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Forest biomass estimation with hemispherical photography for multiple forest types and various atmospheric conditions
The importance of accurately identifying inventories of domestic energy, including forest biomass, has increasingly become a priority of the US government and its citizens as the cost of fossil fuels has risen. It is useful to identify which of these resources can be processed and transported at the lowest cost for both private and public landowners. Accurate spatial inventories of forest biomass can help landowners allocate resources to maximize forest biomass utilization and provide information regarding current forest health (e.g., forest fire potential, insect susceptibility, wildlife habitat range). This research has indicated that hemispherical photography (HP) may be an accurate and low cost sensing technique for forest biomass measurements.
In this dissertation:
It is shown that HP gap fraction measurements and both above ground biomass and crown biomass have a linear relationship.
It is demonstrated that careful manipulation of images improves gap fraction estimates, even under unfavorable atmospheric conditions.
It is shown that estimates of Leaf Area Index (LAI), based on transformations of gap fraction measurements, are the best estimator for both above ground forest biomass and crown biomass.
It is shown that many factors negatively influence the utility of HP for biomass estimation.
It is shown that biomass of forests stands with regular spacing is not modeled well using HP.
As researchers continue to explore different methods for forest biomass estimation, HP is likely to remain as a viable technique, especially if LAI can be accurately estimated. However, other methods should be compared with HP, particularly for stands where LAI is poorly estimated by HP
Hardware-supported cloth rendering
Many computer graphics applications involve rendering humans and their natural surroundings, which inevitably requires displaying textiles. To accurately resemble the appearance of e.g. clothing or furniture, reflection models are needed which are capable of modeling the highly complex reflection effects exhibited by textiles. This thesis focuses on generating realistic high quality images of textiles by developing suitable reflection models and introducing algorithms for illumination computation of cloth surfaces. As efficiency is essential for illumination computation, we additionally place great importance on exploiting graphics hardware to achieve high frame rates. To this end, we present a variety of hardware-accelerated methods to compute the illumination in textile micro geometry. We begin by showing how indirect illumination and shadows can be efficiently accounted for in heightfields, parametric surfaces, and triangle meshes. Using these methods, we can considerably speed up the computation of data structures like tabular bidirectional reflectance distribution functions (BRDFs) and bidirectional texture functions (BTFs), and also efficiently illuminate heightfield geometry and bump maps. Furthermore, we develop two shading models, which account for all important reflection properties exhibited by textiles. While the first model is suited for rendering textiles with general micro geometry, the second, based on volumetric textures, is specially tailored for rendering knitwear. To apply the second model e.g. to the triangle mesh of a garment, we finally introduce a new rendering algorithm for displaying semi-transparent volumetric textures at high interactive rates.Eine Vielzahl von Anwendungen in der Computergraphik schließen auch die
Darstellung von Menschen und deren natürlicher Umgebung ein, was zwangsläufig auch die Darstellung von Textilien erfordert. Um beispielsweise das Aussehen von Bekleidung oder Möbeln genau zu erfassen, werden Reflexionsmodelle benötigt, die in der Lage sind, die hochkomplexen Reflexionseffekte von Textilien zu berücksichtigen. Der Schwerpunkt dieser Dissertation liegt in
der Generierung qualitativ hochwertiger Bilder von Textilien, was wir durch
die Entwicklung geeigneter Reflexionsmodelle und von Algorithmen zur Beleuchtungsberechnung an Stoffoberflächen ermöglichen. Da Effizienz essentiell
für die Beleuchtungsberechnung ist, nutzen wir die Möglichkeiten von
Graphikhardware aus, um hohe Bildwiederholraten zu erzielen. Hierfür legen wir eine Vielzahl von hardware-beschleunigten Methoden zur Beleuchtungsberechnung der Mikrogeometrie von Textilien vor. Zuerst zeigen wir, wie indirekte Beleuchtung und Schatten effizient in Höhenfeldern, parametrischen Flächen und Dreiecksnetzen berücksichtigt werden können. Mit Hilfe dieser Methoden kann die Berechnung von Datenstrukturen wie tabellarischer bidirectional reflectance distribution functions (BRDFs) und bidirectional texture functions (BTFs) erheblich beschleunigt, sowie die Beleuchtung von Höhenfeld-Geometrie und Bumpmaps effizient errechnet werden.Weiterhin entwickeln wir zwei Reflexionsmodelle, welche alle wichtigen Reflexionseigenschaften berücksichtigen, die Textilien aufweisen. Während das erste Modell sich zur Darstellung von Textilien mit allgemeiner Mikrogeometrie eignet, ist das zweite, welches auf volumetrischen Texturen basiert, speziell auf die Darstellung von Strickwaren zugeschnitten. Um das zweite Modell z.B. auf das Dreiecksnetz eines Bekleidungsstückes anzuwenden führen wir einen neuen Renderingalgorithmus für die Darstellung von semi-transparenten volumetrischen Texturen mit hohen Bildwiederholraten ein