computational geometry and geometric shape matching
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Computational Geometry and Geometric Shape Matching. What is Computational Geometry?. Algorithms for geometric objects. Convex Hull. Given a set of pins on a pinboard And a rubber band around them How does the rubber band look when it snaps tight?. Convex Hull. - PowerPoint PPT PresentationTRANSCRIPT
Computational Geometry and Geometric Shape Matching
What is Computational Geometry?What is Computational Geometry? Algorithms for geometric objects
Convex HullConvex Hull Given a set of pins on a pinboard
And a rubber band around them
How does the rubber band look when it snaps tight?
Convex HullConvex Hull Given a set of pins on a pinboard
And a rubber band around them
How does the rubber band look when it snaps tight?
Voronoi DiagramVoronoi Diagram Given all post offices in San Antonio
Find a subdivision of San Antonio into cells such that points in a cell are all closest to one post office
Voronoi DiagramVoronoi Diagram Given all post offices in San Antonio
Find a subdivision of San Antonio into cells such that points in a cell are all closest to one post office
Security: Art GallerySecurity: Art Gallery Given an art gallery
How many guards do you need to guard the whole gallery? Where should they be located?
Data basesData bases Given a set of points (data sets) in high dimensional space
Preprocess them such that orthogonal range queries can be answered efficiently.
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects such as points
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects such as points line segments
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects such as points line segments triangles
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects such as
How similar are two geometric shapes?
points line segments triangles
Geometric Shape MatchingGeometric Shape Matching Consider geometric shapes to be composed of a number of basic objects such as
How similar are two geometric shapes?
points line segments triangles
Choice of distance measure Full or partial matching Exact or approximate matching Transformations (translations, rotations, scalings)
Computer-Aided NeurosurgeryComputer-Aided Neurosurgery
FU Berlin, Functional Imaging Technologies GmbH and the medical school ‘Benjamin Franklin’ at FU Berlin
BackgroundBackground Computer assisted neuro surgery (esp. brain tumor surgery)
BackgroundBackground Computer assisted neuro surgery (esp. brain tumor surgery) Before Surgery:
Functional MR scan of the brain
3D model of the brain
BackgroundBackground Computer assisted neuro surgery (esp. brain tumor surgery) Before Surgery:
Functional MR scan of the brain
3D model of the brain
During Surgery:
BackgroundBackground Computer assisted neuro surgery (esp. brain tumor surgery) Before Surgery:
Functional MR scan of the brain
3D model of the brain
During Surgery:
Electromagnetic pointing device
Display positions in 3D model
BackgroundBackground Computer assisted neuro surgery (esp. brain tumor surgery) Before Surgery:
Functional MR scan of the brain
3D model of the brain
During Surgery:
Electromagnetic pointing device
Display positions in 3D model
Navigation aid mapping positions in the brain to a prerecorded 3D MR image of the brain
Landmark Registration Landmark Registration Set of markers attached to patient’s head
3D model during surgeryimage world
Small but very noisy point sets
Find nearly rigid motion that maps image markers to world markers
Rigid Point MatchingRigid Point Matching P={p1,p2,…,pn} Q={q1,q2,…,qm} point sets in R3
P Q
Rigid Point MatchingRigid Point Matching P={p1,p2,…,pn} Q={q1,q2,…,qm} point sets in R3
P Q
Rigid matching maps edges with same length onto each other
Rigid Point MatchingRigid Point Matching P={p1,p2,…,pn} Q={q1,q2,…,qm} point sets in R3
P Q
Rigid matching maps edges with same length onto each other
Nearly rigid matching maps edges with similar lengths onto each other
Scoring TableScoring Table
Edges with similar lengths indicate a possible matching of and or vice versa
For each pair of similar edges,
increase the score of all pairs of
involved endpoints
pi
pj
qu qv
Maintain score for each pair
indicating the “quality” of matching
those two points
p1 pn
q1
qm
• • •
• • •
Scoring TableScoring Table
Edges with similar lengths indicate a possible matching of and or vice versa
Maintain score for each pair
indicating the “quality” of matching
those two points
For each pair of similar edges,
increase the score of all pairs of
involved endpoints
pi
pj
qu qv
p1 pi pj pn
q1
qu
qv
qm
Finding a TransformationFinding a Transformation Extract combinatorial matching
from scoring table
Least-Squares Approximation:
Find affine transformation A that minimizes the sum of the squared distances between corresponding points
Test if A is nearly rigid (check determinant, unit vector images, etc.)
Computer-Aided Neurosurgery: Computer-Aided Neurosurgery: SummarySummary
Direct linear algebra approaches were numerically very unstable
Geometric approach of splitting the problem into - finding the combinatorial matching and then- computing the nearly rigid transformation
is very easy to implement and proved to be very robust.
The algorithm is integrated into a commercial product and used in practice.
Protein Gel MatchingProtein Gel Matching
FU Berlin, UofA, German Heart Center Berlin
2D Gel Electrophoresis2D Gel Electrophoresis
Two-dimensional Gel Electrophoresis (2DE) is
an important method in proteome research
a high resolution technique which is capable to separate thousands of proteins from a tissue sample
2D Gel Electrophoresis2D Gel Electrophoresis
2D Gel Electrophoresis2D Gel Electrophoresis
Proteins are concentrated in so called spots of (axis- parallel) elliptic shape
2D Gel Electrophoresis2D Gel Electrophoresis
Proteins are concentrated in so called spots of (axis- parallel) elliptic shape
Protein analysis by mass spectrometry (expensive)
2D Gel Electrophoresis2D Gel Electrophoresis
2D Gel Electrophoresis2D Gel Electrophoresis
Gel Matching
Protein identification by gel image comparison is faster and not expensive
The Algorithmic ApproachThe Algorithmic Approach
Spot detection
Assign to each spot the coordinates of its center point and its intensity
Make use of ideas and methods from Computational Geometry:
Point pattern matching
Consider a gel as a point pattern. Then the problem reduces to a partial approximate point pattern matching.
GPS Curve LocationGPS Curve Location
FU Berlin and UofA and UTSA
Given:• A geometric graph G
(embedded in R2 with line segments)
• A polygonal curve
Task:Find a path in G that
is the most similar to
Finding a Curve in a MapFinding a Curve in a Map
Given:• A geometric graph G
(embedded in R2 with line segments)
• A polygonal curve
Task:Find a path in G that
is the most similar to
Finding a Curve in a MapFinding a Curve in a Map
• Consider :– A given roadmap, and– a sequence of GPS positions obtained from a person
travelling on some of the roads while recording her positioning information using a GPS receiver
polygonal curve
• Problem: – The noise of the GPS receiver distorts the polygonal curve
inherently
• Task: – Find the roads in the roadmap that have been traveled
Application: Map ConstructionApplication: Map Construction