There are three types of orthographic projection: isometric projection, dimetric projection, and trimetric projection. The difference between these 3 types is the angle measurement between directions, which also affects the scale of the object in the drawing.
Isometric Projection
An isometric projection shows all 3 dimensions of a figure in one drawing, and all directions are equally scaled. This is because "iso" means "equal" and "metric" means "measurement," so all three directions have equal measurement. An isometric projection is drawn using isometric axes, where the three axes are all 120 degrees apart. The drawing appears to show the object from a corner angle so that it appears to be in 3D, even though it is a two-dimensional drawing.
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Isometric projections are often used for furniture and structural design. It only requires one view of the object, shows the object's 3D representation, and the object can be drawn to scale. However, the appearance of the object can be distorted and it is not very useful for curved shapes. An example of an isometric projection of a cube is shown below.
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Dimetric Projection
A dimetric projection scales two directions equally and the other differently. For example, the x and y axes are 135 degrees apart and the y and z axes are 135 degrees apart in the image below. However, the x and z axes are only 90 degrees apart.
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Dimetric projections usually appear more realistic than isometric projections.
Trimetric Projection
In a trimetric projection, all three directions have different scales. Trimetric projections also usually appear more realistic than isometric projections.
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In an orthographic sketch, the 3 views are often arranged in a particular way. The front view is shown in the lower left, the top view is shown in the upper left, and the side view is shown in the lower right. Sometimes, the isometric drawing will be shown in the top right, but it does not have to be drawn to the same scale as the other 3 views. This is not always the case and the views are often labeled in the final orthographic drawing example.
Consider a three-dimensional L-shaped object. The image below shows this orthographic projection example. The L-shaped object is shown in blue and the three orthographic projections are shown in yellow. Notice that this is an isometric projection, because the three axes are all 120 degrees apart.
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The projection labeled "H" represents the top view. The projection labeled "L" represents the front view. The projection labeled "V" represents the side view. The next drawing shows the three orthographic views that represent the L-shaped object.
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Notice that there are lines representing where changes in depth occur in the object.
The next two images show another example of an orthographic projection of a house-shaped object. First, the isometric drawing is shown with the three orthographic projections:
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The following image shows the final orthographic sketch:
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An orthographic projection is a method for creating a two-dimensional representation of a three-dimensional object by projecting 3 different views of the object onto an orthogonal, or perpendicular, plane. The orthographic drawing usually includes 3 orthographic views: the front view, the side view (usually the right side), and the top view. An isometric drawing is a drawing of a three-dimensional object in 2 dimensions where the object is shown from a corner angle so that the front, side, and top are all visible at once.
In an orthographic drawing, the right side view of the object is usually shown in the lower right, the front view is usually shown in the lower left, and the top view is usually shown in the upper left. Orthographic projections are important, particularly in engineering, because they act as a universal language between designers and builders that they can both understand.
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Video Transcript
Orthographic Projection
Suppose you want someone in another country to design this triangular structure for you. You send them this picture, but it causes some confusion.
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Do they consider the green triangle to be in the front or the back of the structure? You don't speak their language, so you can't explain it to them. What do you do?
Thankfully, we have orthographic projections to help in situations like this. Put simply, an orthographic projection is a way of representing a three-dimensional object in two dimensions. It uses different two-dimensional views of the object instead of a single three-dimensional view. This allows you to communicate exactly what you want your structure to look like and eliminates any miscommunication between you and the person creating your design.
Different Views
Typically, an orthographic projection drawing consists of three different views: a front view, a top view, and a side view. Occasionally, more views are used for clarity. The side view is usually the right side, but if the left side is used, it is noted in the drawing.
To draw one of the views of an object, use lines to represent changes in depth. For example, consider this object with its right side view orthographic projection:
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Notice that there are lines where there are any depth changes in the structure; this changes the right side view of a three-dimensional object into a two-dimensional picture. These next two images show the front view and the top view of the same object:
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Measurements
In an actual orthographic projection, all of the views are included on the same page. Normally, the front view is in the lower left corner of the page, the top view is in the upper left corner, and the right side view is in the lower right corner. The same scale is used for all three of the drawings, and their lengths, widths, and heights are all lined up.
Sometimes, the isometric drawing of the object is included in the upper right corner. An isometric drawing is a view of an object from a corner angle so that all the different views of the object can be seen. Though an isometric drawing is two-dimensional, it appears three-dimensional. The isometric drawing need not be drawn to scale or lined up with the three orthographic projection drawings.
Often, an orthographic projection drawing includes measurements of the dimensions of each of the views. This allows the person creating the design to make it to scale as the designer wishes. This image shows the actual orthographic projection of the object shown earlier:
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Example
Let's consider another example. Suppose you want to build a set of steps that you can use to reach the top shelf of a cupboard. You know there are three steps, and you know how tall the steps need to be and the dimensions of each step. The only problem is that you can't build them yourself. The good news is that you can create an orthographic projection of your steps and present it to a builder, and they can build it for you based off your orthographic drawing shown in the image:
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In the image, we see that you want a set of steps that are each ten inches high, twelve inches deep, and 36 inches long. This shouldn't be too hard for the builder to make. You will have your set of steps in no time thanks to this drawing!
Lesson Summary
Orthographic projections are two-dimensional drawings of different views of a three-dimensional object. These projections serve as a sort of universal language when it comes to engineering and building, and allow for smooth communication between designer and builder as to what is expected.
An orthographic projection normally contains three views of the object: the front view in the lower left corner, the top view in the upper left corner, and the right side view in the lower right corner. The drawing often includes an isometric drawing of the object, which is a view of the object from an angle that shows all three of the different views. Measurements and dimensions are also normally included in the drawing. Orthographic projections are extremely important in mathematics, engineering, and the like, so it's great to be familiar with them.
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