A heptagonal triangle is a non-isosceles triangle formed by three vertices of a regular heptagon. Its angles are π 7 , 2π 7 and 4π 7 . As such, there is a unique choice of a companion heptagonal triangle formed by three of the remaining four vertices. Given a heptagonal triangle, we display a number of interesting companion pairs of heptagonal triangles on its nine-point circle and Brocard circ...

Consider a triangle whose three vertices are grid points. Let k denote the number of grid points in the triangle. We describe an indexing of the triangle: a bijective mapping from f0;. .. ; k ?1g to the grid points in the triangle. Computing such a mapping is a fundamental subroutine in ne-grained parallel computation arising in graphics applications such as ray-tracing. We describe a very fast...

In this paper two improvements to speed up collision detection are described. Firstly, a method called oncollide sphere-tree, OCST for short, is presented. This approach works by detecting collisions among models with arbitrary geometry using the video card’s Graphics Processing Units, GPU. While candidate parts of colliding objects are being detected, the OCST is constructed for collision eval...

Triangles meshes are the most popular standard model used to represent polygonal surfaces in Computer Graphics. Drawing these meshes as a set of independent triangles involves sending a vast amount of information to the graphic engine. The use of primitives such as triangle fans and strips, which make use of the connectivity information between the triangles in the mesh, dramatically reduces th...

We present a method to produce a hierarchy of triangle meshes that can be used to blend different levels of detail in a smooth fashion. The algorithm produces a sequence of meshes 00, 01, 02, ..., 0n, where each mesh 0i can be transformed to mesh 0i+1 through a set of triangle-collapse operations. For each triangle, a function is generated that approximates the underlying surface in the area of...

Starting with any nondegenerate triangle we can use a well defined interior point of the triangle to subdivide it into six smaller triangles. We can repeat this process with each new triangle, and continue doing so over and over. We show that starting with any arbitrary triangle, the resulting set of triangles formed by this process contains triangles arbitrarily close (up to similarity) any gi...

X id → X → 0→ · For any morphism u : X → Y , there is an object Z (called a mapping cone of the morphism u) fitting into a distinguished triangle X u − → Y → Z → · Any triangle isomorphic to a distinguished triangle is distinguished. This means that if X u − → Y v − → Z w −→ X[1] is a distinguished triangle, and f : X → X, g : Y → Y , and h : Z → Z are isomorphisms, then X′ gu f −1 −−−−→ Y ′ hv...

A triangle in a triple system is a collection of three edges isomorphic to {123, 124, 345}. A triple system is triangle-free if it contains no three edges forming a triangle. It is tripartite if it has a vertex partition into three parts such that every edge has exactly one point in each part. It is easy to see that every tripartite triple system is triangle-free. We prove that almost all trian...

Starting with any nondegenerate triangle, we can use an interior point of the triangle to subdivide it into six smaller triangles. We can repeat this process with each new triangle, and continue doing so over and over. We show that starting with any arbitrary triangle, the resulting set of triangles formed by this process contains triangles arbitrarily close (up to similarity) to any given tria...

Complex hyperbolic triangle groups, originally studied by Mostow in building the first nonarithmetic lattices in PU(2, 1), are a natural generalization of the classical triangle groups. A theorem of Takeuchi states that there are only finitely many Fuchsian triangle groups that determine an arithmetic lattice in PSL2(R), so triangle groups are generically nonarithmetic. We prove similar finiten...