John K. Johnstone

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In general, two quadric surface intersect in a space quartic curve. However, the intersection frequently degenerates to a collection of plane curves. Degenerate cases are frequent in geometric/solid modeling because degeneracies are often required by design. Their detection is important because degenerate intersections can be computed more easily and allow(More)
We develop an efficient algorithm for the construction of common tangents between a set of Bezier curves. Common tangents are important in visibility, lighting, robot motion, and convex hulls. Common tangency is reduced to the intersection of parametric curves in a dual space, rather than the traditional intersection of implicit curves. We show how to(More)
We present a local method for the computation of the intersections of plane algebraic curve segments. The conventional method of intersection is global, because it must first find all of the intersections between two curves before it can restrict the segments in question; hence, it cannot take advantage of situations dealing with the intersection of(More)
PURPOSE This study explores variation in the axial location of Bruch's membrane opening (BMO) to determine if this reference plane varies with age and race. METHODS There were 168 spectral-domain optical coherence tomography (SDOCT) optic nerve head volumes that were obtained from healthy subjects and manually delineated within 24 axial slices to develop(More)
We present a method for constructing tensor product Bezier surfaces from contour (cross-section) data. Minimal area triangulations are used to guide the surface construction, and the final surface reflects the optimality of the triangulation. The resulting surface differs from the initial triangulation in two important ways: it is smooth (as opposed to the(More)