João Fradinho Oliveira

3D modelling of laser scanned and photogrammetric data for digital documentation: the Mosteiro da Batalha case study

Advances in both terrestrial laser scanning hardware and photogrammetric systems combined are creating increasingly precise and rich 3D coloured data. In this article we show how computer graphics and visualization techniques have played an important role in real-time visualization, data management, modelling, and data fusion in an increasing number of applications such as surveying engineering, structure analysis, architecture, archaeology and cultural heritage. Specifically, we describe the typical modelling steps involved in the creation of a range of digital documents provided by the 3D digitization company Artescan to customers. We present how these modelling steps were applied in the context of creating digital documents used in the preservation of Mosteiro da Batalha.

PNORMS: platonic derived normals for error bound compression

3D models of millions of triangles invariably repeatedly use the same 12-byte unit normals. Several bit-wise compression algorithms exist for efficient storage and progressive transmission and visualization of normal vectors. However such methods often incur a reconstruction time penalty which, in the absence of dedicated hardware acceleration, make real-time rendering with such compression/reconstruction methods prohibitive. In particular, several methods use a subdivided octahedron to create look-up normals, where the bit length of normal indices varies according to the number of subdivisions used. Not much attention has been given to the error in the normals using such schemes. We show that different Platonic solids create different amounts of normals for each subdivision or bit length in bit-wise compression terms, with different distributions and associated errors. In particular we show that subdividing the icosahedron gives a smaller maximum and mean error than its counterparts Platonic solids. This result has led us to create an alternative to bit-wise compression of normal ids for real-time rendering, where we use a x5 subdivided icosahedron to create 2.5 times more normals than a x5 subdivided octahedron, with less error, and exploit the advantages of absolute normal indices that do not require reconstruction at run-time, whilst still having memory savings of over 83% when using 2-byte indices.We present results using 2-byte indices for a target max error of 1.3° degrees and 4-byte for a max error of <0.1°. We present two hierarchical encoding methods, a fast method which allows one to dynamically encode large sets of modified triangles, useful for task, and a slower but more accurate method that caters for symmetry present in the subdivision solid being used. Different levels of a database allow for different cartoon like shading effects. The advantages of these databases are that they can be re-used for any object, and have studied bounds on the maximum errors of normals for yet to be known geometry such as new objects to be added to a scene. This error bound is also independent of the size and normal distribution of the object that we wish to add. In order to visualize the colour coding distribution of the errors in the normals of large models a simple 1-byte color encoding algorithm was developed.

Payload systems and tracking algorithms for photogrammetric measurement of parachute shape

Parachute systems play a critical role in many science and military missions. Currently, NASA and the U.S. Army air delivery systems programs are evaluating measurement technologies to support experimental and qualification testing of new and modified parachute concepts. Experiments to validate the concept of parachute shape measurement have been conducted in a controlled, indoor environment using both fixed and payload cameras. The paper will provide further detail on the rationale for the experiments, the design of the payload systems, the indoor and outdoor testing, and the subsequent data analysis to track and visualise the shape of the parachute.

The path force feedback belt

In an ideal world, blind people could navigate any new route without training, travel by underground/metro during rush hour without problems, and explore with confidence. Environments can be diverse and dynamic and unfortunately no universal gadget-aid solution yet exists to help navigation. Advances in mobile phone technology and entertainment devices such as the Kinect are allowing for new application scenarios to arise. In this paper, a system that could help interface a person to a wide range of environments is presented. The Path Force Feedback Belt system takes at a fixed rate dual images of the environment using a mobile device, it reconstructs a 3D model of the surroundings, and extracts features such as sidewalk corners, walls, and obstacles. The mobile device then determines which of the force feedback actuators on a 360° belt worn on the waist has to be signaled, hence providing path feedback.