2. AUTOMATIC EXTERIOR ORIENTATION USING
VIDEO IMAGE AND STILL IMAGES
This section describe about the automatic exterior orientation
process in this investigation.
In order to perform automatic detection of corresponding points
from discontinuous high resolution still images without using
coded target or manual operation, the keypoint detector and
descriptor such as SIFT (D. G. Lowe. 2004.) or SURF (H. Bay.
2006.) are widely used now. By the way, if assume that the
video image between discontinuous still images are obtained,
video image sequences gives information about the motion of
corresponding points. Therefore, the authors developed the
procedure of automatic detection of corresponding points using
video image sequences and high resolution still image.
Moreover, robust exterior orientation that using corresponding
points, GPS on UAV and minimum ground control point was
also investigated.
2.1 Integrated Devices on UAV
The authors have developed the UAV system which has ability
of acquiring video image and still image simultaneously.
Figurel shows the UAV system of this investigation. This
system is based on “AscTec Falcon8” which developed by
"Ascending Technologies GmbH". Tablel shows the details of
integrated devices of this UAV system. The finder image of
digital still camera RICHO GX200 is connected to video
recorder by NTSC video line. Therefore, high resolution still
images (12 mega-pixels) at each waypoint and the video image
(VGA size) during a flight are obtained. The synchronization
between video image and still images is performed by detection
of shuttered frame from video image sequences. Also, the
positioning results at each waypoint are obtained by KML
format file as the function of “AscTec Falcon 8”.
Figure 1. UAV of This Investigation
UAV ASCTEC Falcon 8 Payload: 500g
Flight Time: 16-18 min
GPS Ublox LEA-5T GPS L1 frequency, C/A Code
GALILEO Open Service L1 frequency
SBAS surport
Resolution:4000x3000 Pixel
Focal Length: £-5.1 mm(at wide side)
Input Video Signal: NTSC/PAL
Recording Resolution: 640 x 480 pixel
Video File Format: AVI (mepg4)
Tablel. Details of Integrated Devices
Digital Camera Ricoh GX-200
Video Recorder] kingdom System
Technology
Angel Eye
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
2.2 Flow of Automatic Exterior Orientation procedure
Figure 2 shows the flow of automatic exterior orientation
procedure in this investigation. The waypoint planning and
flight control are performed by “AscTec autopilot control
software” provided by Ascending Technologies GmbH. High
resolution still images at waypoints, video image during flight,
and also positioning information of each waypoint are obtained
as the result of a flight. At the first of this processing, the
detection of common feature points from high resolution still
image and tracking of detected feature points on video image
sequences are performed using robust feature point tracking
method based on the OC image processing. The tracking result
of feature points are obtained in the image coordinate on high
resolution still image. As the next step, sub-pixel matching of
each feature point is performed. The good results of this sub-
pixel matching are used as candidate of correct pass points. In
order to perform tie point matching, the exterior orientation
using these candidate pass points is performed. The result of
exterior orientation in this step gives the geometry of candidate
pass points and still images in arbitrarily position and scale.
Finally, registration in global coordinate using the positioning
information of waypoints and minimum ground control points is
performed by using bundle adjustment with robust regression.
These photogrammetric procedures are developed based on
“TOPCON Image Master”. Therefore, the 3D modelling from
still image also can be performed easily.
Waypoint Planning and Flight
(ASCTEC Falcon 8)
}
Robust Feature Point Tracking
(OC image processing)
!
Sub-pixel Matching
(LSM)
i
Tie Point Matching
and Exterior Orientation
(in arbitrarily position and scale )
| Bundle Adjustment with Robust Regression|
3D Modeling
on “Topcon Image Master?’
Figure 2. Flow of Automatic Exterior Orientation
2.3 OC Image Processing
In this investigation, the detection of common feature point and
tracking procedure are performed by “Orientation Code” (OC)
image processing. The most unique point of OC image
processing is that the coded images are used instead of the
original gray-scale images. The OC means a quantization of the
maximal intensity change direction around interest pixel. The
OC of each pixel is defined as following equation:
