Webcams in context

Abrams, Austin; Pless, Robert

doi:10.1145/1873951.1873997

Cited by 12 publications

References 15 publications

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Heliometric Stereo: Shape from Sun Position

Abrams

Hawley

Pless

2012

Computer Vision – ECCV 2012

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Abstract. In this work, we present a method to uncover shape from webcams "in the wild." We present a variant of photometric stereo which uses the sun as a distant light source, so that lighting direction can be computed from known GPS and timestamps. We propose an iterative, non-linear optimization process that optimizes the error in reproducing all images from an extended time-lapse with an image formation model that accounts for ambient lighting, shadows, changing light color, dense surface normal maps, radiometric calibration, and exposure. Unlike many approaches to uncalibrated outdoor image analysis, this procedure is automatic, and we report quantitative results by comparing extracted surface normals to Google Earth 3D models. We evaluate this procedure on data from a varied set of scenes and emphasize the advantages of including imagery from many months.

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Heliometric Stereo: Shape from Sun Position

Abrams

Hawley

Pless

2012

Computer Vision – ECCV 2012

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Finding Jane Doe: a forensic application of 2D image calibration

Stylianou¹,

Abrams²,

Pless³

2013

5th International Conference on Imaging for Crime Detection and Prevention (ICDP 2013)

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Thirty years ago, a young girl was found decapitated. Her identity remains unknown, and neither her head nor her killer have been found. Until recently, the location of her grave was lost, preventing any efforts to identify her using modern forensic techniques. This paper presents a case study on the use of burial photos to accurately and precisely determine the location of the lost grave. We highlight challenges in finding good correspondences between points in thirty year old imagery and the actual scene today, characterize the sensitivity of a camera calibration's geometric constraints to inaccuracies in these correspondences, and discuss an interactive tool that allows an analyst to quickly identify problems with them. Using the geolocation pipeline and tools discussed in this paper, we localized the lost grave to an approximately 1.6 meter long uncertainty region. On June 16, 2013, the Saint Louis Police Department performed an exhumation according to this localization, quickly finding the body.

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