Introduction to Orthographic Projection

TL;DR

Orthographic projection is a way to represent 3D objects in 2D by showing different views. You'll typically draw a front view, a top view (plan), and a side view (elevation) to fully describe an object. These views are aligned and scaled correctly, giving you a complete picture without perspective distortion.

1. The Mental Model

Imagine you're looking directly at an object from the front, then directly from above, and then directly from the side. Orthographic projection is simply drawing exactly what you see from each of those precise, straight-on viewpoints, as if you're flattening the object onto a piece of paper.

2. The Core Material

Orthographic projection is fundamental in design, engineering, and architecture. It allows you to communicate the exact shape and size of a 3D object on a 2D surface. Instead of a single perspective drawing, which can be misleading about true dimensions, you use multiple flat views.

2.1 The Three Main Views

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You'll generally create three primary views:

• Front Elevation: What you see when looking straight at the front of the object. This often shows the most characteristic features.
• Plan View (Top View): What you see when looking straight down on the object from above.
• Side Elevation: What you see when looking straight at one side of the object. This is usually either the left or right side, but sometimes both are needed.

The key is that each view is drawn as if your eye is infinitely far away, looking perfectly perpendicular to the object's surface. This means parallel lines on the object remain parallel in the drawing, and there's no foreshortening (things appearing smaller as they get further away).

2.2 Alignment and Consistency

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The different views aren't drawn randomly. They are always aligned with each other. This alignment is crucial:

• The front elevation and plan view share the same width. Features at the front of the object will align vertically between these two views.
• The front elevation and side elevation share the same height. Features at the top or bottom of the object will align horizontally between these two views.
• The plan view and side elevation relate through depth. A common method to transfer depths is using a 45-degree projection line or a compass arc.

Here’s how these views relate to each other:

graph TD
    A["3D Object"] --> B["View from Front"]
    A --> C["View from Top"]
    A --> D["View from Side (e.g., Right)"]

    B -- "Shares Width" --> C
    B -- "Shares Height" --> D
    C -- "Shares Depth (via 45-deg line)" --> D

2.3 Hidden Detail

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Not all lines will be visible from a given view. When a feature exists but is hidden behind another part of the object, you represent it using a dashed line (or hidden detail line). This is important for fully understanding the object's internal structure or obscured features.

2.4 Scale

All views must be drawn to the same scale. If you're drawing a house, you might use 1:100 scale; if it's a small mechanical part, 1:1 scale might be appropriate. Consistency is key.

3. Worked Example

Let's imagine a simple "L-shaped" block. It's 50mm long, 40mm wide, and 30mm high. One arm of the 'L' is 20mm wide and runs the full length, while the other arm is 20mm wide and runs the full width.

Here's how you'd typically lay out the views:

1. Front Elevation:
If you look at the 'L' from the front (the long part of the L facing you), you'd see a rectangle that's 50mm wide and 30mm high. Then, you'd see the cut-out shape within it.
* Draw a rectangle 50mm wide and 30mm high.
* From the right side, measure 20mm in (the width of the 'vertical' part of the L) and draw a vertical line up 10mm (30mm total height - 20mm of the bottom part).
* From that point, draw a horizontal line 30mm to the left (50mm total width - 20mm of the 'horizontal' part of the L). This completes the 'L' shape you see from the front.

2. Plan View (Top View):
Now look from above. You'll see the top surface of the 'L'.
* Directly below the front elevation, align the left and right edges.
* The total width will be 50mm (same as front elevation).
* The total depth will be 40mm.
* From the top-left, draw a rectangle 50mm wide and 20mm deep (the top of the horizontal arm).
* Then, from the left edge, draw another rectangle 20mm wide and 40mm deep (the top of the vertical arm). The overlapping part will create the 'L' shape.

3. Right Side Elevation:
Look at the object from the right side.
* Align the bottom and top heights with the front elevation. The total height is 30mm.
* The total depth will be 40mm (same as the plan view's depth).
* You'll see a rectangle that's 40mm deep and 20mm high (the bottom part of the L).
* Then, from the left edge of this view, you'll see a 20mm wide, 20mm deep, and 30mm high rectangle. This forms the side view.
* You would also see a hidden line for the top part of the 'L' that extends back.

All these views would be precisely aligned on your drawing paper, typically with the plan view below the front elevation, and the side elevation to the right of the front elevation.

4. Key Takeaways

• Orthographic projection uses multiple 2D views to fully describe a 3D object.
• The three main views are Front Elevation, Plan View (Top), and Side Elevation.
• Views are always drawn perpendicular to the object's surfaces, avoiding perspective distortion.
• All views must be precisely aligned with each other, sharing common dimensions (width, height, depth).
• Hidden features are represented using dashed lines to ensure a complete understanding of the object.
• All drawings in an orthographic set must be drawn to the same consistent scale.
• Orthographic projection is crucial for communicating exact dimensions and shapes in technical drawings.

Common Mistakes to Avoid:
- Not aligning the views properly, making it hard to interpret the object's true form.
- Forgetting to draw hidden lines, which leaves out important details.
- Drawing different views to different scales, leading to incorrect assumptions about dimensions.
- Adding perspective or drawing objects "as you see them" instead of strictly perpendicular.

5. Now Try It

Find a simple everyday object, like a small box, a book, or a stapler. On a piece of paper, try to draw its front elevation, plan view, and right-side elevation. Use a ruler to ensure your lines are straight and that the views are properly aligned (e.g., the width of your front view should match the width of your plan view). Don't worry about perfect hidden lines just yet, but try to identify where they might be needed. Success looks like having three distinct, aligned drawings that accurately represent the object from each cardinal direction without any perspective.