We describe the participation of the CERTH/CEA LIST team in the Placing Task of MediaEval 2015. We submitted five runs in total to the Locale-based placing sub-task, providing the estimated locations for the test set released by the organisers. Out of five runs, two are based solely on textual information, using feature selection and weighting methods over an existing language model-based approach. One is based on visual content, using geo-spatial clustering over the most visually similar images, and two runs are based on hybrid approaches, using both visual and textual cues from the images. The best results (median error 22km, 27.5% at 1km) were obtained when both visual and textual features are combined, using external data for training.
http://ceur-ws.org/Vol-1436/
http://www.multimediaeval.org
Including Mental Health Support in Project Delivery, 14 May.pdf
MediaEval 2015 - CERTH/CEA LIST at MediaEval Placing Task 2015
1. CERTH/CEA LIST at MediaEval Placing Task 2015
Giorgos Kordopatis-Zilos1, Adrian Popescu2, Symeon Papadopoulos1 and
Yiannis Kompatsiaris1
1 Information Technologies Institute (ITI), CERTH, Greece
2 CEA LIST, 91190 Gif-sur-Yvette, France
MediaEval 2015 Workshop, Sept. 14-15, 2015, Wurzen, Germany
2. Summary
#2
Tag-based location estimation (2 runs)
• Based on a geographic Language Model
• Built upon the scheme of our 2014 participation [2] (Kordopatis-Zilos et
al., MediaEval 2014)
• Extensions from [3]: improved feature selection and weighting
(Kordopatis-Zilos et al., PAISI 2015)
Visual-based location estimation (1 run)
• Geospatial clustering scheme of the most visually similar images
Hybrid location estimation (2 run)
• Combination of the textual and visual approaches
Training sets
• Training set released by the organisers (≈4.7M geotagged items)
• YFCC dataset, excl. images from users in test set (≈40M geotagged items)
8. Locality – value distribution
#8
london (6975), paris (5452), nyc (3917)
luminancehdr (0.0035), dsc6362 (0.003), air photo (0.002)
9. Extensions
• Spatial Entropy (SE) function
– calculate entropy values applying the Shannon entropy formula in the tag-cell
probabilities
– build a Gaussian weight function based on the values of the tag SE
#9
• Internal Grid
– Built an additional LM using a finer grid, cell side length of 0.001°
– combine the MLC of the individual language models
15. References
#15
[1] Y. Jia, E. Shelhamer, J. Donahue, S. Karayev, J. Long, R. Girshick, S. Guadarrama,
and T. Darrell. Caffe: Convolutional architecture for fast feature embedding.
arXiv preprint arXiv:1408.5093, 2014.
[2] G. Kordopatis-Zilos, G. Orfanidis, S. Papadopoulos, and Y. Kompatsiaris.
Socialsensor at mediaeval placing task 2014. In MediaEval 2014 Placing Task,
2014.
[3] G. Kordopatis-Zilos, S. Papadopoulos, and Y. Kompatsiaris. Geotagging social
media content with a refined language modelling approach. In Intelligence and
Security Informatics, pages 21–40, 2015.
[4] A. Popescu. CEA LIST's participation at mediaeval 2013 placing task. In
MediaEval 2013 Placing Task, 2013.
[5] K. Simonyan and A. Zisserman. Very deep convolutional networks for large-
scale image recognition. In International Conference on Learning
Representations, 2015.
[6] O. Van Laere, S. Schockaert, and B. Dhoedt. Finding locations of Flickr resources
using language models and similarity search. ICMR ’11, pages 48:1–48:8, New
York, NY, USA, 2011. ACM.