Localization in indoor environments by querying omnidirectional visual maps using perspective images...
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Localization in indoor environments by querying omnidirectional visual maps using perspective images Miguel Lourenco, V. Pedro and João P. Barreto ICRA
Localization in indoor environments by querying omnidirectional
visual maps using perspective images Miguel Lourenco, V. Pedro and
Joo P. Barreto ICRA 2012
Slide 2
Standard Image-based Indoor Localization (1/3) How can a robot
equipped with standard camera perform indoor localization? Miguel
Loureno Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 2
Establishing correspondences between the query image and a database
of geo-referenced images [Cummins08, Chen11, Hansen01] Query
image
Slide 3
Standard Image-based Indoor Localization (2/3) Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 3 Querying
Quantization + td-idf weighting SIFT descriptors Image Database +
Inverted file Building a detailed database of environments is
troublesome Number of Images StorageTime
Slide 4
Problem Statement Miguel Loureno Institute for Systems and
Robotics, Faculty of Science and Technology, University of Coimbra
- 16 May 2012 - Slide 4 A complete coverage of the environment can
be performed with an para-catadioptric camera Distortion increases
the appearance difference between the images Our Contribution: A
new model-based SIFT method for matching between hybrid imaging
systems Query image
Slide 5
Presentation Outline Matching in Hybrid Imaging Systems
Comparison / drawbacks of the standard approaches Improvements to
the SIFT detector and descriptor Image-based IL using Hybrid
Imaging Systems Comparison of several database description schemes
Comparison of two searching approaches : BoV vs GVP Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 5
Slide 6
Matching in Hybrid Imaging Systems Miguel Loureno Institute for
Systems and Robotics, Faculty of Science and Technology, University
of Coimbra - 16 May 2012 - Slide 6 Using SIFT [Lowe04] on both
para- catadioptric and perspective images provides poor matching
results [Puig08] 10% inliers A straightforward solution is to apply
SIFT in a virtual camera perspective (VCP) [Schnbein11] Cylinder
Polar Standard approaches either render a Polar [ Puig08 ] or a
Cylindrical panorama [ Krishnan08 ]
Slide 7
Implicit cylindrical rectification - cylSIFT Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 7 Based on
our previous work [Lourenco12] we propose to perform the
cylindrical rectification implicitly inside SIFT framework -
cylSIFT How does SIFT work ? Image salient points detected in a
scale space framework SIFT descriptor is computed based on local
image gradient Render synthetic views require to reconstruct the
image signal Interpolation artifacts severely affect SIFT
performance [ Lourenco12 ]
Slide 8
Implicit cylindrical rectification cylSIFT detector Render the
cylinder before applying SIFT adds extra computational time and
interpolation artifacts Miguel Loureno Institute for Systems and
Robotics, Faculty of Science and Technology, University of Coimbra
- 16 May 2012 - Slide 8 Rectification > 2sec (Matlab ) We avoid
the reconstruction artifacts by using an adaptive Gaussian filter
[Lourenco12] *
Slide 9
Standard vs Adaptive Gaussian smoothing Inherent properties of
the standard Gaussian filter Space invariant filtering Decouple
convolution in X and Y directions Miguel Loureno Institute for
Systems and Robotics, Faculty of Science and Technology, University
of Coimbra - 16 May 2012 - Slide 9 Advantages of the Simplified
Adaptive Filter Isotropic filter that can be decoupled for each
image radius A filter bank can be computed offline and loaded into
memory Simplification of the adaptive filter
Slide 10
Implicit cylindrical rectification cylSIFT description Miguel
Loureno Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 10
Non-linear distortion modifies the local structures in the image
and, by consequence, the gradients are affected Changes in local
gradients of the image deteriorates SIFT descriptor performance
Proposed Solution: Compute gradients in the omnidirectional image
and implicitly correct them using the Jacobian matrix of the
cylindrical mapping function
Slide 11
Detection and Matching evaluation cylSIFT completely avoids
interpolation of the image signal Better repeatability and matching
with less computational burden Miguel Loureno Institute for Systems
and Robotics, Faculty of Science and Technology, University of
Coimbra - 16 May 2012 - Slide 11 cylSIFT has similar performance to
the VCP approach The VCP requires a priori knowledge of the view to
render to minimize viewpoints changes between the query and VCP
image Set ASet B Set C Set D
Slide 12
Standard Image-based Indoor Localization (3/3) How can a robot
use a standard camera for performing indoor localization? Compare
of two image searching schemes Standard Bags of Visual Words (BoV)
Geometry preserving Visual Phrases (GVP) [Zhang11] Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 12 Query
image
Slide 13
BoV: Standard Bags of Visual Words (BoV) Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 13 Length:
Dictionary Size Images are represented as the histogram of words
Drawback: Discard the spatial relation between words Spatial layout
can be relevant for disambiguate situations of perceptual
aliasing
Slide 14
GVP: Encoding weak geometric constraints [Zhang11] Miguel
Loureno Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 14 A B A B
Offset space A B Group of Visual Words in a certain layout form a
Visual Phrase GVP incorporate geometric constraints at the
searching step -3 -2 0 1 2 3 4 -1 0 1234 5 I I
Slide 15
Indoor Location Recognition - Experimental Setup Our database
covers 2 teaching buildings of our campus 118 para-catadioptric
images 451 perspective images are used to query the database The
environment suffers from high perceptual aliasing Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 15 ? Query
image
Slide 16
Retrieval Results Miguel Loureno Institute for Systems and
Robotics, Faculty of Science and Technology, University of Coimbra
- 16 May 2012 - Slide 16 cylSIFT takes full advantage of its
matching capabilities Interpolation avoidance assure more
distinctive descriptors 10% improvement of the localization success
when compared with a state-of-the-art approach (Cylinder + GVP)
[Chen11] Indoor recognition systems benefit with the usage of GVP
Robustness against perceptual aliasing (spatial layout matters) BoV
TOP 1GVP TOP 1 Re-ranking - Top 5
Slide 17
Take home messages Interpolation artifacts affect image
retrieval cylSIFT offers better retrieval performance in hybrid
imaging systems at a marginal computational cost when compared to
the standard SIFT algorithm cylSIFT can be useful for other
applications than localization Hybrid fundamental matrix estimation
[Puig08] First work that uses a hybrid imaging systems for image
retrieval without the need of rectification Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 17
Slide 18
Thanks for coming Questions? Code and dataset releases:
http://arthronav.isr.uc.pt/~mlourenco/OmniSearch/ Miguel Loureno
Institute for Systems and Robotics, Faculty of Science and
Technology, University of Coimbra - 16 May 2012 - Slide 18