Before we dive into this section, it is important to go over a few terms that will become important not only in this article, but most articles concerning the PAT. Differentiating these terms will give you a greater appreciation of how PAT questions are created and will therefore be advantageous when deciding on an answer choice during exam time.
Perspective Vs. Orthographic
Orthographic view is something we don’t see in the real world so let us start with this. This view is frequently used in engineering and architecture as it portrays measurements and communicated dimensions unambiguously. Every unit length on object will be appear to have the same length on all edges. This view arises when the distance of the viewer to the object is infinity because this is the point at which light rays will be completely parallel. The 3D representation and the answer choices in the aperture section can be said to be an orthographic representation of the object’s respective sides.
Perspective view is what you see the world every day. Even if the edges of an object are identical in length, the phenomenon of fore-shortening will make it appear otherwise (Edges close to the viewer will appear bigger then edges further from the viewer). Perspective view is highly dependent on the object’s distance from the viewer and angle of view itself. This view also makes it more difficult to judge dimensions of edges in relation to each other. Below is an animation showing what happens to the appearance of an object when distance and angle of view are changed.
What does this mean to you?
In addition to the above two projection styles, there are many more different ways we can use to portray 3D objects on a 2D plane and understanding the above will give you a greater appreciation of how the PAT has been made. Now let’s talk about the Keyhole section in more detail.
Keyhole apertures are definitely one of the harder sections of the PAT. You are given a 2D representation of a 3D object and are essentially asked to visualize it from different orthographic positions. In simpler terms, your task is to mentally visualize and manipulate the 3D object and orient it in a way which will allow it to perfectly fit into one of the keyhole/apertures shown as answer options. Think of the 3D object as the key and the answer choices as the keyholes as the name of the section would suggest. This key (3D object) can only fit into one of the keyholes. Here are the rules/guidelines you must abide by when completing this section:
- Before passing the object through the keyhole/aperture, you are allowed to mentally rotate and translate the object in any direction.
- Once the insertion of the 3D object in the keyhole has begun, you are not allowed to mentally rotate or translate the object anymore.
- Not only do keyholes (answer choices) have to be the correct shape, but they must also be the correct size.
- Hidden parts of the object are not subject to irregularities. However, if symmetry is shown or indicated, you must extend the symmetry to the hidden portion of the object as well.
You must get used to viewing the drawings in this section as they are, without making inferences about length and by paying close attention to proportional relationships. If you measure an edge from the 3D depiction in an aperture question and compare it to the same edge measurement taken from the correct orthographic answer choice, they will not always be identical due to perspective! Do not let this throw you off. Instead you must focus on the length of an edge in relation to a different edge on the same answer choice. When starting out, it is useful to first picture the orthographic side profile of the object in question before even looking at the answer choices.
The following is one approach that can be used to tackle this section. Understand that in reality, the process of doing these questions is not as robotic as this list will portray. With practice, this will become second nature and your mind will go through the steps naturally in the order in which you are most comfortable with.
- Quickly comprehend the object you are given in 3D and imagine how it will look orthographically from the three different positional views (Top/Bottom, Front/Back, Right/Left).
- Look at the answer choices that show the position you are most sure of and look for any irregularities that you did not expect.
- Eliminate answers as you cycle through the three different positional views.
- If more than one answer choice corresponds with one view (ex. Two answer choices both are showing a TOP view), rapidly shift your focus from one to another until you spot the difference.
- If more than one answer choice seems viable, pay close attention to the proportions and scaling of each choice.
And remember, the most important consideration in not only this section but the PAT in general is time. Do not lose yourself in a question. If you find yourself struggling to visualize an object or if you are dedicating a lot of time to one question, mark the question and move on. Simply taking a visual break from a tough question is advantageous. You are more likely to notice something you initially overlooked if you move on and let the object slip out of your short term memory. And finally, just like most things in life, practice makes perfect. So start right now and get ready to CRUSH the DAT!