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A branch of geometry dealing with convex sets and functions. Polytopes, convex bodies, discrete geometry, linear programming, antimatroids, ...

2 votes

Algorithm to find largest planar section of a convex polyhedral solid

Your Question 2 (max/min area/volume shadow version) is answered in this paper: McKenna, Michael, and Raimund Seidel. "Finding the optimal shadows of a convex polytope." In Proceedings 1st Annual Sym …
Joseph O'Rourke's user avatar
2 votes

To place copies of a planar convex region such that number of 'contacts' among them is maxim...

The left shape below has $3$ contacts (circled) "between pairs of units" and hull area $> 3$, while the right shape has $2$ contacts and area $3$. So minimizing the hull area does not always maximize …
Joseph O'Rourke's user avatar
5 votes

Finding points inside innermost convex hull

Here is an illustration of Gerry Myerson's nice idea: The left set has onion depth $n/3$, the right set, after small rotations, has depth 1. Incidentally, there is an efficient algorithm to find the …
The Amplitwist's user avatar
1 vote

On equipartitions of surfaces of 3D convex regions

Let $C$ be a cone with lateral side $A$ and base $B$. So $C = A \cup B$. The base is geodetically convex. But if I'm interpreting the definition correctly, $A$ is not geodetically convex: For any two …
Joseph O'Rourke's user avatar
2 votes

Distance from constant width bodies

Not an answer; just an illustration. I had some difficulty understanding the question, so... Here $n=2$, so the shapes are planar, $\mathbb{R}^2$. I used Reuleaux triangles for the $3=n{+}1$ unit-cons …
Martin Sleziak's user avatar
1 vote

Cone unfolding of space curves

Pardon me for this bit of self-promotion, especially because this is only tangential to the OP's concerns. But cone unrolling and Anton Petrunin's mention of Alexandrov's developments, in conjunction …
Joseph O'Rourke's user avatar
5 votes

Convex hull of a variety in real space

These references may help? Or at least lead you to related literature. João Gouveia and Rekha Thomas. "Convex hulls of algebraic sets." In Handbook on Semidefinite, Conic and Polynomial Optimization, …
Rodrigo de Azevedo's user avatar
1 vote

Smallest 3-ellipses that contain triangles

My answer here may help, especially the citation to Nie, Jiawang, Pablo A. Parrilo, and Bernd Sturmfels. "Semidefinite representation of the $k$-ellipse." In Algorithms in Algebraic Geometry, pp. 117 …
Joseph O'Rourke's user avatar
2 votes

On intersections of several convex regions

Addressing the OP's "Note," as far as I know, this is the algorithm status: There are fast approximation algorithms, but I have not found an exact algorithm (except when only translations are permitte …
Joseph O'Rourke's user avatar
3 votes

On some centers of convex regions based on partitions

Let me just quickly remark on one embedded question (but not your main questions): "then it could be called the 'area partition center' of the region and finding this center for a general given regio …
Joseph O'Rourke's user avatar
3 votes
Accepted

Projection of convex set onto a convex set

I believe this answers (1). $P$ is the pyramid illustrated. $S$ is a square resting on the apex of $P$, at height $z_1$. Projecting $S$ down (green lines) onto $P$ results in the nonconvex shape outli …
Joseph O'Rourke's user avatar
2 votes

On 'fair bisectors' of planar convex regions

This is not an answer, and not even that helpful, but I wanted to see the central pattern formed by the collection of perimeter bisectors.                    
Joseph O'Rourke's user avatar
3 votes

Number of regions formed by $n$ points in general position

Perhaps it is worth quoting this theorem, even though it does not distinguish bounded from unbounded cells, and is phrased in terms of the number of hyperplanes rather than the number of points determ …
Joseph O'Rourke's user avatar
1 vote
Accepted

Smallest triangles that contain 2D convex regions with reflection symmetry

The example below seems to suggest No for the inscribed question as well. The line of symmetry is horizontal (dashed). It seems the best aligned isosceles triangle (pink) has area $A_1=\frac{1}{2} ( …
Joseph O'Rourke's user avatar
5 votes

Convex hull in a discrete space

There is a notion called the "orthogonal convex hull," or the "digital convex hull," which may be what you seek. For example, in this paper, Karmakar, Nilanjana, and Arindam Biswas. "Construction …
Joseph O'Rourke's user avatar

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