!! New version penrose5.stl with a couple of wayward vertices fixed !!This is a 3D-printable version of the Penrose Triangle illusion, based solely on the 1934 design painted by Swedish artist Oscar Reutersvärd. The design also appeared on Swedish postage stamps in the early 1980s.I created this 3D design entirely from scratch using the process outlined in the "Instructions" section below. This work is based solely on Oscar Reutersvärd's design, although some elements are inspired by the Hollow-Face illusion discovered many decades (if not centuries) ago.This model contains a number of notable improvements over previous 3D representations:1) It is parallax-corrected for a viewing distance of 40cm, i.e. it will look exactly like Oscar Reutersvärd's design, with cubes lining up on all 3 sides simultaneously. This is a great visual improvement over previous versions, which only lined up on 2 sides simultaneously.2) It has been resized (to 99.43 x 99.65mm) to make maximum use of the Makerbot build envelope.3) The top edges are now tapered so as to make the most of your printer's capabilities. The better your printer, the sharper the edges will be.4) I own the copyright to this 3D design, and hereby distribute it under the "Attribution/Non-Commercial/Share-Alike" licence for all non-profit parties to print, improve and share.Simply print! No support required.NB: I have uploaded a new penrose4.stl file, which has better poly orientation to ensure that the walls build up gradually.There is also now a new penrose4_braced.stl file which includes bracing to help keep the blocks in the right position during the first half of the print!You can create your own Penrose Triangle illusion very easily by following these steps in your favourite 3D software. A photo has been attached for each step.1) Create an image plane containing the image you are trying to portray. Then create a camera at a suitable viewing distance from the image plane (e.g. 40cm) 2) Create a cube, rotate it so it matches a cube in the image, delete the top 3 faces and then duplicate it 8 times. Lay them out roughly. 3) Viewing from the camera created in step 1, pull the vertices in X and Y until they line up with the image. This corrects for parallax error since we are working from the intended viewpoint perspective, and not an orthographic view. 4) Cut out the bits you don't want, referring back to the image if you need to. Once done, stitch everything together into one surface. 5) Extrude the stitched surface up or down and then widen the bases of each cube if you want. Done!Making your own 3D Penrose Triangle model clearly isn't rocket science. In fact, it would make a very good practice exercise for first-year 3D art/design students!