Exercises
- Give a definition of an implicit surface and give three examples of
where such things might be useful.
- Explain how voxel data can be thought of a defining an implicit
surface (or surfaces). Explain, conversely, an implicit surface can be
converted into voxel data.
- Following Section 4 of Lorenson and Cline's paper, sketch an
implementation of the two-dimensional `marching squares' algorithm --
where you generate line segments in 2D rather than triangles in 3D. An
appliation of this algorithm would be the drawing of isobars on a
weather map, given pressure values at a regular (2D) grid of
points. [This question is practically identical to the exam question
below.]
- [2001/7/9] (a) The marching squares algorithm is a
two-dimensional version of marching cubes, where you generate line
segments in 2D rather than triangles in 3D. It could be used, for
example, where you have a regular grid of height values and want to
draw contours of constant height. Sketch an implementation of this
two-dimensional marching squares algorithm. [6 marks]
- Medical data is captured in slices. Each slice is a 2D image of
density data. The distance between slices may be different to the
distance between the pixels within a slice (for example, see Lorenson
and Cline, Section 7.1, p. 167). What effect, if any, does this
difference have on the voxel data? What effect, if any, does it have
on the marching cubes algorithm?
- Consider Lorenson and Cline, Section 6. This research was done
about fifteen years ago. Given your knowledge of processor performance,
what differences in performance would you expect to see between then
and now?
- Lorenson and Cline is an example of a graphics research
paper. Critically evaluate Lorenson and Cline. How good is this piece
of research?
- Research papers at the SIGGRAPH conference are limited in their
length. Evaluate Lorenson and Cline in terms of the following
questions. What has been left out that would have been useful? What
has been included that could have been left out? Where could the
explanation have been better? Are any of the figures extraneous? Where
would an extra figure have been helpful? For light relief, list any
grammatical or spelling errors that you find (there is at least one of
each).
- [2002/8/4] (b) Implicit surfaces are normally combined by adding the field
functions together to create a "blobby" blended surface. Describe an
alternative mechanism (or mechanisms) for combining implicit surfaces
which would produce results more akin to CSG union and
intersection. Explain why it produces these results. Given this
mechanism, suggest a way of combining implicit surfaces to produce a
result similar to CSG dierence. [4 marks]
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Advanced Graphics Study Guide