Automatic acquisition of 3D spatial data in city with air-borne TLS Three Line Scanner
Yoshiaki Kagawa and Ryosuke Shibasaki
Center for Spatial Information Science and
Institute of Industrial Science,
University of Tokyo
4-6-1 Komaba, Meguro-ku, Tokyo 153-8505
Tel: 81 -3-5452-6417 Fax 81 -3-5452-6417
E-mail: kagawa@skl.iis.u-tokyo.ac.jp
JAPAN
Key Words
TLS Three Line Scanner , three-dimensional spatial data, laser scanner , stereo matching,
Abstract
Recently, automatic generation of three-dimensional data in city from aerial images are needed for three-dimensional GIS and revision of GIS database. Though digital or analogue aerial photograph or sequential CCD image data are conventionally used for this purpose, the accuracy and reliability is not sufficient especially for urban area where height of terrain and building surfaces have abrupt changes. Instead, the authors are developing an integrating sensors consisting of three line scanner TLS and laser scanner. TLS is made of three CCD line sensor located in parallel on the imaging plane and has capability of triplet observation, which will have higher accuracy and capability in three-dimensional data generation. By integrating with a laser scanner, reliability of high-resolution three-dimensional city data generation will be improved. In this study, we describe the system configuration and methodology of making three-dimensional data from TLS and the laser scanner using an experimental flight data.
1. Introduction
Recently, three-dimensional data in city are needed, because as compared with two-dimensional data, three-dimensional data can describe detail of city, which enables us conduct more accurate and detailed simulation or analysis on urban areas. Examples of the simulations or analysis are wind simulation around high-rise buildings, fire propagation simulation, flooding analysis and propagation/reflection analysis of electric waves for telecommunication.
Mainly, there are two methods for generation of three-dimensional data. First method is using optical sensor like CCD camera. This method is a successor to traditional analogue aerial photo. But resolution of two dimensional CCD camera is not very sufficient for generating accurate 3D city data generation. Second method is using laser scanner. Laser scanner is an equipment that radiates laser beam to objects and measure distance form the scanner to the object using the return time of the radiated laser beam. When the position of scanner and angle of radiation of laser are known, three-dimensional coordinates of object can be calculated directly. By swinging the laser beam, many data points are obtained, but the resolution is lower than that of CCD sensor. Although studies on application of the individual technologies are conducted, but the possibilities of the combination of both technologies have never been explored using real data. So, in our study, objective is to develop methodology of making three-dimensional data from optical sensor and the laser scanner using an experimental flight data. And as optical sensor, new hardware -Three Line Scanner was used.
2.Three Line Scanner TLS
Three Line Scanner TLS is an optical sensor for aerial survey. Three Line Scanner has three linear CCD located in parallel to get image of three directions -forward, nadir, and backward, which is oriented perpendicular to the flight direction of aircraft. Image is generated due to the aircraft motion by scanning the terrain surface. Fig1
Fig1 : method of getting data with TLS
Differently from CCD frame sensor (two dimensional CCD), the exterior orientation must be computed for each scan-line. The specification of the Three Line Scanner used in this study is shown in Table1. Using linear CCD, the resolution of the image is very high. Single line has 10200 pixels. Ground resolution of the image reaches 5 cm when the flight height is 500m. Flight path and high frequent vibration have a blurring effect on the image, which necessitates the development of stabilizer to absorb the vibration.
Table1 : system specification of TLS
| CCD
|
Number of Pixel/Line
|
10200 Pixels
|
| Pitch of Pixel
|
7 um
|
| Number of CCD
|
|
3 (Monochrome), 1 (RGB)
|
| Number of Shades
|
|
(4096 Shades) 12 Bit
|
| Lens
|
Distance of Focus
|
60mm
|
| Angle of stereo
|
|
21 °
|
| Number of Line
|
|
500 Line/Second
|
