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DEFORMATION MEASUREMENT TERM PRESENTATION. By Prepared Ahmet Turan İşbeceren. Deformation Measurement Spring - 2012. DEFORMATION MEASUREMENTS AT HISTORICAL BUILDINGS WITH TERRESTRIAL LASERSCANNERS. Contents : 1. Introduction 2. Laser Scanning System Imager
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DEFORMATION MEASUREMENT TERM PRESENTATION ByPrepared Ahmet Turan İşbeceren DeformationMeasurementSpring- 2012
DEFORMATION MEASUREMENTS AT HISTORICAL BUILDINGS WITH TERRESTRIAL LASERSCANNERS Contents: 1.Introduction 2.LaserScanningSystemImager 2.1.Hardware and Software 2.2.Data Acquisition, RegistrationandGeoreferencing 3.Objectsto be Scanned 4.Data Processing of theLaserscans 4.1.Recording of thePresentState 4.2.EvaluationandResults 5.Summaryand Outlook DeformationMeasurementSpring- 2012
1.Introduction • - Whataredisadvantages of total station in measurement of HistoricalBuilding? • - Properties of HistoricalBuilding • Why do weneedtheLaserscanners? • Whatareadvantages of laserscanners in deformationmeasurement? DeformationMeasurementSpring- 2012
2.LaserScanningSystemImager The systems available on the market vary very strongly withrespect to their qualification for outside or inside measurements.For outside measurements the Mensi GS100 is a suitableinstrument, due to its large scan distance of up to 200 m (overscan). DeformationMeasurementSpring- 2012
2.2.Data Acquisition, RegistrationandGeoreferencing An important component of laser scanning systems is thesoftware, with features summarized in Tab. 2.
The semi-automaticcomputation is carried out subsequently in the software Z+FLaserControl and/or Light Formed Modeller (LFM) (see Fig.2).
3.Objectsto be Scanned Churchesconsists of bran, peat and watt sand. Long-termandshort-termchanges in the ground, which result fromgroundwater setting,led to inclinations of the walls. The mass distribution and themisalignment of the churches is not known. A precise measurement of thevolume body is needed to calculate the actual statics, thecurrent mass distribution, and the forces. Laser scanners aresuitable for the complete data acquisition.
Description of the Object St. Johannis, Cathedral inMeldorf • The church stands on aembankment approx, • - 14 m abovemeansea level and was built in the 13th century. • In 1490, the late-Gothic “Suederhalle” was built instead of a side aisle. • - But themovement of the “Suederhalle” in the south direction could not be stopped. Fig. 3/4: Pictures of St. Johannis in the year 1820 and today(Lambrecht, 2003)
4.Data Processing of theLaserscans 4.1.Recording of thePresentState • 11 fixedpointswerefixed in theinterior of thechurch • - 43 targetsweremeasuredfortheregistration of theindividual • scanswiththe total station • Each of the 23 scans in total took 7 minuteswith 1.2 millionsurveyedpoints. • Theregistrationandgeoreferencing of theindividualscanswereaccomplished in thetworelatedprograms Z+F LaserControland LFM Modeller. • Finallyallscanswereregistered in the software LFM Modeller, sothat a homogeneous model of thechurchwascreated as a pointcloud
4.1.EvaluationandResults • * For the as-built documentation of the present state the registeredpoint clouds were processed with the software LFM Server andAutoCad. • * The LFM Server software allows the export of selected point clouds to AutoCad. • * In AutoCad the final construction including the dimensioning is done manually.
In order to detect the change in Meldorf, the areas with thegreatest changes are observed: the vaults in 14 meters aboveground (Fig.8). If the inclination of the sidewalls keeps oncontinuing, the vaults will deform.
Process of DeformationMeasurement: • For the observation of long-term deformation with laser scandata the following indirect methods could be used: • • Comparison of gridpoints • • Comparison of linear structures like cuts • • Comparison of surfaces – in the simplest case a plane • * The first step in each case is the transformation of the pointcloud into the same coordinate system, • * In the second case cuts could be generated, • * The simplest case of a surface comparison could be usingplanes.
Thereforethetriangulationwascarried out with the software RapidFormXOScan by Inustech.The algorithm used by RapidForm is similar to the TRIADSalgorithm, with a region growing algorithm based on triangleswith one given initial triangle. The meshed triangles fromRapidForm are displayed in Fig. 9 below as a smooth surface.
The changes of the normal vector of the plane was used as a deformationcriterion. The deformation of the Europepassage was below 5 mm and the observation period was over 4months, so a change could not be detected.
5.Summaryand Outlook With the laser scanner it is possible to create very quickly anas-built documentation and a construction of simple cuts. Theevaluation took place within one day. As a result 4 slices atdifferent levels were produced parallel to the z-plane and 7slices parallel to the x- and y-plane. The generation of cuts and orthophotos is very elegant with theLFM software, the duration is, however, also clearly higher. During the computation of deformations, the use of surfacesappears promising. Not single points but the object as a wholeare considered. Just in this field improvements are still to beexpected in next time. The use of third party software is vitalhere. The complex question formulations are solved only byspecific software programs, and these are not integrated in theinternallaserscannerprocessing software yet.
