THE EFFECTS OF REFLECTING SURFACE MATERIAL PROPERTIES ON TIME-OF-FLIGHT LASER SCANNER MEASUREMENTS

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1 ISPRS SIPT IGU UCI CIG ACSG Tabl of contnts Tabl ds matièrs Authors indx Indx ds auturs Sarch Rchrchs xit Sortir TH FFCTS OF RFLCTING SURFAC MATRIAL PROPRTIS ON TIM-OF-FLIGHT LASR SCANNR MASURMNTS D D Lichti Dpartmnt of Spatial Scincs Curtin Univrsity of Tchnology GPO Box U1987 Prth, WA 6845 AUSTRALIA B R Harvy School of Survying and Spatial Information Systms Th Univrsity of Nw South Wals Sydny, NSW 252 AUSTRALIA Abstract Trrstrial lasr scannrs, such as th Cyrax 25 and its prdcssor th 24, us pulsd lasr ranging and rotating mirrors to accuratly masur dns sts of thr-dimnsional co-ordinats of ntir surfacs. Rang is obsrvd by masuring th two-way tim of flight (TOF) of th rflctd lasr puls. Th rflctorlss natur of th rangfindr raiss th possibility of rang rrors du to puls attnuation by th rflcting surfac. This papr rports on an invstigation into th ffcts of rflcting surfac proprtis on TOF lasr scannr masurmnts mad with a Cyrax 24. Tsts wr conductd at clos rang (3m) and mdium rang (53m). Svral sampls of construction matrials and rocks from Wstrn Australia having various surfac roughnss and minral composition wr tstd with both dry and wt rflcting surfacs. Rsults prsntd show no significant rang rrors du to diffring matrial proprtis, but do xhibit changs in rang masurmnt distribution and rturn signal intnsity. Ky words: lasr scanning, surfac rflctanc, tim-of-flight ranging. 1. Introduction Ground-basd lasr scanning is an mrging tchnology that is attracting a grat dal of intrst within svral aras of gomatics. Th high tmporal scanning frquncy, high spatial point dnsity, accuracy and rflctorlss natur of scanning systms ar som of th salint proprtis attracting th attntion. Documntd applications includ dformation monitoring (Lichti t al., 2), structural assssmnt of a bridg (Gordon t al., 21), landslid monitoring (Kurisak t al., 21), ic cav mapping (Ullrich t al., 21), mapping th intrior of buildings (Runn t al., 21) and building façad masurmnt (Balzani t al., 21; Ullrich t al., 21). A tim-of-flight (TOF) systm masurs rang, ρ, by obsrving th two-way travl tim, t, of a short (5-5ns in duration; Amann t al., 21) puls of lasr light, 1 ρ = c t (1) 2 whr c is th vlocity of light. Th rflctorlss natur of th rangfindr mans thr is no nd to plac rtro-rflctiv targts on th objct to b masurd. Rang to th surfac is masurd providd that a sufficint amount of puls nrgy is rflctd so as to rgistr a signal with th scannr s photodtctor. Th currnt gnratd by th dtctor must xcd a prdfind thrshold in ordr for th rturn tim to b obsrvd. In considring rflctorlss TOF masurmnt systms, a qustion that naturally ariss is: What is th influnc of th rflcting surfac matrial proprtis? Two aspcts of this qustion must b considrd. Th first is th ffct on th maximum rang that can b masurd. Nglcting atmosphric ffcts, rflction-rlatd nrgy losss may b attributd to diffus scattring, absorption and transmission if th matrial is translucnt. Ullrich t al. (21) provid a plot of maximum rang as a function of rflctivity for th RIGL scannr (λ=9nm). As might b xpctd, th curv shows that maximum rang to matrials with low rflctivity (.g., coal) is considrably low in rlation to highly rflctiv matrials such as whit masonry. Th scond aspct is th rang dlay rror, δρ, corrsponding to a timing rror, δt, causd by th attnuatd amplitud of th rflctd lasr puls. Godin t al. (21) dmonstrat a small (4µm) rang bias du to subsurfac scattring in translucnt marbl for an activ lasr triangulation systm (i.., not a TOF systm). Gordon t al. (21) rport on rrors in Symposium on Gospatial Thory, Procssing and Applications, Symposium sur la théori, ls traitmnts t ls applications ds donnés Géospatials, Ottawa 22

2 Cyrax 24 rang masurmnts from rtro-rflctiv targts thought to b du to photodtctor saturation. It is acknowldgd that any ffct from non-rtro targts is unlikly to b of consqunc for applications such as as-built survys and stockpil volum masurmnt. Howvr, as lasr-scanning tchnology bcoms mor widly availabl and accptd, it is incrasingly likly to b applid to projcts dmanding gratr accuracy for which such rang rrors may b of significanc. This papr rports th findings of an invstigation into th ffcts of rflcting surfac proprtis on TOF lasr scannr masurmnts. Numrous rock and construction matrial sampls with diffrnt surfac roughnss, minral composition and colour wr tstd. Tsts wr prformd on ach spcimn with both dry and wt rflcting surfacs. A varity of survying rflctors was also scannd. Tsting was conductd at clos and mdium rang. Following a rviw of rflction of lctromagntic radiation (MR), th xprimnt dtails ar dscribd. Quantitativ assssmnt of th ffcts on rflcting surfac on both rang and rturn signal intnsity ar thn prsntd, followd by conclusions. 2. Rflction of lctromagntic Radiation Th rflctanc of a particular sampl is govrnd by incidnc angl, surfac roughnss and th matrial proprtis, which includ lctric prmittivity, magntic prmability and conductivity (Jlalian, 1992). Various masurs xist to quantify rflctanc, such as spcular, hmisphrical and bi-dirctional (Wolf, 1998). Hr, masurs basd upon matrial proprtis of th rflcting surfac ar rviwd. Considring th cas of spcular rflction from a smooth surfac at normal incidnc, th cofficint of rflction, r, is givn by (Fowls, 1975) r 1 N r = = (2) i 1+ N and th rflctanc, R, is givn by whr i is th amplitud of th incidnt lctric fild; r is th amplitud of th rflctd lctric fild; * indicats complx conjugation; and N is th complx indx of rfraction, givn by whr n κ is th rfractiv indx of th matrial; is th xtinction indx; and * ( 1 N)( 1 N) ( 1 + N)( 1 + N) * R = (3) N = n + jκ (4) j = 1. Sinc th currnt producd by an optical dtctor in rspons to an incidnt lctromagntic fild is proportional to th squar of th amplitud (i.., th powr; Wolf, 1998), q. 3 is th most rlvant masur of rflctanc for th prsnt discussion. Th rfractiv indx, dfind as th ratio of th vlocity of light in a vacuum to that in a givn mdium, is a function of th lctric prmittivity and magntic prmability (Fowls, 1975), n = KK m (5) whr K is th rlativ lctric prmittivity; and K m is th rlativ magntic prmability. Th xtinction indx dtrmins how much MR is absorbd by th mdium, and is givn by (Fowls, 1975) c κ = α ω (6) whr α is th cofficint of absorption; and ω is th frquncy of th MR.

3 For a dilctric (insulator) matrial, th xtinction indx approachs zro so th rfractiv indx is ral and th rflctanc bcoms 2 ( 1 n) ( 1+ n) 2 R = (7) For conducting mdia (.g., mtals), th xtinction indx is larg and both it and th rfractiv indx also dpnd upon lctric conductivity, σ. For a non-magntic mdium, th rlativ prmability is unity, so th rfractiv indx is solly a function of th lctric prmittivity. Th spcimns tstd in this study fall undr th catgory of non-magntic dilctrics. 3. xprimnt Dscription To quantify th ffcts--if any--of rflcting surfac matrial proprtis on pulsd lasr rang masurmnts, an xprimnt was conductd using th Univrsity of Nw South Wals School of Survying and Spatial Information Systms Cyrax 24 (prdcssor to th 25) lasr scannr. Th Cyrax 24 offrs ±4mm rang-accuracy, ±6µrad (12 ) angular accuracy and maximum rang of about m. Co-ordinat accuracy is quotd as ±6mm up to a rang of 5m. Rotating mirrors dflct th grn lasr (λ=532nm) puls to provid masurmnt of thr-dimnsional co-ordinats rfrncd to th scannr s intrnal co-ordinat systm. In addition to th co-ordinats, th Cyrax also provids a unitlss, normalisd masur of rturn signal nrgy loosly trmd intnsity that rangs btwn and 1. Svral diffrnt hand-sizd rock spcimns and construction matrials (brick, concrt and limston block) collctd from around Wstrn Australia wr scannd. Tabl 1 provids a summary of ach spcimn, including colour, composition, approximat planar surfac ara scannd and a qualitativ dscription of th planar surfac roughnss. Th chosn sampls providd a varity of colours and minral compositions for th study. Som wr takn from North Dandalup dam southast of Prth, th subjct of a prvious scanning campaign with a nar infrard scannr (Lichti t al., 2). Othrs wr takn from th Curtin Univrsity campus, whr in anothr study (Gordon t al., 21), a scannr similar to th on dscribd abov was unabl to rgistr rturns from th construction matrials, in particular th rd brick. Thus, thr was much intrst in thir masurmnt in this study. Tabl 1. Summary of Spcimns. Spcimn Colour of Planar Surfac and Composition Planar Surfac Ara (cm 2 ) Planar Surfac Finish Rd Brick Homognous: brownish rd; opaqu 86 Smooth Limston Homognous: whit; opaqu 75 Smooth Whit Granit Htrognous: whit with black crystals; opaqu 28 Smooth Black Coal Homognous: black; opaqu 5 Smooth Concrt Homognous: gry; opaqu 6 Rough Limston Block Homognous: cram; opaqu 24 Rough Basalt Homognous: black; opaqu 13 Smooth Latrit Htrognous: orang with brown and black crystals 24 Smooth with a fw hols Whit Quartz Homognous: whit with linar black minral intrusions; translucnt 24 Smooth Th irrgularly shapd rock spcimns wr cut with a rock saw to giv a smooth, planar surfac to scan and hnc minimis scattring du to diffus rflction. Th concrt and limston block sampls had planar facs rsulting from thir manufactur, but wr somwhat roughr than th cut rock surfacs. Th cut fac of th latrit sampl possssd a fw hols du to its larg (.g., visibl) crystal structur. Th xpctd consqunc of ths txturs was incrasd diffus scattring. Svral typs of rtro-rflctiv survying targts wr also scannd, including a standard DM prism, cat y targts (both whit and rd) and traffic rflctors. Strong rturns wr xpctd du to thir rtro-rflctiv natur. Th gomtry of th xprimnt is illustratd in Figur 1. ach rock sampl was placd on a plan tabl at th sam hight as th scannr with its planar surfac vrtical and normal to th scannr s Z-axis to nsur normal incidnc of th lasr. Th planar surfac of ach rock was carfully alignd with th tabl dg and lvlld using a stsquar. ach rock was shimmd in plac for scanning with a tack adhsiv. Ths masurs wr takn with th viw to positioning ach sampl at th sam spatial distanc from th scannr. Th planar surfac of ach spcimn was locatd.612m in front of a wall.

4 Indpndnt masurmnts with a stl rulr wr takn to nsur that ach spcimn was accuratly orintd. Any obsrvd rang diffrncs btwn sampls could thn b attributd to matrial ffcts on th rflctd signal. Y Z X Spcimn with planar surfac alignd with tabl dg. Scannr Plan Tabl Figur 1. xprimnt Stup. Two scans of ach sampl wr capturd: on dry and on wt. A film of watr was applid to th rflctiv planar surfac with a squirt bottl without moving th spcimn to ascrtain th ffcts of surfac moistur on rang masurmnt. Th tim btwn watr application and scan compltion was on th ordr of a fw minuts. Th xprimnt was conductd at two rangs: 3m (clos rang) and 53m (mdium rang). Th lattr was chosn sinc th ±6mm Cyrax positioning accuracy is quotd for rangs up to 5m. Th clos rang xprimnt was conductd indoors, whilst th mdium rang tsting was prformd outdoors du to spac limitations. Tmpratur was masurd at th tim of ach scan, though th first vlocity corrction was insignificant in vry cas. ach surfac was scannd with a nominal sampling intrval of 2mm in both th x and y dimnsions. This providd svral hundrd masurmnts pr spcimn. In som cass, mor than on thousand sampls wr acquird. Th rsulting point clouds wr ditd so that only th rturns from th planar rflcting surfac wr rtaind for data analysis. Th sampls wr chosn for thir rang of colour and minral composition. Colour indicats th rgion of th visibl spctrum th spcimn rflcts most strongly. Givn th varity of colours on would xpct ach to xhibit diffrnt rflctanc (q. 3). It is worth noting that non of th spcimns wr grn, th colour of th Cyrax lasr. Most sampls had homognous minral composition, with th xcptions bing th whit granit and th quartz. Th formr had a black and whit spckld colour, though th crystals wr much smallr (i.., a fw millimtrs across) than th lasr spot ( 5-6mm). Th quartz was translucnt whit with a linar, black minral intrusion. Th translucnc gav ris to th possibility of intrnal scattring of th lasr (c.f. Godin t al., 21). 4. Rsults and Analysis 4.1 Rang and Intnsity at 3m Analysis of th 3m xprimnt findings rvald that diffrncs in man rang (-Z) wr prsnt btwn sampls, but wr at th lvl of individual point standard dviations, which rangd from ±4 to ±9mm. Though possibly du to matrial diffrncs, thy can most likly b attributd to alignmnt rrors in spcimn placmnt. Diffrncs btwn th wt and dry masurmnts, which wr not subjct to alignmnt rrors, wr on th ordr of 1-2mm (with basalt bing th xcption at 6mm), much lowr than th individual point standard dviations. No significant diffrncs xistd btwn th dry and wt standard dviations.

5 Thr rpat scans of th rd brick wr obtaind prior to th dry and wt surfac tsting. Th brick was not movd btwn scans in this cas. No diffrncs xistd in th first two momnts of th rang (-Z) and intnsity () data. Figur 2 shows th histogram of rang and intnsity masurmnts for th rd brick rpatability tst. In ach cas, th rang histogram has a ngativly skwd shap, indicating that shortr rangs wr mor probabl than longr rangs. ach histogram also xhibits a bimodal structur. A local maximum is visibl at approximatly Z=-3.7m, particularly in scans 1 and 3. Th bimodal apparanc suggsts that multipl rturns wr rcivd from th rd brick. Th physical rason for this bhaviour is not known, as th brick surfac was planar and rturns from surrounding objcts wr rmovd prior to analysis. Th intnsity histograms ach hav a unimodal, positivly skwd shap. 15 Scan 1 2 Scan 1 F rqu 5 F rqu Scan Scan 2 2 F rqu 5 F rqu Scan Scan 3 2 F rqu 5 F rqu Z (m) Figur 2. Rang (-Z) and Intnsity () Histograms from th Rd Brick Rpatability Tsts. Plottd in Figur 3 ar th dry and wt surfac rang histograms of thr diffrnt matrials. Though slightly diffrnt in apparanc, all xhibit a ngativly skwd shap. Th rd brick histogram is similar to thos in Figur 2, though th scondary pak is lss pronouncd. Th ffct of surfac moistur appars to b a slight transformation of histogram shap, which is most vidnt for th black coal spcimn. Howvr, it must b rcalld that thr was no significant chang to th first two statistical momnts of th rang for ths sampls. Sinc man intnsity was th most significantly affctd statistic, wt and dry rsults at both rangs ar prsntd in Tabl 2. Full rporting of th rsults can b found in Lichti and Harvy (22). Not surprisingly, th whit and cram colourd matrials xhibitd th gratst dry surfac rflctanc at 3m as indicatd by th intnsity attribut. For xampl, th man intnsity of th whit limston was.39. Also not surprising was th low rflctanc of th black coal, for which man intnsity was.17. Th addition of surfac moistur had mor of an ffct on som sampls than on othrs, with no colour or surfac finish dpndnc visibl. Howvr, du to variations in surfac finish among th spcimns, rflctanc diffrncs wr attributd to a combination of matrial proprtis and surfac roughnss. Intnsity standard dviation incrasd as a rsult of applying watr to th rflcting surfac (.g., whit granit: ±.5 dry, ±.16 wt), with th xcption of two cass (limston block and rd brick) whr no chang was obsrvd. Intrstingly, a dramatic incras in basalt man-intnsity was obsrvd (.3 dry,.59 wt). Many sampls with an intnsity of 1. wr rcordd, which indicatd dtctor saturation.

6 Figur 4 shows th intnsity histograms of th dry and wt surfacs for th sam spcimns from Figur 3. In ach cas, th dry histograms hav a positivly skwd shap. Th dry rd brick histogram-shap closly rsmbls thos of Figur 2. Th wt surfac histograms show much gratr disprsion. Svral local maxima at highr intnsity valus ar also visibl. Tabl 2. Man Intnsity Summary. Man Intnsity 3m 53m Spcimn Dry Wt Dry Wt Rd Brick Limston Whit Granit Black Coal Concrt Limston Block Basalt Latrit Whit Quartz Rd Brick (dry) 25 Rd Brick (wt) 2 2 F rqu 15 5 F rqu Limston (dry) Limston (wt) F rqu 15 5 F rqu Coal (dry) Coal (wt) F rqu 15 5 F rqu Z (m) Z (m) Figur 3. Rang (-Z) Histograms for Thr Matrials at 3m, Dry and Wt. 4.2 Rang and Intnsity at 53m Th magnituds of rang (-Z) point standard dviations at 53m wr commnsurat with thos at 3m. Som diffrncs xistd in rang on th ordr of point standard dviation magnitud. Ths rsults wr subjct to alignmnt rrors and lss wll-controlld atmosphric conditions (outdoors) ovr th 16m optical paths. Diffrncs in man rang of up to 3mm wr obsrvd btwn wt and dry sampls. As with th 3m tst, th whit and cram colourd matrials xhibitd th gratst dry rflctanc at 53m (.g., limston man intnsity was.28). Onc again, th black coal xhibitd th lowst man intnsity at.1. Intnsity valus at 53m wr gnrally lowr, likly du to gratr atmosphric attnuation ovr th longr path and, in gnral, wr about half th intnsity of th sam matrial at 3m. In contrast to th clos rang xprimnts, application of surfac moistur causd a

7 dcras in man intnsity, with fw xcptions. No incras in intnsity standard dviation was obsrvd du to surfac moistur, as was th cas at 3m. 5 Rd Brick (dry) 5 Rd Brick (wt) 4 4 F rqu 3 2 F rqu Limston (dry) Limston (wt) F rqu 3 2 F rqu Coal (dry) Coal (wt) F rqu 3 2 F rqu Figur 4. Intnsity () Histograms for Thr Matrials at 3m, Dry and Wt. 4.3 Scanning of Survy Targts No rsults hav bn prsntd for th scans of th survying rflctors. Du to thir rtro-rflctiv natur, most lasr rturns saturatd th Cyrax s photodtctor, which yildd intnsity attribut valus of 1.. Visual inspction of th point clouds rvald significant rang biass du to th saturation at both 3m and 53m. This would suggst that traditional survy targts ar not appropriat for us with lasr scannrs. 4.4 Imaging th Lasr Spot Picturd in Figur 5 is an imag of th Cyrax 24 lasr spot projctd onto a propritary Cyra targt. Th targt consists of an 8 x 8cm squar of grn film and a 3cm diamtr whit circl. Th imag was capturd with a digital camra during a high-dnsity scan of a small rgion of th targt. Th spot is slightly longatd in th vrtical dimnsion du to its upward scanning motion during imag xposur. Sinc th camra was opratd in automatd mod, th xposur sttings wr not availabl. Clarly, though, th shuttr spd was slowr than th Hz scan-rat. Th spot visibl in Figur 5 is likly th suprposition of svral spots. Th spot diamtr in th dirction orthogonal to th scan motion was masurd to b approximatly 5.5mm, which agrs with th Cyra spcification that it is lss than 6mm for th rang -5m. It is important to not that th distribution of irradianc within th lasr bam spot is not uniform but Gaussian, so no distinct point of rfrnc xists for a diamtr dfinition. Svral spot diamtr dfinitions xist, with th most common bing th 1/ 2 irradianc lvl diamtr (Matthws and Garcia, 1995). Th spatial fluctuations of spot intnsity ar du to spckl nois, a random intrfrnc pattrn inhrnt to lasr imaging systms causd by surfac roughnss on th scal of th lasr wavlngth. Th horizontal intnsity cross-sction xtractd from th digital imag brightnss valus, plottd in Figur 6 (th imag pixl spacing was 9µm), also shows th spckl nois. Not that th intnsity profil is clippd at 255 du to saturation of th camra s CCD dtctors. If not clippd, th

8 profil trnd would xhibit a Gaussian shap. Th profil floor (BV 5) rprsnts th rflction of ambint light by th grn targt film. Figur 5. Imag of Cyrax Lasr Spot on a Cyra Targt u a l V ss tn B righ Position (pixls) Figur 6. Lasr Spot Horizontal Cross-Sction. 5. Conclusions A st of xprimnts has bn conductd in an attmpt to quantify possibl rang rrors from a TOF scannr systm du to rflcting surfac matrial proprtis. Masurmnts wr succssfully obtaind from all matrials at all rangs; no

9 problms with lack of rturns wr ncountrd as in Gordon t al. (21). Though diffrncs btwn spcimns wr obsrvd, thy could not b attributd to matrial proprtis du to possibl alignmnt rrors. Rang diffrncs btwn wt and dry spcimn masurmnts that wr immun to alignmnt rrors wr obsrvd. Howvr, sinc thy wr at or blow th prcision of individual rang masurmnts, thy wr dmd insignificant. Th lack of rang rrors may b du to rturn puls amplitud adjustmnt prformd by th scannr lctronics. Intnsity attribut diffrncs wr obsrvd btwn spcimns and btwn dry and wt surfacs. At clos rang, intnsity incrasd in most cass whn th rflcting surfac was wt. At mdium rang, most sampls xhibitd a dcras in intnsity whn wt. Th practical consqunc of this outcom is possibl rduction in maximum scanning rang if th rflcting surfac is wt. An incras in intnsity attribut disprsion masurd was obsrvd for wt surfacs at 3m, but not at 53m. Th incras at 3m may b du to th watr film bing th dominant rflctor. That th ffct was not obsrvd at 53m may b du to a gratr vaporation rat outdoors. As wll as dry and wt ffcts, intnsity dcrass with an incras in distanc to th targt. In gnral, intnsity at 53m was found to b about half th intnsity of th sam matrial at 3m. Histogram analysis indicatd that th rangs ovr small, planar surfacs normal to th scannr axis followd a nonsymmtric distribution, for which nar rangs wr mor probabl than far rangs. Th analytical form of th probability dnsity function of th rang obsrvations is a function of rrors in th wav front (.g., spckl) and th mthod of dtction usd by th Cyrax systm, i.., incohrnt or cohrnt dtction (Andrws t al., 21). Th ffcts of surfac moistur wr found to b a slight shap altration to th histogram of rangs and significant altrations to th intnsity histogram. In anothr part of th xprimnts, th Cyrax lasr spot was imagd with a digital camra. Th captur of this imag givs ris to th possibility of thr-dimnsional spot positioning, say via digital photogrammtry or thodolit dirction masurmnts. This would b usful for indpndnt accuracy assssmnt and dvlopmnt of calibration procdurs and is th focus of ongoing rsarch. Rfrncs Amann, M-C, T Bosch, M Lscur, R Myllylä and M Rioux (21) Lasr ranging: a critical rviw of usual tchniqus for distanc masurmnt. Optical nginring. 4(1): Andrws, L C, R L Phillips and C Y Hopn (21). Lasr Bam Scintillation with Applications. SPI Prss: Bllingham, WA. Balzani, M, M Pllgrinlli, N Prftti, P Russo and F Ucclli (21) Trrstrial 3D lasr scannr: prliminary accuracy tsts. In Procdings of th Italy-Canada 21 Workshop on 3D Digital Imaging and Modling Applications in Hritag, Industry, Mdicin and Land. 8 pp. Fowls, G R (1975) Introduction to Modrn Optics. Scond dition. Dovr Publications Inc: Nw York, NY. Godin, G, M. Rioux, J-A Braldin, M Lvoy, L Cournoyr and F Blais (21) An assssmnt of lasr rang masurmnt of marbl surfacs. In Optical 3-D Masurmnt Tchniqus V. 1-4 Octobr 21, Gordon, S J, D D Lichti, M P Stwart and M Tsakiri (21) Mtric prformanc of a high-rsolution lasr scannr. In Vidomtrics and Optical Mthods for 3D Shap Masurmnt, January 21, Jlalian, A V (1992) Lasr Radar Systms. Artch Hous: Boston, MA. Kurisak, N, W Ch and T Nakan (21) Applications of 3D masurmnt with ground lasr scannr. In Vidomtrics and Optical Mthods for 3D Shap Masurmnt, January 21, Lichti, D D and B R Harvy (22) An invstigation into th ffcts of rflcting surfac matrial proprtis on trrstrial lasr scannr masurmnts. Gomatics Rsarch Australasia (In prss). Lichti, D D, M P Stwart, M Tsakiri and A J Snow (2) Bnchmark tsting on a thr-dimnsional lasr scanning systm. Gomatics Rsarch Australasia 72: Matthws, L and G Garcia (1995) Lasr and y Safty in th Laboratory. I Prss: Piscataway, NJ. Runn, H, W Nimir and F Krn (21) Application of lasr scannrs to dtrmin th gomtry of buildings.. In Optical 3-D Masurmnt Tchniqus V. 1-4 Octobr 21, Ullrich, A, R Richart, R Schwarz and J Rigl (21) Tim-of-flight basd 3D imaging snsor with tru-color channl for automatd txturing. In Optical 3-D Masurmnt Tchniqus V. 1-4 Octobr 21, 2-9. Wolf, W L (1998) Introduction to Radiomtry. SPI Optical nginring Prss: Bllingham, WA.