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every picture states the point it is correct from
Series

Isocircle — the series

2 essays on one idea, from the one that introduces it to the one that assumes the rest.
  1. true ellipse — axis ratio 0.5774four arcs — 5.72% short along the major axisthe four tangent points are exactworst departure 5.72% of the semi-major axis

    The ellipse the drawing office draws

    Every isometric ellipse template is cut to a construction of four circular arcs, and every account of it calls the result an ellipse. It is not one and cannot be: a circular arc has constant curvature and a conic's varies, so the two can agree at four points and nowhere between. The four-centre curve reaches 2√2/3 of the true semi-major axis — 5.72% short — and its minor axis is 3.53% too long.

    part 4 · parallel
  2. the face's normal, drawnratio 0.8112 against the template's 0.5774tilt 0°major axis ⟂ the drawn normal

    A circle off the coordinate planes

    An ellipse template is cut at one ratio, and the ratio is the cosine of one angle: between a coordinate plane's normal and the direction of projection. A face tilted out of that plane needs a different ratio and — the half that gets drawn wrong even when the ratio is close — a major axis pointing somewhere else, perpendicular to the drawn normal rather than to any edge.

    part 5 · parallel

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