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  INTRODUCTION IN ARCHITECTURAL PHOTOGRAMMETRY Author: Stud. Ana ALEXANDRUScientific Coordinator: Associate Professor PhD. Gabriel POPESCU University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti Blvd,District 1, 011464, Bucharest, RomaniaCorresponding author email: alexandru_ana2000@yahoo.com  Abstract  The work suggests the theoretical first step on close new-range photogrammetry, in general, and architectural  photogrammetry, in particular. The purpose is that to promote the new geomatics technologies, very useful for our world, specialists but non-specialists too, to solve many civil engineering works, old buildings, historic bridges,castles, feudal fortress, archeological sites, historic and art monuments, to protect them, to restore them in order to point out the real, srcinal values of a people, his works, his true achievements. A complete approachment of analytical and digital photogrammetric methods using CAD systems, combined withlaser scanning and other non-destructive research techniques of remote sensing has the purpose of finding the best  solution for surveying, inventorying, monitoring, restoration and conservation of space-objects. The benefit of combination closing-range photogrammetric methods with others geomatics and geophysics researches is that it  provides a solid technical documentation of a space-object as a basis for technical rehabilitation or restoration planning, a total inventory, both quantitative and qualitative. In the framework of our research, we are going to talk about photogrammetric work in general, but alsorepresentation techniques of space object obtained by photogrammetric methods in close-range photogrammetry, in particular. The combination and fusion of different data sources (RGB, NIR and thermal IR images) allows to usachieving goals as localization, visualization and analysis of anomalies in contemporary architecture and, in order to that, planning restore buildings where it is necessary.  Key words:  Architecture, Close-Range Photogrammetry, Photogrammetry, Surveying. INTRODUCTION For a good definition of the Photogrammetryconcept, it is necessary for us to refer theRemote sensing too.We consider that we need aerial photography for having a good plotting of different objects: buildings, castles, fortress,archeological sites, settlements, historic andart monuments etc.Unlike the map, which is a vertical projection of a landscape elements on a zerolevel plane surface, the photogram is theimage into a plan of these elements, seenfrom a space-point.In photogrammetry, we can draw uptopographic maps with level curves, basedon measurements and data, obtained fromaerial photos, with analogical instruments,optical or/and analytical computers.Similarly, the principles of topographicmeasurements accuracy are being applied onclose range photogrammetry, for representing the objects which cannot bestudied other ways, or whose studying isvery difficult on other ways, to register deformations of measured value inengineering models.  Compared with aerial photogrammetry, close range photogrammetry and particularly  architectural photogrammetry isn’t limited to vertical photographs, withspecial cameras. The methodology of terrestrial photogrammetry has changedsignificantly and various photographicacquisitions are widely in use. New technologies and techiques for dataacquisition (CCD cameras, Photo CD photoscanners), data processing (computer vision), structuring and representation(CAD, simulation, animation, visualization)and archiving, retrieval and analysis (spatialinformation systems) are leading to novelsystems, processing methods and results.The Close-Range Photogrammetry (CRP)relies on the reconstruction of the objectsimultaneously from several images fromdifferent and best possible perspective, toensure a suitable geometry of intersectingrays.So that, close-range photogrammetry ismeant to be in that situation when thedistance (range) from the camera to theobject of interest is somewhere from 1 m toaprox.300 meters.The improvement of methods for surveyinghistorical monuments and sites is animportant contribution in recording andmonitoring of cultural heritage , in preservation and restauration of anyarchitectural or cultural monument, objector site, as a support of architectural,archeological and other art-historicalresearch. Images Processing Close range photogrammetry is a techniquefor getting geometric information (position,size and shape) of any object, that wasimaged on photos before.To achieve a restitution of a 3D point, it isnecessary to have the intersection between atleast two rays (from the camera to the objectyou are going to take the photo) in space.If more than two rays are available ( it was possible to have more than one photo of theinterested object), the solution is that we willhave a better restitution of the object or themonument. That solution provides from allthe measurements and, in that situation, itwill be more accurate. Single Images A very common problem is that we knowthe shape and position of an object’s surfacein space (digital surface model), but we areinterested in having details on that surface: patterns, texture, additional points etc. Inthat case, a single image restitution can beappropriate to obtain the fotogramma. a)When there are known camera parameters and exterior orientation.In that case, there is necessary to know theinterior orientation of the camera andcamera’s position and orientation. That so,we can reckon the points, by intersection of rays from camera with the surface whoseshape and position we know. Interior orientation does not mean only thecalibrated focal length and the position of the principal point, but also the the polynomial coefficients for describing lensdistortion (if the photo does not providefrom a metric camera).If the camera position and orientation isunknown at least 3 control points on theobject (points with known co-ordinates) are  necessary to compute the exterior orientation. b)When there are unknown camera parameters.This is a very frequent problem inarchitectural photogrammetry. The shape of the surface is restricted to planes only and aminimum number of four control points intwo dimensions have to be available. Therelation of the object plane to the image plane is described by the projective equationof two planes:   1 2 31 21 2 31 2 11 a x a y a X c x c yb x b y bY c x c y + +=+ ++ +=+ + Where X and Y are the co-ordinates on theobject's plane, x and y the measured co-ordinates on the image and a i ,b i , c i the 8 parameters describing this projectiverelation, the measurement of a minimum of 4 control points in the single photo leads tothe evaluation of these 8 unknowns (a 1 , a 2 ,a 3 , ... , c 2 ) . As a result, the 2D co-ordinates of arbitrary points on this surface can becalculated using those equations. This isalso true for digital images of facades.Digital image processing techniques canapply these equations for every single pixeland thus produce an orthographic view of the object's plane, a so-called orthophoto or orthoimage.  Stereographic Processing If its geometry is completely unknown, asingle image restitution of a 3D object isimpossible. In this case, the use of at least 2images is necessary. According to thestereographic principle, a pair of stereoimages can be viewed together, which produces a spatial (stereoscopic) impressionof the object. This effect can be used toachieve a 3D restitution of the facades.Using stereo pairs of images , arbitraryshapes of a 3D geometry can bereconstructed as long as the area of interest is shown on both images. Thecamera directions should be almost parallel to each other to have a goodstereoscopic viewing.Metric cameras with well known andcalibrated interior orientation andnegligible lens distortion are commonlyused in this approach. To guarantee goodresults, the ratio of stereo base (distance between camera positions) to the cameradistance to the object should lie between1:5 and 1:15.Results of stereographic restitution can be:2D-plans of single facades, 3D-wirefameand surface models, lists of co-ordinates,eventually complemented by their topology (lines, surfaces, etc). Bundle Restitution In many cases, the use of one single stereo pair will not suffice to reconstruct acomplex building. Therefore, a larger number of photos will be used to cover anobject as a whole. To achieve ahomogenous solution for the entire building and also to contribute additionalmeasurements, a simultaneous solution of all photo's orientation is necessary.  Another advantage is the possibility to perform an on-the-job calibration of thecamera. This helps to increase theaccuracy when using images of anunknown or uncalibrated camera. So thisapproach is not any more restricted tometric or even calibrated cameras, whichmakes the application of photogrammetrictechniques a lot more flexible. It is alsoadjustable concerning the geometry of camera positions, meaning one is notforced to look for parallel views andstereo pair configuration. Convergent,horizontally, vertically or oblique photosare now well suitable. Combination of different cameras or lenses can easily bedone.Here we have examples of differentconfigurations for bundle solution, for acircle building or paralelipipedic one.The strategy of taking photos is that each point to be determined should beintersected by at least two rays of satisfactory intersection angle. This angledepends only upon the accuracyrequirements. Additional knowledge of e.g. parallelism of lines, flatness of surfaces and rectangularity of features inspace can be introduced in this process andhelps to build a robust and homogenoussolution for the geometry of the object.The entire number of measurements and thefull range of unknown parameters arecomputed within a statistical least squaresadjustment. Due to the high redundancy of such a system it is also possible to detect blunders and gross errors, so not onlyaccuracy but also reliability of the resultwill usually be increased.Bundle adjustment is a wide spreadtechnique in digital architectural photogrammetry of today. It combines theapplication of semi-metric or even non-metric ( amateur  ) cameras, convergent photos and flexible measurements in acommon computer environment. Becauseof the adjustment process, the results aremore reliable and accurate and very oftenreadily prepared for further use in CADenvironments.Results of bundle restitution are usually3D-wireframe and surface models of theobject or lists of co-ordinates of themeasured points and their topology (lines,surfaces, etc) for use in CAD andinformation systems. Visualizations andanimations or so-called photo-models (textured 3D-models) are also commonresults. Usually the entire object isreconstructed in one step and the texturefor the surface is available from srcinal photos. Photogrammetric Architectural SurveyMethods For simple photogrammetric documentationof architecture, simple rules which are to beobserved for photography with non-metriccameras have been written, tested and published by (Waldhaeusl & Ogleby,

SGHU2922_Lecture5

Sep 11, 2019

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Sep 11, 2019
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