Changeset 266 for trunk/VUT/doc/SciReport/sampling.tex

Timestamp:

09/13/05 18:44:54 (19 years ago)

Author:

bittner

Message:

structural changes

File:

• trunk/VUT/doc/SciReport/sampling.tex (modified) (14 diffs)

trunk/VUT/doc/SciReport/sampling.tex

@@ -1 +1 @@
 \chapter{Global Visibility Sampling Tool}
-
-
-\section{Introduction}
 
 
@@ -21 +18 @@
 conservative or error bound aggresive solution. The choice of the
 particular verifier is left on the user in order to select the best
-for a particular scene, application context and time constrains. For
-example, in scenes like a forest an error bound aggresive visibility
-can be the best compromise between the resulting size of the PVS (and
-framerate) and the visual quality. The exact or conservative algorithm
-can however be chosen for urban scenes where of even small objects can
-be more distructing for the user. The mutual visibility tool will be
-described in the next chapter.
+one for a particular scene, application context and time
+constrains. For example, in scenes like a forest an error bound
+aggresive visibility can be the best compromise between the resulting
+size of the PVS (and framerate) and the visual quality. The exact or
+conservative algorithm can however be chosen for urban scenes where
+ommision of even small objects can be more distructing for the
+user. The mutual visibility tool will be described in the next chapter.
 
 \end{itemize}
@@ -35 +32 @@
 subdivided into viewcells and for each view cell the set of visible
 objects --- potentially visible set (PVS) is computed. This framewoirk
-has bee used for conservative, aggresive and exact algorithms.
+has been used for conservative, aggresive and exact algorithms.
 
 We propose a different strategy which has several advantages for
@@ -41 +38 @@
 based on the following fundamental ideas:
 \begin{itemize}
-\item Replace the roles of view cells and objects
 \item Compute progressive global visibility instead of sequential from-region visibility
+\item Replace the roles of view cells and objects for some parts of the computation
 \end{itemize}
 
@@ -52 +49 @@
 \label{VFR3D_RELATED_WORK}
 
-
- Below we briefly discuss the related work on visibility preprocessing
+Below we briefly discuss the related work on visibility preprocessing
 in several application areas. In particular we focus on computing
 from-region which has been a core of most previous visibility
@@ -63 +59 @@
 The first algorithms dealing with from-region visibility belong to the
 area of computer vision. The {\em aspect
-graph}~\cite{Gigus90,Plantinga:1990:RTH, Sojka:1995:AGT} partitions
+  graph}~\cite{Gigus90,Plantinga:1990:RTH, Sojka:1995:AGT} partitions
 the view space into cells that group viewpoints from which the
 projection of the scene is qualitatively equivalent. The aspect graph
@@ -237 +233 @@
 attenuation, reflection and time delays.
 
-\section{Algorithm Setup}
+\section{Algorithm Description}
+
+This section first describes the setup of the global visibility
+sampling algorithm. In particular we describe the view cell
+representation and the novel concept of from-object based
+visibility. The we outline the different visibility sampling
+strategies.
 
 \subsection{View Cell Representation}
@@ -247 +249 @@
 \item optimized for viewcell - ray intersection.
 \item flexible, i.e., it can represent arbitrary geometry.
-\item naturally suited for an hierarchical approach. %(i.e., there is a root view cell containing all others)
+\item naturally suited for a hierarchical approach. %(i.e., there is a root view cell containing all others)
 \end{itemize}
 
@@ -257 +259 @@
 subdivide a BSP leaf view cell quite easily.
 
-Currently we use two approaches to generate the initial BSP view cell tree.
+Currently we use two approaches to generate the initial BSP view cell
+tree.
 
 \begin{itemize}
+
 \item We use a number of dedicated input view cells. As input view
 cell any closed mesh can be applied. The only requirement is that the
@@ -270 +274 @@
 (i.e., add a pointer to the view cell). Hence a number of leafes can
 be associated with the same input view cell.
+
 \item We apply the BSP tree subdivision to the scene geometry. When
 the subdivision terminates, the leaf nodes also represent the view
 cells.
+
 \end{itemize}
 
 \subsection{From-object based visibility}
 
-Our framework is based on the idea of sampling visibility by casting
+ Our framework is based on the idea of sampling visibility by casting
 casting rays through the scene and collecting their contributions. A
 visibility sample is computed by casting a ray from an object towards
@@ -304 +310 @@
 
 
-\section{Basic Randomized Sampling}
+\subsection{Basic Randomized Sampling}
 
 
@@ -319 +325 @@
 
 
-The described algorithm accounts for the irregular distribution of the
+ The described algorithm accounts for the irregular distribution of the
 objects: more samples are placed at locations containing more
 objects. Additionally every object is sampled many times depending on
@@ -327 +333 @@
 
 
-\section{Accounting for View Cell Distribution}
-
-The first modification to the basic algorithm accounts for irregular
-distribution of the viewcells. Such a case in common for example in
+\subsection{Accounting for View Cell Distribution}
+
+ The first modification to the basic algorithm accounts for irregular
+distribution of the viewcells. Such a case is common for example in
 urban scenes where the viewcells are mostly distributed in a
 horizontal direction and more viewcells are placed at denser parts of
 the city. The modification involves replacing the uniformly
 distributed ray direction by directions distributed according to the
-local view cell directional density. It means placing more samples at
-directions where more view cells are located. We select a random
+local view cell directional density. This means placing more samples at
+directions where more view cells are located: We select a random
 viecell which lies at the halfpace given by the surface normal at the
 chosen point. We pick a random point inside the view cell and cast a
@@ -342 +348 @@
 
 
-\section{Accounting for Visibility Events}
+\subsection{Accounting for Visibility Events}
 
  Visibility events correspond to appearance and disapearance of
  objects with respect to a moving view point. In polygonal scenes the
- events defined by event surfaces defined by three distinct scene
- edges. Depending on the edge configuration we distinguish between
- vertex-edge events (VE) and tripple edge (EEE) events. The VE surfaces
- are planar planes whereas the EEE are in general quadratic surfaces.
+events defined by event surfaces defined by three distinct scene
+edges. Depending on the edge configuration we distinguish between
+vertex-edge events (VE) and tripple edge (EEE) events. The VE surfaces
+are planar planes whereas the EEE are in general quadratic surfaces.
 
  To account for these event we explicitly place samples passing by the
- object edges which are directed to edges and/or vertices of other
- objects.
-
-
+object edges which are directed to edges and/or vertices of other
+objects.
+
+