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Tree species discrimination by aid ofTemplate Matching Applied to Digital Air Photos
Jonas Bohlin, Håkan Olsson, Kenneth Olofsson and Jörgen Wallerman
Remote Sensing LaboratorySwedish University of Agricultural Sciences
Umeå
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Swedish National Land SurveyZ/I DMC camera
2003: test flights
2004: camera acquisition
2005: large areas photographed,radiometry issues
2006: first year new policy
2007: only digital production line
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Swedish National Land SurveyNew policy for air photgraphy
adopted 2005
1/3 of Sweden to be photographed yearly from 2006, No commercial tasks Normally: 4800 mSpecial areas: 3000 m
From 2007, only digital photos and only digital production
No similar policy yet for other sensors (e.g. satellite data, laser data)
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Thus, there will be large amounts of aerial photos available yearly which are:- digitally recorded - of high radiometric quality, - multispectral (blue – NIR), - affordable
Specific question in this study:can we separate spruce / pine / deciduous ?
Motivation:Swedish forests are dominated by 3 species: - 43% spruce - 40% pine - 12% birch (+ 5 % other deciduous)
Encouraging first results from Oct 2003
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Common approaches to single tree detection:
• Local maxima (e.g. Pinz, 1989) 2D
• Segmentation (e.g.Gougeon) 2D
• Template matching (R. Pollock, 1996) 2.5D
• DSM 3D
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The template matching idea
1. Several synthetic 3D model trees are generated,
2. The templates are rendered with appropriate 2D projection and illumination for each position in the image
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for different crown shapes:
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3. The templates are cross corellated with the image
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4. Local maxima in corellation images are selected
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5. Example of pattern of found trees
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Typical results from template matching in coniferous forest1
• Found trees 67 %• Missed trees 33 %• False positives: 10 %
More difficult in deciduous forests
1) Erikson, M & Olofsson, K. 2005. Comparision of three individual tree crown detection methods. Machine Vision and Applications. Vol. 16, no 4, 258-265.
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Two tests of tree species discrimination, using pan sharpened Z/I DMC, green, red, NIR bands
Test A Test B
Date 13 Oct 2003 28 June 2005
Flying altitude 3000 m 4800 m
No of trees 256 170
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Subset of Z/I DMC image, from 4800 m altitude, with one of five plots
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Plot with true tree positions and manually digitized visible canopies for validation
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Green = sunlit part of template hits
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Pixel values where selected for the templates (green) that had asufficient intersection with the manually identified crowns (red)
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Red
Gree
n
2001751501251007550
200
175
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125
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75
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Z/I DMC October 13, 2003
89 % correct classified
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Red
Gree
n
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200
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125
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75
50
Z/I DMC June 28, 2005
88 % correct classified using lda applied to green, red, NIR
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Z/I DMC October 13, 2003 in G, R, NIR colour space
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Conclusions• Considerable potential for tree species discrimination using
CIR digital air photos
• The relative spectral development among tree species over the season needs to be a re-discovered research topic
• Radiometry is still an issue after 2 season of DMC operations at the Swedish National Land Survey, larger studies are motivated when this is solved
How do we more easily capture a large material with trees with known species and connect it to the Z/I DMC images?
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5 cm pixel images can be used for validation of tree species
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UAV with digital camera developed by Steve Joyce, SLU, Umeå
Thank you for your attention