International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
In Haala (2003) terrestrial laser scanning was combined with 
panoramic images and surface of tree trunks were extracted to 
analyse tree species. Digital camera has been used to measure 
individual tree variables from the digital images in the field 
(Juujárvi et al. 1998). Lee et al. (2003) presented automated 
methods of tree boundary extraction and Clark et al. (2000) 
digital terrestrial photogrammetric methods for tree stem 
analysis. 
The objective of this paper was to develop a photogrammetric 
method based on terrestrial digital images in order to measure 
the geometric shape and derive parameters of individual trees. 
The method does not require special instruments, time 
consuming tacheometer measurement or positioning of image 
capture location. Equipments required are a digital camera, 
camera platform, hypsometer, compass, reference scale bar and 
measurement tape. Error sources of suggested method are 
analysed separately. This digital-image-based method will be 
used to verify previously developed geometric 3D tree model 
(Pyysalo & Hyyppà 2002). 
2. MATERIALS 
2.1 Test area, field measurements and laser acquisitions 
The test area locates in urban environment in the city of Espoo, 
Finland. Area is park type university campus with lots of 
vegetation. 30 trees (pines, spruces and birches) were chosen as 
test trees. 16 trees were imaged from one direction only and 14 
trees from two directions. Trees were chosen from group of 50 
trees. Tacheometer measurements have been carried out to 
locate tree trunk positions and digital elevation model profiles. 
Area has been scanned with airborne laser twice. The first one 
was measured from aeroplane with German Toposys instrument 
in late spring 2000. Flying height was 400 m, scanning 
frequency 80 0000 Hz and cone diameter of laser footprint 20 
cm in ground. Swedish Topeye instrument measured same area 
in late summer 2002 from helicopter flying in 200 meters. Pulse 
cone diameter in the ground was 20 cm. 
2.2 Instrument 
Images were taken using Nikon E-10 digital camera. Camera 
was mounted to camera platform with flexible elevation and 
rotation possibilities. Maximum image size, 3008x2000, pixels 
was utilized and fixed size of camera aperture. During the 
measurement camera was manually focused to the eternity, 
which is also the same position the camera was calibrated. 
3. METHOD 
3.1 Terrestrial imaging 
Several tests were carried out in the field to find optimal image 
capture workflow. The crown dimension measurement task 
required that both the base and tree crown top would be visible 
in the same image. In the same time image should be captured 
as close as possible for detailed measurement and also because 
during the tests it was observed that even in sparse forests other 
trees or other objects were typically shadowing the target tree if 
the image shooting distance was too long. The camera stand 
was approximately 1.5 meters high and imaged trees were 20-35 
meters in height. 
The applied image capture workflow was as follows: 
e The image capturing location was chosen from 20-30 
meter distance from the tree. 
e Camera stand was levelled according to bubble level. 
* The optical axis of camera was levelled horizontally 
(® = 0). 
e Angle K was set to zero using tube level. 
e Reference scale bar was attached to the tree trunk. 
e Camera was rotated around y-axis (¢) in the position 
where trunk was in the middle of the image. 
e  (Q was set to 20° angle was measured using 
hypsometer. 
e After capturing the image angle ¢ was measured with 
compass. 
e Distance to the tree was measured. 
  
Figure 1. Image capture. Camera was rotated in the position 
where trunk was in the middle of the image (up left). Reference 
scale bar was attached to tree trunk (up right). Camera was 
rotated 20? (bottom left). Distance to the tree was measured 
(bottom right.) 
After imaging a tree the same process was repeated from 
another location for the same tree so that image capture 
directions were perpendicularly towards each other. 
3.2 The image pre-processing 
In the image pre-processing distortion errors were removed 
utilizing camera calibration file (Figure 3). The calibration was 
carried out for shortest focal length f, which was utilized in 
image capturing. The images where rectified to plane parallel to 
the trunk (Figure 2). 
  
   
    
   
   
    
   
  
    
  
      
  
    
    
   
   
   
   
  
    
  
  
  
  
  
  
   
  
   
   
  
   
    
    
   
    
     
    
   
  
  
  
   
   
    
  
  
  
   
  
  
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