Documentation and virtual reconstruction of historical objects in Peru damaged by an earthquake and climatic events

This paper deals with the possibilities of creating a 3-D model and a visualization technique for a presentation of historical buildings and sites in Peru. The project Nasca/CTU is documenting historical objects by using several techniques. This paper describes the documentation and the visualization of two historical churches ( San Joseand San XavierChurches) and the pre-Hispanic archaeological site La Ciudad Perdida de Huayuri (Abandoned town near Huayuri) in Nasca region by using photogrammetry and remote sensing. Both churches were damaged by an earthquake. We use different process for the documentation of these objects. Firstly, PhotoModeler software was used for the photogrammetric data processing of the acquired images. The subsequent making models of both churches were different too. Google SketchUp software was used for the San Jose Church and the 3-D model of San Xavier Church was created in MicroStation software. While in the modelling of the “Abandoned town” near Huayuri, which was destroyed by a climatic event (El Nĩ no), the terrestrial photogrammetry, satellite data and GNSS measurement were applied. The general output of the project is a thematic map of this archaeological site; C14 method was used for dating.


Introduction
Around Nasca and Palpa city in Peru there are many interesting historical objects which are suitable for documentation (Eisenbeis et al., 2005).In HTW Dresden (University of Applied Sciences, Germany) the project Nasca was started in 1995 (Richter, 2007).The main goal was to prolong the scientific work of Dr. Maria Reiche which focused on the documentation and investigation of geoglyphs in the Nasca region and preservation of other cultural heritage in digital form (Musílek et al., 2001).For that reason, a NascaGIS application was developed.The primary requirement of any GIS application is the data.The photogrammetric approach is one of the most practical solutions to capture such data.Not only geoglyphs, but all valuable historical objects are documented, such as buildings, petroglyphs and selected archaeological sites.The Nasca/CTU project has cooperated with the Nasca project in HTW Dresden since 2004.Within the project, four German-Czech expeditions to Peru have been performed focusing on Nasca region and other areas.The famous Nasca Lines are the core of the Nasca project.We concentrated on other lesser-known objects of interest -endangered monuments like churches or archaeological sites, frequently prone to destruction.San Jose Church, San Xavier Church, hacienda de La Peňa or the archaeological site "Abandoned town near Huayuri" can be mentioned.Some of these objects were destroyed by an earthquake (churches), while others, mainly archaeological sites, were destroyed by climatic events (El Niño).Data of historical objects or sites was acquired for the documentation process during the expeditions to Peru in 2008, 2010 and 2012.This paper deals with three of them: San Jose and San Xavier Churches and an abandoned town near Huayuri.These three objects are historically interesting and adequate from our point of view as well as they are suitable for our technological possibilities in Nasca region.6 added as a layer together with contour lines created from DEM to the thematic map (Fig. 4).14

San
The results of the work are the following: the thematic map the "Abandoned town" near 15 Huayuri in Peru, the 3D area view in vrml format, video demonstration of flying over the 3D 16 model, the kml file for Google Earth (Fig. 4).17 model, the kml file for Google Earth (Fig. 4).17 6 processed satellite data, which has been transformed to geodetic frame by using of measured 9 GNSS points.The final model of the "Abandoned town near Huayuri" was placed into 10 Peruvian coordinate system PSAD56.A newly prepared DEM from Terra/Aster stereo 11 satellite images was used for satellite data processing with resolution of about 15 m, based on 12 GNSS measurement of necessary control points.Good visible objects were vectorised and 13 added as a layer together with contour lines created from DEM to the thematic map (Fig. 4).14 The results of the work are the following: the thematic map the "Abandoned town" near 15 Huayuri in Peru, the 3D area view in vrml format, video demonstration of flying over the 3D 16 model, the kml file for Google Earth (Fig. 4).17 found under the church.Documentation work was conducted in 2010.The second object, San Javier Church is a typical object, which represents some of the most outstanding examples of baroque architecture in the region.Built in 1745-1746, it is a cultural heritage associated with the period of Spanish colonization.The Church is dominated (Fig. 2) by two cylindrical towers in its front part and two sacristies in the rear.It is located 35 km northwest from Nasca City, in a small village (ϕ = 14 • 39 38 S, λ = 75 • 11 26 W).Detailed photogrammetrical documentation was made during expedition in 2008.The churches are not used for religious ceremonies because of the poor technical condition of the building caused by severe earthquakes; the big one in 1940 and some others turned the churches into ruins.Both churches are listed in the World Monuments Fund watching list; this association is engaged in raising funds for repairing major historical monuments.The Jesuit Churches of San José and San Javier are in need of integrated plans for conservation and revitalization in order to ensure their survival for future generations.3-D documentations, that we made were simplified and placed in Google Earth.The last object is La Ciudad Perdida de Huayuri (Abandoned town near Huayuri) near Palpa village in a hidden valley.The valley is oriented northeast from the Santa Cruz River, at Huayuri village.The abandoned town is a pre-Columbian town in Peru built in the late medieval period.Its period is dated sometime between the years 1000 and 1450 but it is very hard to say its exact origin and perishing.It is assumed that it was developed during the Huari culture decline and finished with the rise of Inca culture.The town remains are spread in the valley at about 15 hectares area.There are remains of various building walls on the bottom of the valley and on the slopes around.The found buildings are close to each other with a very small space between them which is typical for local human settlement architecture.The building structure of the ruins had only living purposes; objects that could serve some other purposes -for example religious or economical -were not found.At present there is very little information about the "Abandoned town", its inhabitants, and their customs.Most information comes from natives and partly from the previous research undertaken in 1975 and 1984.There was also the project PAHUAY -proyecto archeologico de Huayuri since 2002 to 2005.The project was done in cooperation with University of Pittsburgh and Peruvian universities.

Pre-processing of photogrammetric data
From the photogrammetric point of view, it is necessary to use a calibrated camera for the capturing of image data before creating the 3-D model.In our case the calibration was performed by software PhotoModeler Scanner (PMSC).PMSC is intended for noncontact 3-D measurement.It is based on convergent multi-photo photogrammetry method.This means the 3-D coordinates the points of an object which are computed at least from two convergent, appropriately configured images.PMSC can be used for creating 3-D model, which is possible to export to other software's like CAD systems.The extension of the PMSC can acquire from images point cloud (similarly as laser scanner).In this effort, we used the 3-D documentation of small archaeological funds like funeral ceramic container or other objects.From the created 3-D model, it is possible print replicas on 3-D printer.It is advantageous, because any export of artefacts is prohibited.For a model creating with its real scale, it is necessary to know the object dimensions.There are two approaches: by using control points or by measurement of distances on the object.We used both of these techniques: (a) in the case of archaeological area "Abandoned town" the GNSS GIS instrument was used (our own created base stations in Palpa and Nasca has been used with combination with rover instrument) with a typical accuracy of 60 cm (b) precise distances measurements on churches ruins.Our acquisition of photogrammetric images and other metric information was simple, because we cannot normally afford more accurate measuring equipment (total station or laser scanners) from financial and administrative reasons in other countries.For this reason, our conducted research was based on existing simple and low cost methods of 3-D documentation in our Laboratory of photogrammetry.All objects were photographed by calibrated digital camera from different stations using convergent photogrammetric technology.Dimensions of objects were determined by measuring tape and laser distance meter.In the case of the both churches, a 3-D model was created from appropriate pictures.Of course, documentation of historical objects is not only a metric survey -other information like historical data, architectonical analysis etc. had to be included to the basic measurement.In developing countries, there is no documentation for most of the lesser-known but still valuable objects and they are of marginal interest (Richter and Teichert, 2008).

San Jose Church
Various methods were used for processing and visualisation of objects of interest.We focused on a simple and affordable means.The program Google SketchUp was used for creating the 3-D model of San Jose Church (Fig. 1a); it is the software for creating, modification and 3-D data sharing (Fig. 1b).The present model can be linked through the 3-D gallery of objects in application Google Earth (GE), which is a virtual globe providing maps and geo-information.The application GE allows viewing the Earth on satellite images mosaic with variable resolution.The advantage of software SketchUp is that it works with the GE application.It is very easy to insert a 3-D model into the GE application.SketchUp is simple software for 3-D models and it has no direct functions for object accuracy evaluation.This can be made by comparing of the measured lengths on an object and the same lengths measured on the model.Differences of compared lengths ranged between 0-19 cm in our project.The average value of the difference = 7.8 cm, standard deviation of difference using the formula (1) is σ = 10.0 cm ( is difference and n is number of measurement).

San Javier Church
The other possibility to create a 3-D model is the appropriate but arbitrary CAD software.MicroStation software was used for creating the model of San Javier Church based on basic photogrammetric processing in PhotoModeler.MicroStation is one of the most popular CAD products, which is used to create 2-D and 3-D drawings.Model accuracy in PhotoModeler software is given by value RMS (residual error).RMS indicates differences between the positions of a point specified by a user and the same point, which the program calculates (the program executes a global adjustment of position of all calculated points).The accuracy of this model reaches approximately 1.5-4.9pixels.The absolute accuracy depends on pixel size; by our project reaches 1-2 cm.Original photo of San Javier Church is on Fig. 2a.Its 3-D model is in this case without textures, only coloured (Fig. 2b).The visualization is focused on the shape and dimension of the graphical model output for documentation and it is suitable for visible study, for architectural designs or for reconstruction.
Our output is a simplified model of the San Javier Church (Fig. 2b).The accuracy of this model has been defined by the lengths.The lengths in the model were measured and compared with the actual lengths on church.Several measures were selected.From these distance differences the standard deviation of twin measurement were calculated (it reaches 4 cm).

"Abandoned town"
A different approach in case of "Abandoned town" archaeological site was used.It is a very large area for close range photogrammetry.The distances were measured on ruins only for control.Object and control points were measured by GNSS with standard deviation of 55 cm (base -rover GIS GNSS instrument), which was sufficient for creating of thematic map of this big area (about 15 hectares).The photogrammetric processing combines both terrestrial (Fig. 3b) and satellite images (Guidi et al., 2009).Satellite data was made on demand (new data especially for this project) by the GeoEye-1 satellite with spatial resolution 0.5 m in panchromatic and 1.64 m resolution in multispectral imagery.Special procedures for image sharpening and other filtering were used (Fig. 3a).Using PhotoModeler software, a partial model of the abandoned town uncovered by the previous archaeological research has been made.This model was placed into the area with help of the GNSS points measured during the expedition.An important part of the whole area was processed from adjusted and pre-processed satellite data, which has been transformed to geodetic frame by using of measured GNSS points.The final model of the "Abandoned town near Huayuri" was placed into Peruvian coordinate system PSAD56.A newly prepared DEM from Terra/Aster stereo satellite images was used for satellite data processing with resolution of about 15 m, based on GNSS measurement of necessary control points.Good visible objects were vectorised and added as a layer together with contour lines created from DEM to the thematic map (Fig. 4).The results of the work are the following: the thematic map the "Abandoned town" near Huayuri in Peru, the 3-D area view in vrml format, video demonstration of flying over the 3-D model, the kml file for Google Earth (Fig. 4).
It is not possible or very complicated to use other expensive instruments due to financial and administrative reason (Chiabrando et al., 2011).In consequence, calibrated digital cameras and other above mentioned instruments are very effective and they are preferable for small projects (Richter, 2007).Model visualization was made by using animation methods (Pomaska, 2011); VRML browser and 3-D model of San Jose and San Javier churches have been published on the web through Google Earth.The photogrammetric processing was made by PhotoModeler software and the subsequent modelling was made by SketchUp or MicroStation.SketchUp software was used also for textures; there are possibilities to present the model on the internet in 3-D Gallery (Pavelka et al., 2011)."Abandoned town", the VHR satellite image was used with success (Richter and Teichert, 2008;Pavelka et al., 2010).
The last part of the investigation was experimental dating by radiocarbon analysis of C 14 .Discovered fireplace remnants in one building were analysed.The result gives two periods (with one sigma range): 1287-1328 AD or 1337-1391 AD (Světlík, 2012).It can be approximately date of the settlement destruction.Of course, it is only one measurement, but it shows possibilities of low cost survey.

Conclusions
The aim of our study was to show the possibility of easy and non-expensive geometric object documentation and visualisation, which can be used for popularisation and basic reconstruction planning.The 3-D models of the three objects of interest were created through photogrammetric and satellite images.No special instruments were used, only calibrated camera, laser distance meter, tape, software and GNSS instrument.The visualization of the objects of interest can be either a basis for a reconstruction or for simple advertising of the historical objects in areas, where a financial level is not at the accurate targeting geodetic methods or laser scanning.We can conclude that the usage of image data can create outputs of high quality.In some countries documentation and subsequent reconstruction of historical buildings are neglected activities, which can lead to the irreversible loss of such monuments.In addition to the age and a little care taken of historical monuments, there are also threats of war conflicts, nature disasters or vandalism.Recent events in Syria or other countries indicate that this is a real problem.Many foreign projects are focused on these areas, and the Nasca/Peru project is one example of this.
Edited by: K. Tokeshi Reviewed by: B. Teichert and two anonymous referees Jose Church is situated in the El Ingenio region approximately 30 km northwest of Nasca City (ϕ = 14 • 40 15 S, λ = 75 • 07 44 W, Fig. 1).The church was built in 1744 in the baroque style.There are two wooden towers covered by plaster, which dominates the church.Twelve crypts were Published by Copernicus Publications on behalf of the European Geosciences Union.K. Hanzalová and K. Pavelka: Historical objects in Peru damaged by an earthquake and climatic eventsHuayuri in Peru, the 3D area view in vrml format, video demonstration of flying over the 3 model, the kml file for Google Earth (Fig.4).

Figure 1
Figure 1.a: Original image of San Jose Church.Images taken by calibrated camera were use for creating of the 3D model for Google Earth (Fig.1.bright; Hanzalová and Čumpelík, 2011

18Figure 1 Fig. 1 .
Figure 1.a: Original image of San Jose Church.Images taken by calibrated camera were used 19 for creating of the 3D model for Google Earth (Fig.1.bright; Hanzalová and Čumpelík, 2011).20

18Figure 1
Figure 1.a: Original image of San Jose Church.Images taken by calibrated camera were us 19 for creating of the 3D model for Google Earth (Fig.1.bright; Hanzalová and Čumpelík, 201 20

10 Figure 4 :
Figure 3.a: "Abandoned town" near Huayuri.GeoEye-1 satellite data (left) after 2 application of filtering.Fig.3b.(right) is an example of terrestrial image.3 4 The last part of the investigation was experimental dating by radiocarbon analysis of C 14 .5Discovered fireplace remnants in one building were analysed.The result gives two periods 6 (with one sigma range): 1287-1328 AD or 1337-1391 AD(Světlík, 2012).It can be 7approximately date of the settlement destruction.Of course, it is only one measurement, but it 8 shows possibilities of low cost survey.9