawing "Impossible". I find it easier to draw the triangles with the tile turned the other way and then rotate it later. Here is a small sample where I have outlined with a bold black pen the six fragments that make up this drawing so that you can see them better.

The tile below shows my first attempt to draw this after watching the video:

Once I understood the concept, I drew this tile:

The tile at the top of this post was my third "Impossible" drawing.