Introduction

As part of the Artest project, a mini-project carried out at the National University of Mongolia aimed to create a digital model of an object using various survey technologies, including range-based and image-based methods.

The object under study was the archaeological artifact AAT176, a “Lamp-shaped terracotta container” dating back to the Xiongnu era (3rd century BCE to 1st century CE), discovered in one of Mongolia’s tombs, specifically Burial 97 near Arkhangai Tamiriin Ulaan Khoshuu, in 2005.

Survey and Image-Based Techniques

Digital survey

To create the model using photogrammetric techniques, the following equipment was used:

•          A Nikon 7 Pro camera with a tripod, allowing for adjustable settings (brightness, exposure, aperture, etc.) to capture highly detailed images.

•          A lightbox with white lights and a circular rotating platform for controlled rotation of the vase. This setup enabled consistent and precise photography from various angles.

The project’s primary goal was to produce an accurate 3D model of the vase, virtually preserving its shape and decorations for archaeological study purposes.

During the photography sessions, the vase was placed on the rotating platform within the lightbox, ensuring a controlled environment with uniform lighting and minimized reflections. Photographs were taken with an overlap between successive images and with different visual cones, lateral, from above and in perspective.

Elaboration

The collected images were processed using two main software tools:

1. Agisoft Metashape: a photogrammetry software employing advanced algorithms to generate 3D models from a series of photographs. The process includes:
   • Image alignment: Identifying common points among photos to create a sparse point cloud.
   • Dense point cloud creation: Developing a detailed representation of the model.
   • Mesh generation: Converting the point cloud into a continuous 3D surface.
   • Texturing: Applying the original images onto the surface to produce a realistic model.
2. Autodesk Recap Photo:

Another photogrammetry software, particularly designed for integration with other 3D design tools offered by Autodesk. The process also includes image alignment, point cloud generation, and 3D model creation. Recap Photo is noted for its simplicity and integration with cloud systems, accelerating processing times.

At the end of processing, two 3D models of the vase were created one using Metashape and the other using Recap Photo allowing for a final comparison.

Comparison

The comparison focused on both quantitative aspects (e.g., file size in KB, number of photos used per software, vertices, and faces) and qualitative aspects, including:

• Geometric accuracy: The model created with Metashape demonstrated higher precision in details, such as the vase’s decorative motifs.
• Processing time: Recap Photo required less processing time, albeit with a slight loss of detail compared to Metashape, which demanded longer processing durations.
• Ease of use: Metashape requires more expertise, while Recap Photo is intuitive and user-friendly, even for beginners.

The comparison highlighted the strengths and limitations of each software, offering insights for optimizing future digital survey projects.