Open3D is a project by the Smart Geometry Processing Group in UCL’s Computer Science department. The project aims to provide tools for the crowd-sourcing of large-scale 3D urban models. It achieves this by giving users access to a basic 3D data set and providing an editor enabling them to amend the model and add further detail.
Crowd-sourcing 3D urban models is not new. As we saw in an earlier post on 3D Imagery in Google Earth, Google’s acquisition of SketchUp in 2006 enabled enthusiasts to model and texture 3D buildings directly from satellite imagery. These models could then be uploaded to the 3D Warehouse where they were curated by Google who choose the best models for inclusion in their platform. Despite the enthusiasm of the user community there were limits to the speed of progress and the amount of coverage that could be achieved. In 2012 Google sold SketchUp to engineeting company Trimble after adopting a more automated process relying on a combination of photogrammetry and computer vision techniques. We recently saw similar techniques being used by ETH Zurich in our last post on their project VarCity.
In this context the Open3D approach which heavily relies on human intervention may seem outdated. However, while the kinds of textured surface models that are created using automated photogrammetry look very good from a distance, closer inspection reveals all sorts of issues. The challenges involved in creating 3D models through photogrammetry include: (i) gaining sufficient coverage of the object; (ii) the need to use images taken at different times in order to achieve sufficient coverage; (iii) having images of sufficient resolution to obtain the required level of detail; (iv) the indiscriminate nature of the captured images in the sense that they include everything within the camera’s field of view, regardless of whether it is intended for inclusion in the final model or not. Without manual editing or further processing this can result in noisy surfaces with hollow, blob-like structures for mobile or poorly defined structures and objects. The unofficial Google Earth Blog has done a great job of documenting such anomalies within the Google platform over the years. These include ghostly images and hollow objects, improbably deep rivers, drowned cities, problems with overhanging trees and buildings and blobby people.
The VarCity project sought to address these issues by developing new algorithms and combining techniques to improve the quality of the surface meshes they generated using aerial photogrammetry. For example, vehicle mounted cameras were used in combination with tourist photographs to provide higher resolution data at street level. In this way the ETH Zurich team were able to improve the level of detail and reduce noise in the building facades considerably. Despite this the results of the VarCity project still have limitations. For example, with regard to their use in first person virtual reality applications it could be argued that a more precisely modeled environment might better support a sense of presence and immersion for the user. While such a data set would be more artificial by virtue of the artifice involved in its production, it would also appear less jarringly course in appearance and feel more seamlessly realistic.
In their own ways both VarCity and Open3D seek to reduce the time and effort required in the production of 3D urban models. VarCity uses a combination of methods and increasingly sophisticated algorithms to help reduce noise in the automated reconstruction of urban environments. Open3D on the other hand starts with a relatively clean data set and provides tools to enhance productivity while leveraging the human intelligence of users and their familiarity with the environment they are modelling to maintain a high level of quality. Hence, while the current output for Open3D may appear quite rudimentary compared to VarCity this would improve through the effort of the systems potential users.
Unlike the VarCity project in which crowd-sourcing was effectively achieved by proxy through the secondary exploitation of tourist photos gathered via social media, Open3D seeks to engage a community of users through direct and voluntary citizen participation. In this regard Open3D has a considerable challenge. In order to work the project needs to find an enthusiastic user group and engage them by providing highly accessible and enjoyable tools and features that lower the bar to participation. To that end the Open3D team are collaborating with UCL’s Interaction Group (UCLIC) who will be focused on usability testing and adding new features. There is definitely an appetite for online creation of 3D which is evident in the success of new platforms like Sketchfab. Whether there is still sufficient enthusiasm for the bottom-up creation of 3D urban data sets without the influence of a brand like Google remains to be seen.
For more information on Open3D check out the Smart Geometry Processing Group page or have a look at the accompanying paper here.