Three-Dimensional Measurement of a Remote Object with a Single CCD camera

Transcription

1 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, Three-Diensional Measureent of a Reote Object with a ingle CCD caera CEG-CU CE *, CE-CIE U, TI-O WG #, CU-WEI UG * Departent of Electrical Engineering, t. John s University 499 Ta ing Rd., ec. 4, Ta-ui, Taipei County, 535 TIW chaung@ail.sju.edu.tw Departent of Electrical Engineering, Takang University 5 Ying-chuan Rd., Ta-ui, Taipei County, 537 TIW # Departent of Electronic Engineering, t. John s University 499 Ta ing Rd., ec. 4, Ta-ui, Taipei County, 535 TIW bstract: - This paper presents a novel ethod by regulating the height of a CCD caera to easure the width and height of a targeted object. That is, three-diensional easureent can be obtained with the use of a single CCD caera. To facilitate the easureent using various kinds of CCD caeras, paraeters pertinent to the caeras can be established via a proposed echanis in this paper. s a result, any kinds of CCD caeras can be used to perfor three diensional easureent of a targeted object via software ipleentation of the proposed easuring ethod. o changes to the circuits or structure of the caera are required. eywords: - CCD caera, distance easureent, three-diensional easureent. Introduction There are generally two ways for easuring distance: contact and non-contact approaches. For non-contact easureent, various solutions can be used, like ultrasonic distance easureent []-[], laser reflection ethods [3]-[4]. ecause these two ethods use the theory of reflection, object reflectivity plays an iport role. If the reflection surface is undesired, the easuring syste generally perfors poorly or not at all. On the other hand, iage-based easuring systes based on pattern recognition or iage analysis techniques [5]-[6] generally deand huge aount of storage capacity and high-speed DP processors, which inevitably iposes a critical constraint for practical applications. To overcoe the probles and difficulties encountered by the existing techniques, an iage-based easuring syste without coplex calculation entitled Iage-ased Distance Measuring yste (IDM) is presented in this paper. The configuration of the proposed IDM [7]-[9] is very siple, consisting of only a single CCD caera and two parallel laser projectors beside the caera. ecause the disposition of the laser projectors and the optical origin of the CCD caera, which for a straight line, two laser-projected spots will appear on the sae scan line in a CCD iage. s a result, processing a single scan line, rather than the whole iage, is only required to identify the projected spots in the CCD iage. The ethods of coputing coplex video signals of a whole iage via either pattern recognition or iage analysis are therefore no longer required. ased on an established relationship between the distance and pixel counts between the projected spots on a CCD iage, 3-diensional easureent of a distant object can be obtained via this proposed ethod. ote that the ethod proposed in this paper is quite different fro those which use two CCD caeras [0]-[] during the easuring. y regulating the height of a CCD caera, only one CCD caera is only required to overcoe the proble of iage loss []-[3]. ecause the sae paraeters are used for taking pictures through out the easureents before and after the regulation of the CCD caera, thus we are able to increase the accuracy of the easureent. The iage of the targeted object in iages changes, when the CCD caera goes straight up or down. Therefore, by using a vertical scan line, we are able to know the iage oveent without the need to process the whole iage. nowing the variation of pixel counts in the iages because of the

2 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, caera oveent, we can obtain three-diensional easureent of the targeted object by using the proposed ethod. Practical experients will be conducted in this paper to validate the effectiveness and viability of the proposed approach. The paper is organized as follows. ection introduces the distance easuring ethod. The proposed three-diensional easureent is described in ection 3. The deterination of intrinsic paraeters for digital caeras is given in ection 4. Experient results are presented in ection 5. Conclusions are drawn in ection 6. control rod Optics rule Δh W W θ θ Δh Z Z Y OC a Y OC b The Distance Measuring yste Fig. shows the diagra of the easuring syste, where a shaft is used to control the height of the CCD caera along the vertical direction. The distance due to up and down of the caera can observed by the optical ruler. particular distance of the oveent can also be obtained via settings of switches W and W. When the CCD caera oves along the vertical direction, the object in iages will according ove vertically as shown in Fig., siilar to the distance easuring systes [0]-[] using the two CCD caeras. In this paper, a single CCD caera is only used, which circuvents the probles of easuring inaccuracy due to different caera paraeters during the easureent. The convenience of the proposed approach where oveent of the caera is directed along the vertical direction also contributes to the easureent accuracy. Other siilar easuring systes include the triangular easuring ethod [7] and parallel easuring ethod [8]-[9]. These two ethods, however, have to use two laser projectors for projecting laser beas onto the targeted object siilar to an optical ruler, based on which easureent of distance can proceed. This fixture of the CCD caera together with the laser projectors is not easy to install. The projection of laser beas also requires extra electricity supply. Fig. Diagra of the easuring syste. C Fig. Moveent of the objects in iages due to the oveent of the CCD caera. When the CCD caera is vertically oved for Δ h, objects in the iage will ove as well in ters of pixel variation. s shown in Fig., the oveent of the object in the iage is easured and represented as Δ pixels. In what follows, we will describe the relationship between Δ h and Δ in detail. Δ C (0) s C (0) θ the angle of view θ s the angle of view Fig. 3 Distance easureent via the proposed approach.

3 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, Fig. 3 illustrates the iage fro the horizontal (view ) and vertical (view ) view angles respectively for a single iage. ote that a single CCD caera, rather than two CCD caeras, is used at the sae. The oveent of the CCD caera is Δ h, resulting a pixel variation of Δ in the iage. To better explain the proposed approach, the observation of iage in Fig. 3 fro the vertical angle is re-drawn as Fig. 4, where the relationship between the pixel variation Δ, caera oveent Δ h, view angle θ v, and distance fro the targeted object can be better perceived. 3 Three-Diensional Measureent via the proposed approach While the photographing distance is, the height of triangle ( P O, P, PR ) will be. The distance between P and P is the axial real-world R distance covered by the vertical view angle θ. Previous research [7]-[9] has already shown that the scan tie between two points in the iage is proportional to their corresponding distance. s far as CCD caera is concerned, pixel counts and distance between P and P are in direct proportion. ased on R the relationship aong the pixel variation Δ and caera oveent Δ h, can be expressed as follows: Δh = (), where is the axial pixels in a vertical scan line of an iage frae. y a triangular relationship, when the included angle and the base line are known, the height ( ) can be obtained s:, where optic origin, and = cotθ () is the distance between CCD caera and θ is vertical view angle of the CCD v θ are the intrinsic paraeters of caera. and easureent. ow and θ can be accurately derived for various kinds of CCD caeras will be fully elaborated in next section so as to achieve a better easuring accuracy. s shown in Fig 4, and are height of the targeted object under easureent, thus =, =. The forula for the height of the targeted object can be expressed as: = = Δh = Δh (3) o atter the observations are ade either fro the horizontal or vertical view angle, the photographing distance between the CCD caera and the targeted object reains the sae, i.e. =. The forula of the axial real-world distance when viewing fro the horizontal direction can be expressed as: = ( + ) tanθ (4) ssue that the distance between two points C and C on the targeted object is C. ased on the pixel nubers between points C and C, obtained via the forula below: can be C C C = (5), where is the axial pixel nubers in the horizontal scan line of the CCD caera and θ is horizontal view angle. s results, () stands for the photographing distance between the CCD caera and the targeted object (Z direction). (3) and (5) represent the height (Y direction) and width ( direction) of the targeted object, respectively. y doing so, three diensional easureent of a distant object can be obtained by using only a single CCD caera via the proposed easuring ethod. P Opticalaxis θ P O Fig. 4 Illustration of easureent fro the view angle. PR

4 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, Deterination of the intrinsic paraeters for CCD caeras set of intrinsic paraeters of the CCD caera are required for using the proposed distance easuring syste, including, θ, θ. To iprove easuring accuracy, a proposed easuring schee is proposed in this section for identifying these paraeters. θ θ θ P P R R P orizontal ruler CCD caera P O h s ertical Fig.5 Mechanis for obtaining intrinsic paraeters for a CCD caera s shown in Fig. 5, when the horizontal scan line of the CCD caera is parallel to the horizontal ruler, we have θ = θ, = and, =, indicating the easuring paraeters are established fro the horizontal view angle. Turning the CCD caera 90 degrees, the easuring paraeters are then established fro the vertical view angle, i.e. θ = θ, =, =. When the horizontal ruler is positioned at and R, the height will be and distance between points P and P R on the iage is. When the horizontal ruler is positioned at and R, the height will be and distance between points P to P R on the iage will be. s a result of the triangle theore by observing triangles Δ ( PO, P, P ) and Δ P, P, P ), we have the following relationship: ( O ruler P R R =, where = or ( ) cotθ =, where = or (6) (7) In an attept to validate the perforance of the proposed approach, a Panasonic DMC- CCD caera is used in this paper for all the experients conducted. The easuring paraeters associated with the CCD caera include = 0. 4 c, cot θ =.8, and cot θ =.. The horizontal and vertical resolution in ters of pixels of the CCD caera are = 364 and = 448, respectively. When these easuring paraeters are available, the height and the width of the targeted object in addition to the photographing distance can be obtained via the proposed ethod. Without aking changes to the structure of the CCD caera, the proposed easuring syste can easily achieve the objective of three-diensional easureent of a targeted object by oving the caera straight up or down. 5 Experient results s shown in Fig., the proposed easuring syste oves the CCD caera with a specific distance in the vertical direction for obtaining the easureent of a targeted object. Measureent results and photos during the experients are presented below. Fig.6 Photos before and after caera oveent at photographing distance = 40 c

5 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, Fig. 7 Photos showing different photographing distances with Δ h =0c s deonstrated in the experient results, the easureent accuracy via the proposed syste has been significantly iproved in coparison to the IDM (Iage-ased Distance Measuring yste) [7]-[9]. 6 Conclusion In this paper, we have proposed a easuring syste based on the oveent of a CCD caera along the vertical direction. either extra distance-easuring sensors nor physical easuring rulers are required to achieve a satisfactory easureent via the proposed ethod. s long as the caera oveent becoes available, we can deterine the pixel counts for a targeted object due to the caera oveent to calculate the photographing distance as well as the height and width of the object. ecause of the proposed ethod to accurately deterine the intrinsic paraeters for various CCD caeras, any caera can therefore be adopted to obtain satisfactory results of three-diensional easureent via the proposed ethod. s deonstrated in the experient results, distance inforation can be easily incorporated into the photos taken. On the basis of the existing research results, the next objective of the research tea is to investigate as to how autoatic distance easureent can be achieved based on only one vertical scan line. Reference: [] lessio Carullo, Franco Ferraris, and alvatore Graziani, Ultrasonic Distance ensor Iproveent Using a Two-evel eural etwork, IEEE Transactions on Instruentation and Measureent, ol. 45, o., pp , pril 996. [].Caarullo and M. Parvis, n ultrasonic sensor for distance easureent in autootive applications, IEEE ensors Journal, ol., o., pp.43-47, 00. [3]. Osugi,. Miyauchi,. Furui, and. Miyakoshi, Developent of the scanning laser radar for CC syste, JE Rev. 0, pp , 999. [4].-T. shin, ehicles Crashproof aser Radar, M.. thesis, Opt. ci. Center, ational Central Unive., Chung i City, Taiwan, R.O.C., 000. [5] anade, T., ano,., iura., Developent of a ideo-rate tereo Machine, Proc 995 IEEE/RJ Int. Conf. on Intelligent Robots and ystes, Pittsburgh, U, ugust, 995, ol. 3, pp.95-00(995). [6] Tanaka, Y, gofuku,., agai, I., Mohaed,.:Developent of a Copact ideo-rate Range finder and its application, Proc. 3rd Int. Conf. on dvanced Mechatronics, Okayaa, Japan, ugust, 998, pp [7] Ming-Chih u, Wei-Yen Wang, and ung-sun ian, Iage-ased hight easuring syste for liquid or particles in tanks, IEEE International Conference on etworking, ensing and Control, ol., pp.4-9, 004. [8] Ming-Chih u, Wei-Yen Wang, and Chun-Yen chu, Optical-ased Distance Measuring yste (ODM), The Eighth International Conference On utoation Technology, pp.8-85, 005. [9] Ming-Chih u, Wei-Yen Wang, and Chun-Yen Chu, Iage-ased Distance and rea Measuring yste, IEEE ensors Journal. ol. 6, o., pp , pril 006. [0] M.. id-hed and M. T. oraie, Dual caera calibration for 3-D achine vision etrology, IEEE Trans. Instru. Meas., vol. 39, no. 3, pp.5-56, Jun [] C. iguori,. Pietrosanto, and. Paolillo, n on-line stereo vision syste for diensional easureents on rubber extrusions, in Proc. th IMEO TC4 Int. y., isbon, Portugal, ep 3/4, 00, pp.5-9. [] J. Weng,P. Cohen, and M. erniou, Caera calibration with distortion odels and accuracy evaluation, IEEE Trans. Pattern nal. Mach. Intell., vol. 4, no. 0, pp , Oct.99. [3] M. Rebiai,. Mansouri, F. Pinson, and.. Tichit, Iage distortion for zoo lenses: Modeling and digital correction, in Proc. Int. road-casting Convention, 99, pp

6 Proceedings of the 7th WE Int. Conf. on ignal Processing, Coputational Geoetry & rtificial ision, thens, Greece, ugust 4-6, () Measureent of photographing distances: Table Results of distance easureent at Δ h =0c distance ( ) Measured distance ( ) Error % 0.307% 0.3% 0.35% 0.40% 0.333% () Measureent of height and width: Table Results of height easureent at Δ h =0c distance ( ) height( ) Measured height ( ) Error % 0.83% 0.88% 0.54% -0.6% % Table 3 Results of width easureent at Δ h =0c distance ( ) height( ) Measured height ( ) Error 0.9% 0.585% 0.567% 0.43% 0.506% 0.359%