ONE-STEP AND TWO-STEP CALIBRATION OF A PORTABLE PANORAMIC IMAGE MAPPING SYSTEM

Transcription

1 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia ONE-STEP AND TWO-STEP CALIBATION OF A POTABLE PANOAIC IAGE APPING SYSTE Ping-Chuan Wang a, Po-Ching Tsai a, Yung-Chuan Chen b, Yi-Hsing Tseng a, * a Dept. of Geomatis, National Cheng Kung Univesity, #1 Univesity oad, Tainan, Taiwan ( peteson9623, fed , y1130)@gmail.om, tseng@mail.nku.edu.tw b Dept. of Constution Sene and Engineeing, De-Lin Institute of Tehnology, #1 Ln. 380, Qingyun d., Tuheng Dist., New Taipei City, Taiwan - y1130@yahoo.om Commission I, WG I/3 KEY WODS: Photogammety, Close ange, apping System, Platfoms, Calibation, Exteio Oientation. ABSTACT: A Potable Panoami Image apping System (PPIS) is poposed fo apid aquisition of thee-dimensional spatial infomation. By onsideing the onveniene of use, ost, weight of equipment, pesion, and powe supply, the designed PPIS is equipped with 6 ulaly aanged ameas to aptue panoamimages and a eeive fo positioning. The motivation fo this design is to develop a hand-held obile apping System (S) fo some diffiult aessing aeas by vehile S, suh as ugged teains, foest aeas, heavily damaged disaste aeas, and owed plaes et. This PPIS is in fat a assisted lose-ange photogammeti system. Compaed with the taditional lose-ange photogammety, PPIS an edue the need of gound ontol points signifiantly. Unde the ondition of knowing the elative geometi elationships of the equipped sensos, the elements of exteio oientation of eah aptued image an be solved. Howeve, the poedue of a system alibation should be done auately to detemine the elative geometi elationships of multi-ameas and the antenna ente, befoe the PPIS an be applied fo geo-efeened mapping. In this pape, both of one-step and two-step alibation poedues fo PPIS ae pefomed to detemine the leve-am offsets and boesight angles among ameas and. The pefomane of the one-step and two-step alibation is evaluated though the analysis of the expeimental esults. The ompaison between these two alibation poedues was also onduted. The two-step alibation method outpefoms the one-step alibation method in tems of alibation auay and opeation onveniene. We expet that the poposed two-step alibation poedue an also be applied to othe platfom-based Ss. 1. INTODUCTION With the development of geomatis, spatial infomation aessing is beoming faste and moe auate and pese. ost of the uent mobile mapping systems (Ss) integate multi-senso systems fo the aquisition of images, loations, oientation paametes, et. The INS/ integated systems ae useful beause of its apid diet geo-efeenng apability (Shin, 2005). ost Ss use a vehile as a platfom (El- Sheimy, 1996), whih is onvenient fo the data olletion of oad eahable aeas. Howeve, many mapping aeas ae not allowed a vehile to ente, suh as ugged teains, foest aeas, heavily damaged disaste aeas, owed plaes et. Ellum (2001) developed a Bakpak obile apping System (BS), whih integates a amea, a eeive, an inlinomete, and a ompass. By onsideing the ost, weight of equipment, pesion, and powe supply, we popose an altenative vesion of BS, whih is alled a Potable Panoami Image apping System (PPIS). The PPIS is a potable platfom mounting six light ameas (fo aptuing panoamimages) and a eeive. The eeive an povide instant positioning fo eah pitue taking position. Ou pototype of PPIS is less than 3 kg, whih an be hand-held to ollet the spatial infomation fo some aeas that a vehile-based S annot ente. It is espeally useful fo emegeny mapping of some disaste aeas. Befoe the PPIS an be applied fo geo-efeened mapping, the elative geometi elationships among the ameas and the antenna should be alibated. This poedue is ommonly alled system alibation, whih is usually pefomed in an outdoo field to detemine the leve-am offsets and boesight angles (Ellum, 2001; Habib et al., 2011). The omputation of system alibation is based on the bundle-adjustment theoy, and the quality of alibation is highly dependent on the distibution of the ontol points in the alibation field. In ode to obtain the exteio oientation of eah image, evey image should ove enough numbe of well distibuted ontol points. It is eally diffiult to find a qualified outdoo alibation field. Although ou outdoo alibation field ontains moe than 200 ontol points distibuted on the walls of 4 suounding buildings, it baely fulfils the alibation equiement. Howeve, it is elatively easy to set up an indoo alibation field with a good distibution of ontol points. Theefoe, instead of applying this one-step alibation method, this pape poposes a two-step alibation method. The fist stage of the two-step method is to detemine the elative geometi elationship of the ameas using an indoo panoami alibation field. Then, the seond step is to detemine the leve-am offset between the amea set and the antenna ente using a simple outdoo alibation field ontaining only a few ontol points. * Coesponding autho. 173

2 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia 2. THE DESIGN OF PPIS The PPIS is in fat a assisted lose-ange photogammeti system, whih is omposed of thee pats: the platfom, the amea set and a eeive. Fig. 1(a) shows a pitue of the whole system and Fig. 1(b) shows that the system is set up on a suveying od. The total weight of the platfom, ameas and the antenna is less than 3 kg, so that it an be aied by a peson fo data olletion. ou pototype of PPIS, we hose the Sony Nex-3 amea (Fig. 3), whih is a single-lens digital amea weights less than 300 gams. The amea uses a COS senso. The senso size is 23.4 x 15.6 mm, and the image esolution is 4592 x 3056 pixels. The hoizontal field of view (FOV) of the amea is about 65 and the vetial FOV is about 43. Eah of the six ameas will always be installed in the same position on the platfom. The six ameas ae numbeed fom 0 to 5. The amea numbeed 0 is the blak one indiated with a yellow le in Fig. 2(a). The oientation of this amea will also be used as the oientation of the platfom. Figue 3. The adopted digital ameas (Sony Nex-3) fo ou pototype of PPIS. 2.3 eeive (a) Figue 1. (a) A pitue of the PPIS; (b) The system is set up on a suveying od. 2.1 Platfom The platfom is designed to mount six ameas fo simultaneously aptuing six images to ompose a panoama image. The platfom, theefoe, has a hexagon shape as shown in Fig. 2(a). The dimension of the platfom is 40m x 40m x 35m. When the platfom is installed on a suveying od, the total height is about 2.4 m. On the platfom, thee ae six holes and loks to fix the six ameas. The pole in the middle of the platfom has a standad sew to fix a antenna. The six ameas an be tiggeed simultaneously with a mehanial devie, whih is omposed of six sting-ontolled leves. The amea tigge mehanism an be opeated with a sting-pulling ing attahed on the suveying od as shown in Fig. 2(b). (b) The PPIS employs a eeive to detemine the position of pitue taking in high auay. Fast positioning is also equied fo the use of PPIS in an unstable envionment. Unde this umstane, the eal-time kinemati (TK) positioning method is adopted. Fotunately, the National Land Suveying and apping Cente (NLSC) in Taiwan has set up a netwok TK system based on Vitual efeene Station (VS) tehnology, whih is alled e- (Eletoni Global Positioning System). This system allows a use to pefom TK with a VS eeive though a netwok ommuniation with a mobile phone to the e- ontol ente. This e- system an detemine a position instantly in the auay about 3~5 m. A Timble VS eeive is adopted fo ou pototype of PPIS as shown in Fig. 1(a). In ase the e- is not available, one an one neaby base station to pefom apid elative positioning though a post poessing of baseline omputation. It means that e- is used fo onveniene but not fo equiement. If the antenna and eeive ae attahed togethe, they should be mounted togethe on the platfom and inease the weight of the hand-held unit. Some eeives ae onneted with thei ontol units and ae sepaated fom the antennas. By using this kind of eeives, only the antenna needs to be mounted on the platfom and the othe pats an be aied with a bag o a bakpak. Fig. 4 shows the use of this kind of eeive. (a) Figue 2. (a) The top view of the platfom; (b) The bottom view of the platfom. (b) 2.2 Cameas The PPIS platfom mounts six ulaly aanged ameas to aptue panoamimages. The adopted ameas should be light weight and should stable in taking high quality images. Among the ommeal amea bands nowadays, we found that light-weight single-lens ameas ae most qualified ameas. Fo Figue 4. The use of antenna sepaated eeive fo the platfom. 174

3 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia 3. SYSTE CALIBATION Befoe the PPIS an be applied fo geo-efeened mapping, the alibation of amea inteio oientation and a system alibation to detemine the geometi elationship of the sensos must be pefomed. The alibation of amea inteio oientation an be pefomed using egula lose-ange photogammeti softwae. This pape mainly deals with the method of pefoming the system alibation. The theoy of system alibation involves the definition of applied oodinate systems. The PPIS involved oodinate fames ae the body fame, the amea fames and the mapping fame. If an S is integated with /INS, the body fame usually efes to the INS oodinate fame. Due to absene of the INS on PPIS, the oientation of a efeenng amea is adopted. The body fame of PPIS is illustated in Fig. 5. The body fame is defined by the phase ente of antenna as the oigin, and the axes of the body fame is defined paallel to the photo oodinate axes of the efeenng amea whih is the blak one numbeed 0. The body fame of PPIS is atually defined by antenna position. It is, theefoe, also alled the fame in this pape. The ommon definition of the amea fame applied in photogammeti theoy is adopted. Fig. 5 also shows the axes of the amea fames of PPIS. The mapping fame is any loal objet oodinate system, whih may be deived fom some neaby ontol points. Figue 5. The body fame and the amea fames of PPIS. The elationship of the antenna ente, the amea pespetive ente, and an objet point is shown in Fig. 6. The oodinates of an objet point an be alulated though Equation 1 (Ellum, 2001). The otation matix of the i th amea an be detemined by Equation 2. The leve-am offsets and boesight angles should be alibated pesely. whee P P (1) p : objet oodinates of point P in the mapping fame :the position of the in the mapping fame :The position of the in the amea fame :Camea oodinates of point P in the amea p fame :The otation matix fom the amea fame to the mapping fame whee (2) :The otation matix fom the i th amea fame to the fame (body fame) :The otation matix fom the fame (body fame) to the mapping fame Figue 6. elationship of antenna ente, amea pespetive ente, and an objet point (Ellum, 2001). Fo the expeiments onduted in this study, an outdoo alibation field ontains moe than 200 ontol points distibuted on the walls of 4 suounding buildings was established fo one-step alibation. An indoo alibation field with hundeds of photogammety tagets was also set up fo two-step alibation. 3.1 One-step Calibation The one-step alibation is pefomed using the outdoo alibation field. The PPIS took images on 4 stations in the alibation field. All ontol points on the images and manually seleted onjugate image points wee measued aefully. The omputation of one-step alibation is based on the bundleadjustment theoy. All exteio paametes inluding the pespetive entes ( ) and oientation matixes ( ) of the i th amea be detemined though a bundle-adjustment pogam. Afte the omputation, the boesight angle an be alulated though Equation 3, whih is deived fom Equation 2. The antenna position in the mapping fame,, an be alulated using Equation 4. The leve-am, i, theefoe an be alulated though Equation 5. 1 ( ) (3) (4) ( 1 ) ( ) (5) Based on the bundle-adjustment theoy, the quality of alibation is highly dependent on the numbe and distibution of tie and ontol points in the alibation field. In ode to obtain the exteio oientation of eah image, evey image should ove enough numbes of well distibuted ontol points. It is eally diffiult to find a qualified outdoo alibation field. Although ou outdoo alibation field ontains moe than two hunded ontol points distibuting on the walls of 4 175

4 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia suounding buildings, it baely fulfils the alibation equiement. 3.2 Two-step Calibation It is elatively easy to set up an indoo alibation field with a good distibution of ontol points. Theefoe, this pape poposes a two-step alibation method. The fist stage of the two-step method is to detemine the elative geometi elationship of the ameas using an indoo panoami alibation field. Then, the seond step is to detemine the leveam offset between the amea set and the antenna ente using a simple outdoo alibation field ontaining only a few ontol points. In the fist stage of two-step alibation, the PPIS without the eeive takes images on 4 stations in the indoo alibation field. Taget odes ae used in the indoo alibation field, whih an be measued automatially by using a photogammeti pogam (Fase, 1997; Cok and Fase, 2008). All exteio paametes inluding the pespetive entes ( ) and oientation matixes ( ) of the i th amea an be detemined though a bundle-adjustment pogam. Afte the omputation, the boesight angle an be obtained fom 0 whih is alulated though Equation 6, and i an be alulated though Equation 8, whih is deived fom Equation ( i ) 0 (6) whee 0 :The otation matix fom the i th amea 0 fame to the efeenng amea whih is the blak one numbeed 0 i 0 i 0 1 ( ) ( 0 i 0 (7) ) (8) The indoo alibation field is shown in Fig. 7. Hundeds of photogammety tagets ae well distibuted along the walls, eiling, and floo. Afte aptuing images at seveal stations, the inteio oientation paametes (IOPs) and exteio oientation paametes (EOPs) an be alulated automatially by bundleadjustment softwae. The elative geometi elationships among ameas an be detemined using the amea EOPs. Duing the fist stage of the two-step alibation method, the leve-am offsets and boesight angles among ameas an be detemined pesely using the amea EOP esults of indoo alibation. Figue 7. Indoo alibation field The outdoo alibation field is shown in Fig. 8. Thee ae 6 gound stations whih oodinates wee detemined by using. About 200 ontol points on the walls of fou suounding buildings wee hosen. The oodinates of ontol points wee detemined by taditional suveying. Afte aptuing images at seveal gound stations, hundeds of tie points wee measued manually, and the EOPs of images ould be alulated automatially by using bundle-adjustment softwae. Leve am offsets among antenna ente and ameas an be detemined using the oodinates of stations and the EOPs of ameas. The one-step alibation method needs a lot of ontol points, but the two-step alibation just needs fewe ontol points beause the elative geometi elationships of ameas has been alibated pesely within the indoo alibation stage. In ode to alibate the leve-am offsets i, the seond stage of the two-step alibation method should be pefomed as onestep alibation method using the outdoo alibation field. The boesight angle an be detemined in the fist stage of the two-step alibation method, it is not neessay to alulate the boesight angle in the seond stage of the two-step alibation method. So ompaed with the one-step alibation method, it is an be expeted that the pesion of the boesight angle using the two-step alibation method will be impoved. 4.1 Test Fields 4. EXPEIENTS Two test fields ae designed to alibate the leve-am offsets and boesight angles among ameas and : an indoo alibation field and an outdoo alibation field. 4.2 esults and Analysis Figue 8. Outdoo alibation field One-step alibation was pefomed in an outdoo alibation field, but two-step was pefomed both in an indoo alibation field and an outdoo alibation field. Afte one-step o two-step alibation, the leve-am offsets and boesight angles among ameas an be detemined. In ode to ompae one-step and two-step alibation esults, elative distane fom the pespetive ente of the efeenng amea (amea 0 ) to the othe ameas wee alulated (Fig. 9). An aveaging poess was pefomed to obtain mean values of elative distanes, and thei standad deviations wee shown in table 1. Compaed with 176

5 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia the one-step alibation method, the esults of the two-step alibation poedue an lagely impove the pesion of the leve-am offset among ameas. Figue 10. elative distane fom the antenna ente to pespetive entes of ameas Figue 9. elative distane fom the pespetive ente of the efeene amea (amea 0 ) to the othe ameas Table 1. Standad deviations of elative distane fom pespetive ente of efeenng amea (amea 0 ) to the othe ameas (unit: m) Cameas ethod One-step Two step Eo anges of oientation angles of six ameas wee shown in table 2. The eo anges of boesight angles wee used to alulate the positioning pesion in the 20 metes. Compaed with one-step alibation method, the two-step alibation poedue an impove the pesion of the boesight angles among ameas. Table 2. Eo anges of boesight angles of six ameas and position pesion in 20m ethod ω φ κ One-step Two step 0.02~ ~ ~ ~2.9m 1.3~3.0m 0.6~2.7m 0.01~ ~ ~ ~0.7m 0.2~0.6m 0.5~0.9m Afte one-step o two-step alibation, the leve-am offsets among the antenna ente and ameas an be detemined. In ode to ompae one-step and two-step alibation esults, elative distane fom the antenna ente to the pespetive entes of the ameas wee alulated (Fig. 10). Afte aveaging, standad deviations of elative distane fom the antenna ente to the pespetive entes of ameas wee shown in table 3. Compaed with the one-step alibation method, the two-step poedue didn t impove the pesion of leve-am offsets among the antenna ente and ameas. Table 3. Standad deviations of elative distane fom antenna ente to pespetive entes of ameas (unit: m) ethod dx dy dz One-step Two step The expeimental esults demonstate that the two-step alibation poedue is supeio to the one-step alibation poedue in tems of alibation auay among ameas. But the two-step alibation method still an t impove the pesion of leve-am offsets among and ameas. Fo example, the two-step alibation poedue an impove the pesion of leve-am offset and boesight angle among the efeenng amea (amea 0 ) and amea 1, but it still an t impove the pesion of leve-am offset among the antenna and amea 1 5. CONCLUSIONS A PPIS and its system alibation poedue ae implemented and tested in this pape. Compaed with a vehile-based S, PPIS povides the benefits of potability, simplified opeation, oveoming the mapping limitations in elief teain, and edution of equipment ost. This system is expeted to be onveniently applied to spatial infomation olletion fo disaste aeas. The system alibation of PPIS an be done though the onestep o two-step alibation methods. The leve-am offsets and boesight angles of PPIS an be alulated afte the alibation poedue. The two-step alibation method outpefoms the one-step alibation method in tems of alibation auay and opeation onveniene. The expeimental esults show that the two-step alibation poedue lagely impoves the pesion of boesight angles among the ameas although the pesion of leve-am offsets is not impoved muh. Also, the onveniene and stability of the two-step alibation method ae supeio to the one-step alibation method. We expet that the poposed two-step alibation poedue an also be applied to othe platfombased Ss if thei multi-ameas,, and INS ae igidly mounted on a steady platfom. 177

6 Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Senes, Volume XXXIX-B1, 2012 XXII ISPS Congess, 25 August 01 Septembe 2012, elboune, Austalia EFEENCES Conk, S. and Fash, C. S., Hybid easuement Senaios in Automated Close-ange Photogammety. The Intenational Ahives of the Photogammety, emote Sensing and Spatial Infomation Sene. Vol. XXXVII. Pat B3b, pp , Beijing. Ellum, C., The Development of a Bakpak obile apping System. UCGE epots No Depatment of Geomatis Engineeing, Univesity of Calgay. El-Sheimy, N., The Development of VISAT - A obile Suvey System fo GIS Appliations. UCGE epots No Depatment of Geomatis Engineeing, Univesity of Calgay. Fase, C. S., Digital Camea Self-alibation, ISPS Jounal of Photogammety and emote Sensing, Vol.52, pp Habib, A., Kesting, A. P., Bang, K., au, J.,2011. A Novel Single-step Poedue fo the Calibation of the ounting Paametes of a multi-amea Teestial obile apping System. In Poeeding of the 7th Intenational Symposium on obile apping Tehnology, Poland. Shin, E. H., Estimation Tehniques fo Low-Cost Inetial Navigation. PhD Thesis, Depatment of Geomatis Engineeing, Univesity of Calgay, Calgay, Canada. ACKNOWLEDGENT This eseah wok was sponsoed unde the pojet gants: NSC E-224-Y2 and NSC E-219-Y2. The authos appeate fo the suppot of the National Sene Counl, Taiwan. 178