1219 
The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
accuracy. The results of bundle block adjustment are assumed 
to be true position values. It provides initial attitude and 
heading without any alignments. IMU/GPS are initialized for 
the Kalman filter using the result of bundle block adjustment in 
ever 10 seconds. Namely, after every computation of bundle 
block adjustment, GPS/IMU and its error are corrected. Figure 
10 is the strapdown navigation algorithm for integrating 
GPS/IMU with the result of bundle block adjustment. The 
combination of GPS/IMU and bundle block adjustment can be 
called “hybrid IMU”. 
Figure 10. Strapdown navigation algorithm 
As the result of GPS/IMU which is corrected with bundle block 
adjustment, trajectory of hybrid IMU can assure sufficient geo- 
referencing accuracy for the CCD images. The trajectory of 
digital camera can be representative of the trajectory of the 
platform because GPS/IMU is initialized by camera orientation. 
This is one of the advantages of this system. GPS/IMU 
coordinate is fitted to digital camera coordinate. Figure 11 
shows the trajectory of the UAV in this experiment. Hybrid 
IMU is computed by aiding GPS/IMU and bundle block 
adjustment. The square dots are the timing of bundle block 
adjustment, GPS/IMU by the kalman filter is initialized by 
these points. The circle dots are the trajectory of GPS. The line 
is the Hybrid IMU, which is combined GPS/IMU and results of 
bundle block adjustment. 
Hybrid trajectory • GPS * CCD Images 
35.8985 35.8986 35.8987 35.8988 35.8989 35.899 35.8991 35.8992 35.8993 35.8994 
Latitude 
Figure 11. Trajectory of the UAV 
4. DIGITAL 3D MODEL 
time. For direct geo-referencing of laser range data and CCD 
images, hybrid IMU which are integrated by GPS/IMU and 
bundle block adjustment is used. There are only two coordinate 
systems, laser scanner coordinate system and the common 
world coordinate system, are existing. GPS/IMU and bundle 
block adjustment of CCD images already have the common 
world coordinate system. That is, just laser scanner coordinate 
system must be converted to the common world coordinate 
system by geo-referencing. Geo-referencing of range data is 
determined by the 3D helmert’s transformation which is 
computing rotation matrix and shift vector with hybrid IMU 
data and calibration parameters as offset. Offset from laser 
scanner to digital camera in body frame is already obtained by 
sensor calibration. 
All the points scanned by the laser scanner (x) are converted to 
the common world coordinate system (Xw) which is the same 
as digital camera coordinate system as given in equation (1). 
Rotation matrix (Rh) and shift vector (Sh) from hybrid IMU 
which corrects drift error are used with respect to time. Offset 
values (Rl-d and Sl-d) are already estimated in sensor 
calibration. 
Xw = (Rh * Rl-d) x + (Sh+ Sl-d) ( 1 ) 
Where Rh, Sh : hybrid IMU, Rotation and Shift 
Rl-d, Sl-d : offset by calibration 
Geo-referencing of laser range data and CCD images is done 
directly. Figure 12 shows the 3D point cloud data which is 
directly geo-referenced by hybrid IMU data. In this research, 
the world coordinate system of CCD images is used as the base 
coordinate system, so all points have the world coordinate 
system. 
Figure 12. 3D point cloud data 
4.2 Color rendering 
The digital surface model, which is a 3D model of the object 
surface, is manipulated using a computer. It is comprised of 3D 
measurements that are laid out on colored points cloud. These 
measurements use the 3D point cloud data, which are derived 
from laser scanner, and texture data, which is derived from 
CCD sensors. 
4.1 Direct geo-referencing 
While the measuring, the platform including all sensors is 
continuously changing its positions and attitudes with respect to 
The point cloud data acquired by laser scanner is geo- 
referenced by hybrid IMU data. This hybrid IMU data is based 
on the common world coordinate system, which is the same as