LPS Instrumental in 3D modeling of the Acropolis

12 March 2009, 2:56am

Norcross, GA — ERDAS announces that LPS was recently selected and utilized for a significant project to create 3D models of the Acropolis in Greece. LPS is an integrated suite of photogrammetry software tools for generating terrain models, producing orthophotos and extracting 3D features.

This project, called the “Development of GIS at the Acropolis of Athens” was financed by the European Union and the Government of Greece, and supervised by the Acropolis Restoration Service, Hellenic Ministry of Culture. The partners in this project are ELLINIKI PHOTOGRAMMETRIKI Ltd (ELPHO), Athens and GEOTECH O.E., Athens. GEOINFORMATION S.A., the authorized ERDAS distributor in Greece provided photogrammetric support to ELPHO for this project.

The created GIS incorporated large-scale orthomosaics for the Acropolis’ walls, top view of the site, and walls along the rock. To develop the GIS, the project included field measurements for the generation of a polygonometric network and terrestrial laser scanning of the walls along with the Erechtheion monument, image acquisition, orientation, DSM generation and orthorectification. The Leica HD3000 was one of the pieces of hardware used for the laser scanning of Erechtheion.

“This project illustrates the potential of combining photogrammetry and state-of-the-art geodetic techniques (laser scanning) for an accurate 3D modeling of cultural heritage sites,” said Vassilios Tsingas, Project Manager, ELPHO Ltd. “LPS was an integral part of the project, ensuring the utmost accuracy, processing imagery from a wide variety of sensors.”

Once all the data was captured, LPS performed a bundled adjustment, using a dense network of control points measured with accuracy less than two millimeters. The 1557 aerial images of the top view, captured with a balloon from a height of 22 m above the ground, were oriented as one photogrammetric block using bundle adjustment triangulation. The 2250 images of the wall facades, captured with balloon as well; from a distance of 5 m, creating 34 photogrammetric blocks, which were oriented separately. To recreate the inner geometry of the utilized cameras, initially 20 images of strong geometry (converging images with different k rotation) were oriented using self - calibration bundle adjustment.

The exterior orientation of the images was carried out with LPS, based on automatic and semi-automatic techniques (tie point measurement) followed by stereoscopic checks. The aerial images of the top view of the Acropolis were separated into four blocks and oriented using bundle adjustment triangulation.

For the side views of the walls, individual well-defined points from the intensity maps of the laser scanner were selected and used as ground control in the bundle adjustment, ensuring a proper registration of the images against the laser data.

The digital terrain model of the top view was generated with automatic terrain extraction techniques at a resolution of 0.02m and 0.01m, for the top view and the walls respectively. The results were corrected manually using suitable collection techniques, improving the final quality.

“Photogrammetry and terrestrial laser scanning are important in the geometrical and textural documentation of archaeological monuments,” said Thomas Bayer, Vice President, EMEA, ERDAS. “Automating precision measurement, LPS is a leading photogrammetric solution, increasing productivity while ensuring high accuracy.”

For more information about ERDAS, please call +1 770 776 3400, toll free +1 877 GO ERDAS, or visit www.erdas.com.

ERDAS

Geo: International