Drawing a 3D isometric circle actually involves drawing an ellipse, as a circle viewed in isometric projection appears elongated. The most common and straightforward manual method uses four arcs within an isometric square (a rhombus) to approximate the ellipse.
Understanding Isometric Circles
In isometric projection, all three axes (width, depth, height) are shown equally foreshortened, and the angles between them are 120 degrees. A circle parallel to one of the isometric planes (top, front, or side) is projected as an ellipse. The shape and orientation of this ellipse depend on which plane the circle lies on.
Step-by-Step 4-Center Method
This technique constructs the ellipse using four arcs drawn from four different centers.
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Start with the Isometric Square (Rhombus)
- First, draw the isometric square that the circle would fit inside. This rhombus will be oriented according to the plane the circle is on (e.g., for a circle on the top plane, the rhombus will have two sides at 30° to the horizontal).
- The sides of this rhombus will be equal to the diameter of your desired circle.
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Locate the Centers
- Find the midpoints of all four sides of the rhombus.
- From the two corners with the obtuse angle (the wider angles), draw a line connecting the corner to the midpoints of the opposite sides. These two corners are centers for the smaller arcs.
- Find the point where these lines intersect. There will be two such intersection points. These are the centers for the larger arcs.
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Draw the Arcs
- Using a compass or ellipse template:
- From the two obtuse-angle corners, draw the smaller arcs connecting the midpoints of the two adjacent sides.
- From the two intersection points (the centers for the larger arcs), draw the larger arcs connecting the midpoints where the smaller arcs end.
- According to drawing techniques like the one described in the reference, you can draw in your first arc, typically one of the larger arcs.
- Crucially, the same radius should work for the bottom arc as well. These two larger arcs share the same radius.
- One double check it is essential before you draw it to ensure the radius correctly connects the points. The radii for the two smaller arcs (from the obtuse corners) will also be the same as each other, but different from the larger arcs.
- Using a compass or ellipse template:
By drawing these four connected arcs, you create a close and visually accurate approximation of an isometric ellipse, representing your 3D isometric circle.
