Reporting Status or Progress

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3D Modeling of Historic Sites Using Range and
Image Data
Peter Allen, Ioannis Stamos,Alejandro Troccoli,
Ben Smith, Marius Leordeanu, Y.C. Hsu Dept. of
Computer Science, Columbia University Dept. of
Computer Science, Hunter College, CUNY
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Preserving Cultural Heritage Sites

• Sites are subject to erosion, wear, vandalism
• Moving targets many phases of construction,
  damage and repair over many years
• Need to track changes, foresee structural
  problems
• Modeling allows a wider audience to virtually
  see and tour these sites
• Our Focus methods that can reduce modeling time
  using automatic methods

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Cathedral St. Pierre, Beauvais, France
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• Modeling the Cathedral
• Goals
• Cathedral on the World Monuments Fund's Most
  Endangered List.
• Create 3-D model to examine weaknesses in the
  building and proposed remedies
• Establish baseline for condition of Cathedral
• Visualize the building in previous contexts
• Basis for a new collaborative way of teaching
  about historic sites, in the classroom and on the
  Internet.

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History 1200 - 1600

• Commissioned in 1225 by Bishop Milon de Nanteuil
• Only the choir and transepts were completed -
  choir in 1272
• In 1284 part of the central vault collapsed
• Area where the nave and façade would be is still
  occupied by the previous church constructed just
  before 1000.
• Completed in 16th century, the transept was
  crowned by an ambitious central spire that
  allowed the cathedral to rival its counterpart in
  Rome.
• The tower collapsed on Ascension Day in 1573.

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Rendition of original central spire
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History 20th Century

• Cathedral survived intense incendiary bombing
  that destroyed much of Beauvais in WW II.
• Between 1950-80 many critical iron ties were
  removed from the choir buttresses in a damaging
  experiment.
• Temporary tie-and-brace system installed in the
  1990s may have made the cathedral too rigid,
  increasing rather than decreasing stresses upon
  it.
• There continues to be a lack of consensus on how
  to conserve the essential visual and structural
  integrity of this Gothic wonder.

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Problems with the Structure

• Wind Oscillation from English Channel winds
• Strange inner and outer aisle construction can
  cause rotational moments in the structure
• Leaking Roof, foundation is settling
• Built in 3 campaigns over hundreds of years with
  differing attention to detail

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Time-Lapse Image - Spire Movement Due to Wind
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Technical Challenges

• Create Global and coherent geometric models
  handle full range of geometries
• Reducing data complexity
• Registration of MANY million point data sets
• Range and intensity image fusion

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Beauvais Cathedral Exterior Scanning Session
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Beauvais Cathedral Interior
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Beauvais Cathedral Interior Scanning Session
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Exterior Raw Range Scan
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Beauvais Scan Detail
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Range Registration

• 3 Step Process
• Pairwise registration between overlapping scans.
  Match 3D lines in overlapping range images.
• Global registration using graph search to align
  all scans together.
• Multi-scan simultaneous ICP registration
  algorithm (Nishino et. al.)
• Produces accurate registration.

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Segmentation Algorithm

• Creates reduced data sets (80).
• Fit local plane to neighborhood of range points.
• Classify range points planar, non-planar,
  unknown.
• Merge into connected clusters of co-planar
  points.
• Identify boundaries of planes.
• Used to find prominent linear features for
  matching.

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Local Planarity Comparison
N
N
1
2
P
P
1
2
R
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Patches fit around points P1 and P2

• P1 and P2 are coplanar if
• acos (N1 . N2) lt angle
  threshold
• dmax(R12 N1, R12 N2) lt distance threshold

-1
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Segmentation and 3-D Registration Lines
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Pairwise Registration of Scans Overview

• Segmenter creates planes and associated boundary
  lines
• Matching lines in 2 scans can be problematic
• Attributes of lines serve as a good filter for
  matching lines length of lines, area of planar
  region that line bounds
• Use pairs of matched lines to compute transform
• Transform each line in one scan to the other.
  Results are graded by metric of number of matched
  lines after transform
• Choose best graded transform

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Pairwise Registration
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Registered Scans Beauvais Cathedral
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Global Registration
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• Graph Search Global Registration
• Create weighted graph of scans. Edges of graph
  are confidence in finding correct registration
  between pairs of scans
• Confidence (cost) is number of correctly aligned
  lines after applying registration (R,T)
• Global Registration find max-cost path from
  pivot scan to each scan

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Final ICP Registration
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Beauvais Cathedral Model Fly-Thru
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Inside-Out Beauvais Cathedral
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Texture Mapped Models
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Texture Mapped Models
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Texture Mapped Models
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Automating the Process
Build a Mobile Site Modeling Robot

• Robot can serve as a sensor platform containing
  ranging and imaging devices
• Onboard sensors can register sensor data with the
  environment GPS, Odom., Vision
• Given a 2-D map of an environment, robot can
  augment 2-D map with 3-D models
• Planner can interact with robot navigator to move
  to new viewing sites

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The AVENUE Mobile Platform
GPS
UTONOMOUS
Scanner
DGPS
EHICLE FOR
Network
XPLORATION AND
AVENUE
Camera
PTU
AVIGATION IN
Compass
Sonars
RBAN
PC
NVIRONMENTS
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Future Work

• Continue to automate the model building process
• Real-time texture mapping for realistic
  walk-throughs
• View planning finding the right viewpoints and
  number of views
• Incorporate sensor planning with robot path
  planning to plan next view
• Modeling with non-planar segments.
• Merging multiple overlapping photos.