The presented results demonstrate the effectiveness of our volumetric reconstruc-tion algorithm for planetary nebulae. Given two input images at different wave-lengths, we can recover both the 3D distribution of emitting gas as well as the density of dust particles in axis-symmetric nebulae. Our physically-based recon-struction and visualization algorithms simulate emission, absorption and scatter-ing.
The quality of the reconstruction results is limited by the input images for any recovered gas or dust data. It is important that the input images are well aligned and have similar resolution in order to obtain accurate reconstruction results. Fur-thermore, any deviation from axis-symmetry in the real nebula affects the recon-structed volumes.
Because we assume axial-symmetry the reconstruction results depend on the in-clination angle of the symmetry axis and the projection direction. The best quality is obtained if the symmetry axis is parallel to the image plane.
While our current approach incorporates only two images at different wavelengths and assumes that the image of one wavelength is not at all effected by the dust, fur-ther extension of the algorithm could incorporate more images at different wave-lengths to increase the stability of the optimization. In addition, it is not necessary to assume that one image is completely unaffected by scattering and absorption.
7.6 Discussion and Future Work 93
Figure 7.12: Reconstructed He2-320 rendered at an inclination angle of 50◦and 75◦. By viewing the nebula at different inclination angles, we can derive a better insight in its 3D distribution.
As long as the scattering and absorption coefficients are sufficiently different the ionized gas and the dust distributions could be recovered if optimized simultane-ously.
Besides the application in astronomy, it is promising to investigate the perfor-mance of the proposed volumetric reconstruction algorithm in the context of med-ical imaging, where scattering and absorption are the main effects when illumi-nating through biological tissue.
94 Chapter 7: 3D Reconstruction of Gas and Dust in Planetary Nebulae
Part IV
An Augmented Reality Application for Educational
Astronomy
Chapter 8 Augmented Astronomical Telescope
Anyone who has gazed through the eyepiece of an astronomical telescope knows that, with the exception of the Moon and the planets, extra-solar astronomical ob-jects are disappointing to observe visually. This is mainly due to their low surface brightness, but also depends on the visibility, sky brightness and telescope aper-ture. In this chapter we describe a system which projects images of astronomical objects (with focus on nebulae and galaxies), animations and additional informa-tion directly into the eyepiece view of an astronomical telescope. As the telescope orientation is queried continuously, the projected image is adapted in real-time to the currently visible field of view. For projection, a custom-built video projection module with high contrast and low maximum luminance value was developed.
With this technology visitors to public observatories have the option to experience the richness of faint astronomical objects while directly looking at them through a telescope.
8.1 Introduction
Since its beginning, mankind has always been fascinated by the starry sky. It is one of the first natural phenomena that was investigated by humans. An ob-server starts by learning the constellations in the sky and their relative position by stargazing with the ”naked eye”. More advanced amateur astronomers make use ofbinocularsandtelescopeswith which many more objects can be observed.
98 Chapter 8: Augmented Astronomical Telescope
Goto (motorized) telescopes are gaining in popularity. Many newcomers pur-chase one as their first telescope. These telescopes find a target object in the sky by following its selection from a hand controller. The user then expects for an ”in-stant success” in the observations. This surely happens when ”easy to observe”, bright objects such as the Moon or the planets are the targets. However, when observing faintdeep sky objects(astronomical objects which lie outside our solar system) like galaxies or nebulae, much of the initial enthusiasm is lost. These appear as fuzzy grey spots in the telescope’s eyepiece and leave the observer quite unimpressed, possibly thinking about giving up his new hobby. The main reason is that the image in the eyepiece is not really similar to the well known images recorded by the Hubble Space Telescope [NASA a] (or some other large aperture Earth-bound telescopes) which are familiar to the newcomer through astronomy websites or magazines.
One possibility to attain interactivity during astronomical observation is to use an electronic eyepiece, a web-camor a custom CCD camera to display the live image formed at the telescope focus on a TV or computer screen. However, this approach only works for bright astronomical objects and needs a skilled observer to fit the image of the desired object on the CCD chip.
We propose a system which augments the view through the eyepiece of an as-tronomical telescope in order to provide additional online information to the user during observation. The system overlays the currently visible object with a long exposure image of it, as a visual aid. The present orientation of the telescope is continuously queried and the currently visible sky section is computed in real time by a portable computer. It is also possible to overlay animations for specific ob-jects. The system is not meant to replace traditional deep sky observation. Rather, it is intended more aseducationalandvisual aid for the novice astronomer.
The main motivation of our work is to increase the interest in astronomy among the general public who are quite unimpressed after their first glimpse through a telescope. As the human eye has a limited capacity to integrate capture light over time, faint deep sky objects are perceived vaguely, and the observer cannot de-termine their structure. Our system gives observers the ability to simultaneously compare the visually perceived object with a photograph acquired using long ex-posure. When observing the planets it is often difficult to identify their natural satellites because of their fast movement relative to the position of the planet due to short orbital periods. Our system can help the stargazer by overlaying the names of the visible natural satellites. The same approach is used when observing dim stars which can also be hard to identify in a field containing a considerable number of stars.
In the following section we present an overview of the related work in the field