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Computing and Processing Correspondences with Functional Maps
Maks Ovsjanikov, Etienne Corman, Michael Bronstein, Emanuele Rodolà, Mirela Ben‐Chen, Leonidas Guibas, Frederic Chazal, Alex Bronstein
SIGGRAPH 2017 course
Functional Vector Fields
Mirela Ben‐ChenTechnion, Israel Institute of Technology
ERC Project 714776 (OPREP)
So far
Computing and analyzing FMAPs Using FMAPs for function transfer
3[Ovsjanikov, BC, Solomon, Butscher, Guibas, SIGGRAPH 2012]
This part
Computing FMAPs using vector fields Using FMAPs for vector field transfer
4[Azencot, BC, Chazal, Ovsjanikov, SGP 2013]
What are vector fields?
• Smooth assignment of “arrow” per point
• Only tangent vector fields
• Visualize with texture• Can see direction but not length
5
Vector fields and maps – symbiosis
Fluid SimulationQuad remeshing Map ImprovementAzencot, Corman, BC, Ovsjanikov, SIGGRAPH 2017 Corman, Ovsjanikov, Chambolle, SGP 2015 Azencot, Vantzos, Wardetzky, Rumpf, BC, SCA 2015
Transporting data with point‐to‐point maps
Mapping scalars Mapping vectors
7
∈∈ ∈∈∈ ∈?
Tangent plane of at
The Map Differential
• Start a curve from with tangent
• Map the curve to
• is the tangent of the mapped curve at
8
∈∈
∈∈
Transporting data with point‐to‐point maps
Mapping scalars Mapping vectors
9
∈∈ ∈∈∈ ∈
Tangent plane of at
Transporting data with functional maps
Mapping functions Mapping vector fields
10
: → : →
The Map Differential
11
0
: 0,1 →
0
: 0,1 →
.5
1
.5
1
The functional Map Differential
12
0
: 0,1 →
0
: 0,1 →
.5
1
.5
1
The functional Map Differential
13
The functional Map Differential
14
: →
The functional Map Differential
15
: →: →
The functional Map Differential
16
: →: →
0 0′ 0 ⟨ , ⟩′ 0 ⟨ , ⟩
, ⟨ , ⟩
The functional Map Differential
Corresponding vector fields
18
For all
Corresponding vector fields
19
For all
Functional Vector Fields
20
LinearComplete*
Corresponding FVFs
21
, ⟨ , ⟩
Corresponding FVFs commute with FMap
22
Application – Joint vector field design
23constraints
smoothness
map consistency
Application – Joint vector field design
24constraints + smoothness + consistency
Application ‐ Joint Quad‐remeshing
25
Wed 9am, Room 152
[Azencot, Corman, BC, Ovsjanikov, SIGGRAPH 2017]
Map “animation”
27
∈∈
One map Map sequence
∈∈
1.5
0
A 1‐parameter family of maps
28
Back to vector fields
29
Back to vector fields, self maps
30.5 ∈
Back to vector fields, self maps
31∈
From maps to vector fields
32∈
,
From vector fields to trajectories
• We know: map → vector fields
• How to do: vector fields →map?
• Given solve for such that
33
The flow PDE
From vector fields to functional trajectories
• Given (stationary) , solve for such that
34
0 ∘
The flow:
The functional flow:
The functional flow
35
The functional flow
36
⟨ , ⟩
The discrete functional flow
• The surface is a triangle mesh
• The function is represented using a linear basis , e.g. hat basis
• is a vector, is a matrix
• A matrix ODE
37
The discrete functional flow
• A matrix ODE
• Closed form solution
38
Implementation
• Mesh : vertices, faces.• Represent in the hat basis ‐ ∈• Represent in the hat basis – a sparse matrix ∈
• Compute t expmv , ,
expmv: https://www.mathworks.com/matlabcentral/fileexchange/29576‐matrix‐exponential‐times‐a‐vector?focused=5172371&tab=function
Interpolate to vertices vector per face gradient operator
ApplicationsMaps from vector fields
40[Azencot, Vantzos, BC, SGP 2016]
ApplicationsIncompressible flow on surfaces• Numerically simulate the equation
• Vector field changes, more complicated• Total vorticity conserved by construction
41[Azencot, Weißmann, Ovsjanikov, Wardetzky, BC, SGP 2014]
ApplicationsIncompressible flow on surfaces
42
ApplicationsViscous thin films on surfaces
Total volume of fluid conserved by construction
43[Azencot, Vantzos, Wardetzky, Rumpf, BC, SCA 2015]
ApplicationsInferring vector fields
44
is distance preserving commutes with Δ
, , || Δ Δ ||
commutes with Δ
|| Δ Δ ||
[Azencot, BC, Chazal, Ovsjanikov, SGP 2013]
ApplicationsInferring vector fieldsis area preserving is orthogonal
is a rotation in functional space
is anti‐symmetric
is divergence free
(some) conclusions
• Vector fields and maps relate through tangents to trajectories
• Can be used to transport vector fields with maps orto compute maps from vector fields
• The functional approach allows to use linear algebra instead of geometric tracing for trajectory related problems
46
References
• Ovsjanikov, BC, Solomon, Butscher, Guibas, SIGGRAPH 2012, “Functional Maps: A Flexible Representation of Maps Between Shapes”
• Azencot, BC, Chazal, Ovsjanikov, SGP 2013, “An Operator Approach to Tangent Vector Field Processing”
• Azencot*, Weißmann*, Ovsjanikov, Wardetzky, BC, SGP 2014, “Functional Fluids on Surfaces”
• Corman, Ovsjanikov, Chambolle, SGP 2015, “Continuous Matching via Vector Field Flow”
• Azencot, Vantzos, Wardetzky, Rumpf, BC, SCA 2015, “Functional Thin Films on Surfaces”
• Azencot, Vantzos, BC, SGP 2016, “Advection‐Based Function Matching on Surfaces”
• Azencot, Corman, BC, Ovsjanikov, SIGGRAPH 2017, “Consistent Functional Cross Field Design for Mesh Quadrangulation”
47