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The geoglyphs of San Ignacio - new results from the NASCA project DTM Generation Especially in the geoglyph areas we do have very high accuracy requirements for the DTM. Geoglyphs are usually layed out in fairly smooth terrain. Therefore, even small deviations between them and the surrounding DTM will produce "pumpy" effects in visualization, although the geoglyphs are integrated as 3-D vectors into the DTM a priori.  Figure 3: DTM of San Ignacio in shaded relief representation We have performed tests with automated image matchers, but they did not deliver acceptable results. Therefore, similar as in triangulation, we had to measure the DTM manually on the S9 Analytical Plotter. 94 models were measured in profile mode with 20 m profile spacing, resulting in 296 731 points. In addition 834 breaklines were measured and (up to now) 6 706 vectors belonging to geoglyphs, which were also integrated as breaklines into the DTM. As the other geoglyphs are becoming available they will be integrated as well. Figure 3 represents the complete DTM of San Ignacio with a gross extension of 11 x 6 km2. Orthoimage Derivation and Mosaicking Currently this process is not completed. At the time of the writing of this paper we have generated orthoimages from 21 aerials, which cover about 70 % of the required area. The aerial images were scanned on a Zeiss SKAI with 21 mm pixelsize at the Federal Office of Topography, Wabern, Switzerland.  Figure 4: Current status of orthomosaic The orthoimages and the mosaics were produced with Socet Set. We have orthoimages available at 2 m and 1 m resolution for the whole area, and at 0.5 m and 0.25 m resolution for subareas of special interest. Figure 4 shows the current coverage of the orthomosaic in overview representation. Geolyph Extraction and Visualization The geoglyphs are extracted as 3-D vectors from the individual stereomodels on an Analytical Plotter. Since they appear in a great variety of sizes and forms, partly overlaying each other and partly only barely visible as very faint structures in the images it is important that the interpretation and attributation this is done by an expert, in our case by a project archaeologist. Up to now we have generated 6 706 vectors, but this is an ongoing process which will only be finished in a couple of months (see Figure 5). For visualization and interactive roaming we have the following products available:
Figure 5: Portion of the San Ignacio geoglyphs (yet uncompleted) Currently we use as visualization platforms ERDAS VirtualGIS on an NT machine and SGI SceneViewer. We will also prepare canned image sequences as flyovers and walktroughs, which can be presented by laptops. For real-time visualization we have access to the VisDome facilities of the ETH Zurich, where a large screen stereo display with polarization glasses is available.  Figure 6: Part of the orthomosaic (left) and textured 3-D model (right) of the same area Conclusions We have reported about the status of the second processing phase of our Nasca project. After completion of the Sacramento dataset (Grün, et al., 2000) we have now almost completed the block San Ignacio. The very high data fidelity specifications required the manual measurements of triangulation, DTM and 3-D geoglyphs on Analytical Plotters. The combination of modern analytical and digital (Socet Set by LH Systems for orthoimage and orthomosaic generation) equipment together with up-to-date visualization software resulted in accurate and stunning results. After the implementation of the data on a GIS platform scientists from different disciplines will have a large dataset and tools for analysis at their disposal, which have never been available before. We believe that this will give archaeologists and other experts new and valuable perspectives for their work. It is also interesting to see how much attention such representations find in the general public. Acknowledgements We are grateful for the project funding provided be the AVINA foundation and ETH Zurich, and for the support in scanning the aerial images by Landestopographie (Federal Office of Topography), Wabern, Switzerland. We also acknowledge the contributions of the following people to the San Ignacio part of the project: Nicola d'Apuzzo, Simon Bär, Xioayun Fu, Gillian Grün, Karsten Lambers and Markus Reindel. References
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