Uniform edge lengths are a reasonable proxy for mesh quality, since equilateral triangles have good angles. But if you have more specific criteria, you can usually do better. "Hodge-Optimized Triangulations" provides a nice discussion of this perspective: geometry.caltech.edu/pubs/MMdGD11.p…
A popular approach in graphics is something like Botsch & Kobbelt, "Remeshing for Multiresolution Modeling" (Sec. 4): graphics.rwth-aachen.de/media/papers/r…

Basic idea: iteratively move vertices to equalize areas, split long edges, collapse short edges, & flip edges to improve vertex valence.
In this class of algorithms, I really like Chen & Holst, "Efficient mesh optimization schemes based on Optimal Delaunay Triangulations": math.uci.edu/~chenlong/Pape…

Here there's a clear notion of optimality, & an efficient preconditioner. For surfaces: restrict to tangential motions
Another classic is Alliez et al, "Isotropic Surface Remeshing": hal.inria.fr/inria-00071991…

Here the idea is to parameterize the mesh & nicely sample according to varying density in the plane. I don't sense this idea is used too much these days, due to the need to parameterize.
Though on second thought, there are methods that use sophisticated field-aligned parameterization to get very high-quality almost-regular meshes with few irregular vertices, such as Nieser et al, "Hexagonal Global Parameterization of Arbitrary Surfaces": mi.fu-berlin.de/en/math/groups…
More recently a popular tool is the award-winning "Instant Meshes" by @wenzeljakob et al: igl.ethz.ch/projects/insta…

Combines the strengths of field-aligned & local iterative methods to get extreme performance/scalability, albeit with more irregular vertices than, say, Nieser et al
Finally, a fun example where meshes with unit edge lengths show up is in Isenberg et al, "Connectivity Shapes": cs.unc.edu/~isenburg/rese…

The idea: if you have perfect unit edge lengths, you can throw away vertex positions and recover the geometry *purely* from the connectivity!
In simulation, the award-winning "El Topo" package of Brochu & Bridson uses near-unit edge lengths to provide high-quality free surface tracking: github.com/tysonbrochu/el…

(By the way, "award winning" in these posts refers to the SGP software award @GeometryProcess!)
@BrunoLevy01 has a great package called GEOGRAM that provides a lot of great regular meshing functionality: alice.loria.fr/software/geogr…

Bruno will be able to give better details about the algorithms used, and interesting applications like optimal transport that I didn't mention yet.
It's also important to mention that uniform edge lengths provide more detail than necessary in large regions with low curvature.

Other methods adapt to local curvature/feature size, like Dunyach et al, "Adaptive Remeshing for Real-Time Mesh Deformation": hal.archives-ouvertes.fr/hal-01295339/d…
Likewise, the Holst & Chen paper mentioned earlier allows spatial adaptivity, by providing a density function: math.uci.edu/~chenlong/Pape…
There are sure to be countless references I'm missing both to algorithms & applications—but that should provide a few useful pointers!

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Keenan Crane

Keenan Crane Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @keenanisalive

25 May
Excited to share a new #SIGGRAPH2021 paper with @markgillesie81 and Boris Springborn that is a pretty big breakthrough in mesh parameterization: cs.cmu.edu/~kmcrane/Proje…

In short: no matter how awful your mesh is, we compute beautiful high-quality texture coordinates.

(1/n) Image
For instance, just as a stress test we can try to flatten this crazy #Thingi10k model as a single piece, rather than cutting it up into many charts. We still get excellent texture coordinates, with no flipped triangles, no angle distortion, and little scale distortion.

(2/n)
In general, the algorithm is guaranteed to produce maps that do not locally fold over and are perfectly conformal in a discrete sense, for absolutely any triangle mesh. It also gives globally 1-to-1 maps to the sphere, and handles any configuration of "cone singularities" (3/n) Image
Read 13 tweets
11 May
1/n This past weekend I gave two lectures @HarvardCMSA on “intrinsic triangulations” and how they can open new doors in geometric computing.

Videos here:



And details about the (terrific!) event here: cmsa.fas.harvard.edu/frg-2021/
2/n The story begins with the transition in the 19th century from thinking about geometry in terms of points in space (extrinsic) to thinking about the broader ways we can describe shapes without knowing how they’re embedded (intrinsic).
3/n Even though the intrinsic picture is now commonplace in mathematics, it’s still not how most people think about mesh processing. Almost universally we still describe the geometry of a mesh using Cartesian coordinates in a global coordinate system—just as we did in the 19th c.
Read 19 tweets
3 Jul 20
Excited to share new work w/ @nmwsharp on a Laplace operator that works great for both point clouds and arbitrary, nonmanifold triangle meshes—aimed at geometry processing & learning:

web: cs.cmu.edu/~kmcrane/Proje…
code: github.com/nmwsharp/nonma…
video: youtube.com/watch?v=JY0koz…
(1/n) Image
First of all, if you don't know what a Laplace operator is or why it's important (and are curious to find out!), I've recorded an intro lecture here with a bunch of animations and examples:

youtube.com/watch?v=oEq9RO…

(2/n)
Just like the Fast Fourier Transform (FFT) is the foundation of a lot of classical signal processing, the Laplacian is the foundation for a lot of modern algorithms in geometry processing and geometric learning:

cs.cmu.edu/~kmcrane/Proje…

(3/n) Image
Read 16 tweets
6 May 20
Very excited to share #SIGGRAPH2020 paper w/ @rohansawhney1 on "Monte Carlo Geometry Processing"

cs.cmu.edu/~kmcrane/Proje…

We reimagine geometric algorithms without mesh generation or linear solves. Basically "ray tracing for geometry"—and that analogy goes pretty deep (1/n)
Especially for problems with super complicated geometry, not having to mesh the domain provides a massive reduction in real world end-to-end cost. For instance, this model takes 14 hours to mesh and solve w/ FEM, but less than 1 minute to preview with Monte Carlo: (2/n)
As an added bonus, we can do geometry processing directly on nonmanifold meshes, implicit surfaces, instanced geometry, CSG, Bezier curves, NURBS surfaces, etc., without doing any tessellation, sampling, mesh booleans, etc. So how does this all work? Here's the story. (3/n)
Read 22 tweets
11 Apr 20
Just uploaded a video on the Laplacian:

If you've heard of the Laplacian and always wondered what it was, or feel like you don't have great intuition for what it means, take a look—we explore how the Laplacian shows up in geometry, physics, & computation.
This video is part of a series of lectures on #DiscreteDifferentialGeometry from Carnegie Mellon University @SCSatCMU.

You can find the playlist here: youtube.com/playlist?list=…

The course webpage, including notes & exercises can be found here:
geometry.cs.cmu.edu/ddg
This lecture grew from a course at the terrific Symposium on Geometry Processing graduate school @GeometryProcess. You can find the whole list of videos here: school.geometryprocessing.org
Read 4 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Too expensive? Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal Become our Patreon

Thank you for your support!

Follow Us on Twitter!

:(