  Digital preservation of Cultural Heritage (CH) sites is crucial to protect
them against damage from natural disasters or human activities. Creating 3D
models of CH sites has become a popular method of digital preservation thanks
to advancements in computer vision and photogrammetry. However, the process is
time-consuming, expensive, and typically requires specialized equipment and
expertise, posing challenges in resource-limited developing countries.
Additionally, the lack of an open repository for 3D models hinders research and
public engagement with their heritage. To address these issues, we propose
Tirtha, a web platform for crowdsourcing images of CH sites and creating their
3D models. Tirtha utilizes state-of-the-art Structure from Motion (SfM) and
Multi-View Stereo (MVS) techniques. It is modular, extensible and
cost-effective, allowing for the incorporation of new techniques as
photogrammetry advances. Tirtha is accessible through a web interface at
https://tirtha.niser.ac.in and can be deployed on-premise or in a cloud
environment. In our case studies, we demonstrate the pipeline's effectiveness
by creating 3D models of temples in Odisha, India, using crowdsourced images.
These models are available for viewing, interaction, and download on the Tirtha
website. Our work aims to provide a dataset of crowdsourced images and 3D
reconstructions for research in computer vision, heritage conservation, and
related domains. Overall, Tirtha is a step towards democratizing digital
preservation, primarily in resource-limited developing countries.
