OpenARK — Tackling AR Challenges via Open- Source...
Transcript of OpenARK — Tackling AR Challenges via Open- Source...
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OpenARK — Tackling AR Challenges via Open-Source Development Kit
Allen Y. Yang
withLuisa Caldas, Mohammad Keshavarzi, Woojin Ko,
Joe Menke
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Organizers
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OpenARK Team
Students
• Oladapo Afolabi
• Adam Chang
• Alex Yu
• Bill Zhou
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Faculty
• Luisa Caldas
• Shankar Sastry
GitHub: https://github.com/augcog/OpenARK
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Slides available: vivecenter.berkeley.edu
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Princess Leia’s Hologram:First asynchronous telepresence
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Multi-User Interaction Demo: Microsoft Holoportation
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Multi-User AR Applications: Model, Share, Manipulate
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Office Hospital
Living Room
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3D Modeling for Personal AR Products
• Infer 3D using minimal number of images
• Accurate dense reconstruction for virtual augmentation
• Complete without holes
• Sharable and editable space models for multi-users
• Augmentation of human users as realistic avatars
• **Privacy and standards
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Solutions for Future AR Experience
1. Modeling Background Layout
2. Modeling Foreground Objects
3. Modeling User Avatars
4. Optimization & Sharing in Mutual Space
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Outline of the OpenARK Tutorial
• Session I: Contexture 3D Scene and Avatar Modeling
• Session II: 3D Reconstruction, SLAM, and Gesture Recognition
• Session III: Maximization and Manipulation of Contextual Mutual Space Models
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Traditional 3D Vision — “Building Rome on a (cloudless) day”
* Jan-Michael Frahm, et al. 2010
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Pros and Cons of SfM
Pros
• Widelyavailablehardware
• Unlimitedrange
• Uniformnoisemodel(Gaussian)
• Retainsurfacetexture
Cons
• Computationallyintensiveto
recover3Ddepth
• Doesn’tworkindark
• Doesn’tworkwhenlackof
texture
• Leadtoonlysparsegeometry
vs.dense3Dmap
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Anatomy of an AR platform
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Using Depth Camera to Scan Spaces
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Depth Cameras
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Depth from Single Camera
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TimeofFlight
StructuredLight
A
s
b
z1
z0
Blur:
DepthfromDefocus
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Depth from Stereo vs Time of Flight
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Depth from Stereo vs Time of Flight
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Basic ToF Principles
https://en.wikipedia.org/wiki/Time-of-flight_camera
Limitation:t_Dmustbesmallerthant
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Spatial Structured Light Approach
Projector
Camera
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Disparity from calibrated patterns
• Assumeareferencedisparity
Projector Camera
• Compute
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Pros and Cons of (most) Depth Cameras
Pros
• Computationallysimpler(using
lightreflectionandlook-up
tables)
• Workinthedark
• Workontexture-lesssurfaces
• Fulldense3DmapforAR/VR
Cons
• Lightemittermayconsumer
morepower
• Challengewithsunlight
• Unevennoisemodelindepth
• Costmoretomanufacture
emitterandsensor
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Available RGB-D Databases
• Indoor LIDAR-RGBD Scan: 5 models
• Matterport 3D: 90 scenes
• ScanNet (Structure): 707 spaces
• Gibson (Matterport): 572 buildings
• ShapeNet (CAD): 51,300 models
• PanoContext (panoramic): 700 Panoramas
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Berkeley ATLAS— Multi-resolution database for geometric super resolution
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• Cross-reference ground-truth LIDAR data with consumer-grade depth camera data (RealSense) for one-to-one correspondences
• PX-80 LIDAR (construction grade)
• RealSense D435i (consumer grade)
• PointGrey stereo cameras
• Technical challenges
• Multi-sensor synchronization (Arduino)
• Multi-sensor calibration (manually)
• Multi-sensor SLAM (OpenARK)
• 3D labeling (Python CV toolkit)
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A CV-assisted 3D labeling system
• Background room surfaces are first separated by clicking 3 points to define a surface
• Foreground objects are automatically bounded. We then label their categories
• Establish correspondence between LIDAR, RealSense, and images
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Bottleneck in 3D Objects via Point Cloud
• Usually obtain an incomplete model of objects from RGB-D sensors.
• Due to noise, occlusions, or material properties
• Task: Complete the 3D objects for accurate virtual augmentation
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Approach: Deformable CAD Models
• Propose to use deformable CAD model
• Match observation (data) while being geometrically complete
• Also solve for optimal scale and rigid body transformation in addition
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ShapeNet CAD Models
• ShapeNet [ Chang et al. arXiv 2015] is a richly annotated large scale dataset of 3D shapes.
• Models are normalized to unit cube, so need to be scaled and rigidly transformed.
• Provides annotations for:
• upright, front direction
• parts information
• Symmetry etc.
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3D Shape Completion
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hmin
h| f(h) − x |f(h)
latent
variable
x
• Auto-encoder network to estimate latent representation of the deformed CAD model space, which minimizes approximation error
* Achlioptas, Panos, et al. "Learning representations and generative models for 3D point
clouds." arXiv preprint arXiv:1707.02392, 2017.
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Approach I: Auto-Encoder (AE)
• Estimation error created via point clouds
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Original CAD Object Point Cloud Deformed CAD
+
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• Point Cloud: an object is sampled by N 3D points
S is an N-by-3 matrix
• Challenges with point clouds
1. Point Cloud sample are ambiguous and not unique
2. A set of 3D points are not ordered (compared to images and videos)
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AE Representation for 3D Point Clouds
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Auto-Encoder (AE) Objective
• A deep-learning architecture that learns to reproduce its input with most informative representation
• h is called the latent code for representing a family of input data
• Goal: Minimize reconstruction error
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Applications of AE on Point Cloud
• Changing appearance
• Point-cloud completion
• Classification based on h (when trained on all categories)
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* Achlioptas, Panos, et al. "Learning representations and generative models for 3D point
clouds." arXiv preprint arXiv:1707.02392, 2017.
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Drawback from AE Representation in Dense Shape Completion
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• Resulting point cloud minimizes the estimation error
• However, deformed mesh model may not be contextually plausible or visually appealing
• Generation of new shape is only related to the decoder part, but not the encoder
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Approach II
• Auto-Decoder Network
• Continuous signed distance function
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z f(x, z)
latent
variable
minz ∑
x
| f(x, z) − y |
[2] Park, Jeong Joon, et al. “DeepSDF” CVPR, 2019.
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Signed Distance Function
• SDF with respect to a set
where is the boundary of the set
• SDF is a continuous function
• Magnitude of is always unit (1)
• On the boundary, is equal to the normal vector
Ω
f(x) = {−d(x, ∂Ω) if x ∈ Ω
d(x, ∂Ω) if x ∈ Ωc
∂Ω
∇f(x)
∇f(x)
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Auto-Decoder (AD) Network
• Auto-Decoder Network
• How to inference optimal code
• Training: assume each code corresponds to
one shape
• Testing:
{z1, …, zN}
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[2] Park, Jeong Joon, et al. “DeepSDF” CVPR, 2019.
h
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Shape Completion
• Shape Completion Problem under AD Network
Finding the optimal given trained shape parameters and
partial observations
• The network can approximate any number of points, un-ordered.
• (x, y, z) can be any 3D point, so AD encodes continuous SDF.
• No encoder part is needed, therefore the main motivation to ignore during training.
z* θ
{x1, …, xK}
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Results with Improvements (ongoing)
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3D Avatar Modeling
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Skeletal Fully Articulated Deformable
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3D Avatar Modeling
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Deformable
1. Photo-realistic video games
2. Social media
3. Telepresence
4. Human simulations
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Existing Literature: Single-Camera Avatar Modeling
• Template-based: Using body skeleton/silhouette
• Vlasic et al., 2008
• Taylor et al., 2012
• OpenPose: Zhe Cao, et al, 2018
• Model-based: SMPL, SCAPE, …
• BodyFusion: T. Yu, et al., 2017
• DoubleFusion: Tao Yu, et al., 2018
• Delta: Federica Bogo, et al., 2015
• Free form: Static vs Dynamic
• KinectFusion: ISMAR 2011
• DynamicFusion: CVPR 2015
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Our Approach
Low Dimensional
ModelIncreasing robustness and speed by working in a low-dimensional
space.
Fast SolverTowards high
performance on low-compute devices.
Model FusionCombining 3D
Depth + 2D RGB information for
enhanced realism and robust tracking.
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OpenARK Avatar Open-Source Library
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Fusion of Multiple 3D Cues
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ICP Error
Physical model
Joint Prior
Neural network model
Pose Prior
Probabilistic model
based on human
knowledge
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Observed Point
Nearest neighbor
on SMPL model
to observed point
Iterative Closest Point (ICP) ErrorSum squared distance from observed body to modeled body
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Joint Position
Predicted by
Neural Net
Joint Position on
SMPL Model
Joint Prior
Sum squared distance from CNN joint positions to model
joint positions
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Parameterized by
Joint Pose
Weights Trained
from CMU MoCap
Dataset
Pose Prior
Likelihood of modeled pose being real human pose
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OpenPose as skeleton anchor
50* Zhe Cao, et al. OpenPose: Realtime multi-person 2D pose estimation using part
affinity fields, 2018
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Fit Pose
Fit Pose
New Frame
ICP Sanity
Check
Basic Process
GitHub: https://github.com/augcog/OpenARK